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STRIPED BASS

REARING EXPERIMENTS 1976

FOR

CONSOLIDATED EDISON COMPANY OF NEW YORK, INC. AT

GORHAM, ILLINOIS RESEARCH FACILITY

BY DRS. WILLIAM M. LEWIS AND

ROY C. HEIDINGER, PRINCIPAL INVESTIGATORS BRUCE L. TETZLAFF, RESEARCHER

COOPERATIVE FISHERIES RESEARCH LABORATORY SOUTHERN ILLINOIS UNIVERSITY AT CARBONDALE

May 1977

TABLE OF CONTENTS

PageText

I NT ROD UCT ION METHODS AND PROCEDURES

System Design Rearing Unit Design - Stage I

Stocking -Stage I Feeding -Stage I Harvesting - Stage I

Rearing Unit Design - Stage II

Stocking -Stage II Feeding -Stage II

Harvesting - Stage II Monitoring Stage I and Stage II

RESULTS - STAGE I Water Flow Feeding Cannibalism L.,oss of Fish

RESULTS - STAGE II Water Flow Feeding ;rowth in Length cda 1n ib al1 i sm LOSS of Fish

SW-VI7LUBLADDER INFLATION

BEHiA VI OR WATER QUALITY D TI SC USS I ON

Water Flow Fee ding Growth in Length Swimb ladder Inflation Water Quality

Tabular Data Page

Table 1 Flush rates and water velocities 44

Table 2 Mortality of larval striped bass during shipping

and the first 24 hours after stocking 45

Table 3 Stage II diets used in conjunction with brine

shrimp nauplii 46

Table 4 Survival of striped bass larvae under various

types of rearing conditions 47

Table 5 Survival of striped bass under various water

flow conditions, Stage 1 48

Table 6 Cause of mortality and estimated number of

fish lost 49

Table 7 Survival of striped bass fingerlings in eight circular tanks with various water flow patterns, Stage 11 50

Table 8 Results of the final harvest at completion of Stage 11 51

Table 9 Percent of sampled fish 30 days and older with inflated swimbladders 52

Table 10 Swimbladder inflation statistics during the Stage II water flow rearing conditions 53

Table 11 Swimbladder inflation in relation to the

Stage II diets 54

Table 12 Range of physiochemical parameters 55

Figures Pg

Figure 1A

Figure lB

Figure 2

Figure 3

Figure 4

Figure 5

A simplified flow chart of the various stocking and feeding regimes, Striped Bass Rearing Experiments 1976.,,Stage I

A simplified flow chart of the various stocking and feeding regimes, Striped Bass Rearing Experiments 1976. Stage II

Rate of growth of striped bass in all rearing units based on a total sample of 1,795 fish.

Comparison of the growth rate of striped bass in modified upflow and circular flow during

Stage II.

Proportion of fish less than 30 days old with inflated swimbladders (based on roe number).

Time of swimbladder inflation of striped bass in all rearing units based on a total sample of 2,090 fish.

iii

P age

Appendices

Appendix 1

Appendix 2

Appendix 3

Appendix 4

Appendix 5

Feeding schedule

Mortality of striped bass under various rearing regimes

Daily physical and chemical parameters under the various rearing regimes

Survival index of'striped bass under various rearing regimes

Method of calculating tangential velocity in circular flow tanks

Page

63

67

94

150

197

T E x T

INTRODUCTION

This is a report on the third year of a project designed to

perfect a method of raising striped bass in tanks from one-day-old

larvae to stockable size, 6 to 8 cm fish. These studies were

intended to serve as a basis for the development of an optimal

combination of rearing unit, stocking density, and feeding regime

to maximize survival of striped bass from larvae to advanced

fingerlings. Results from the work done in 1974 and 1975 indi

cated that an upflow type of rearing unit gave 3 to 19 times

better survival than a circular flow, downflow, or raceway unit

for the first five days of life. The results also showed that

striped bass larvae may be favored by a temperature in the order

of 25 C, that cannibalism is a major cause of mortality, and that

the striped bass larvae will not accept Abernathy's Starter until

they are approximately 18 mm lon'g.

The design for the present study included the use of tanks

with an upflow type of water movement for varying periods,

adjustment of water temperature to 25 C, and the use of five diets

(fresh fish eggs, TetraMin, Silver Cup Diet, Abernathy's Diet,

and grindal worms) in conjunction with live brine shrimp nauplii.

A simplified flow chart of the various stocking and feeding

regimes is presented in Figures 1A and lB.

In order to examine various stocking regimes, four upflow

tanks (29-32) were harvested when the larval striped bass were

10 days old. T hese fish were stocked into circular tanks to

begin Stage II experiments, which examined the effects of density

and various diets on advanced larvae. Larvae in eight upflow

tanks (25-28 and 29-32 after being restocked) entered the Stage II

portion of the study when they were harvested at ages greater than

10 days. Two upflow tanks (23 and 24) and three circular flow

tanks (1, 2 and 10) were not harvested. These tanks became a part

of the Stage II feeding studies at 10 days and served as controls

on the change from upflow to circular and other water flow

patterns.

METHODS AND PROCEDURES

System Design

The rearing facility used in the 1976 study was the same as

that used the previous year with certain design and operational

modifications. A schematic diagram of the system can" be found in

Striped Bass Rearing Experiments 1975, Fig. 1 (Lewis and Heidinger

1976). In the 1976 study the 5 redwood tanks, the 10 aluminum

raceways, and the 4 fiberglass tanks designed to receive hot water

were not used. This reduced the total system volume from 104,100

liters (27,500 gallons) to 75,700 liters (20,000 gallons). In

this study the system was operated on 100% recycle, except as

necessary to replenish water lost to seepage, or later in the

season when water was used to control maximum temperature. Thus,

during the first 2 weeks of the s tudy a daily addition of 34,000

liters 1(9,000 gallons) of conditioned well water (45% of the

system volume) was required to accommodate for leakage of the

storage tank until it sealed. From 3 to 12 August, 90% of the

system volume (68,000 liters or 18,000 gallons) was added daily to

lower the temperature. During the majority of the study (9 weeks),

daily makeup was reduced to 8.5% of the system volume (6,400 liters

or 1,700 gallons).

A third modification allowed for the water to be heated. The

original system was designed so that four circular tanks (19-22)

would receive heated water. For the present study, it was neces

sary that all tanks receive heated water; therefore, additional

heaters were installed and slight modifications in the storage

tower were made, enabling heated water to cycle into the main

storage reservoir. The four tanks designed specifically to receive

heated water were not used for this study.

Rearing Unit Design - Stage I

In the present study the newly hatched larvae were stocked

into the ten 670-liter wooden upflow units used in 1975 (tanks

23-32), and two 1,825-liter fiberglass circular flow tanks

(1 and 2) which served as controls for upflow versus circular

flow. The control function of tanks 1 and 2 ended when all larvae

died after three days (Table 5 and Appendix 2). These tanks were

then modified to form a simplified upflow. Water was released at

the bottom from a coiled polyethylene pipe in which thirty-five

3.75 mm holes had been drilled. Inasmuch as 100% mortality

occurred in these tanks (Table 5 and Appendix 2), the upflow

modifications were removed, returning tanks 1 and 2 to circular

flow patterns. Photographs and diagrammatic sketches of the various

rearing units can be found in Lewis and Heidinger (1976) Figure

2-5, 11 and 12.

To examine the effects of light on striped bass larvae, tanks

1 and 2 were next modified by lining their sides with black poly

ethylene plastic. To further examine the effects of light, one

circular flow tank (tank 10) was shaded with black woven sunshade

plastic (3 mm mesh giving 10% light transmission).

Flush rates were measured periodically at the input orifices

of circular tanks and at the waste water outputs of the wooden

upflow tanks. The input water to the circular flow tanks were

released from 31.75 mm diameter pipes located on the perimeters

of the tanks. A diagram of these rearing units can be found in

Lewis and Heidinger (1976) Figure 2. To minimize water currents

the input water was directed vertically upward. When'flush rates

surpassed 19 liters/minute the input water was directed vertically

downward. The flush rates and water velocities used during Stage I

and Stage II are summarized in Table 1. Water velocities in the

upflow units were calculated by dividing the flush rate (in cm3 /sec)

by the surface area of the tank. Calculations of tangential

velocities in the circular flow tanks required the following assump

tions: the continuity for constant density flow is applicable,

and the standard velocity for pipe flow occurs in the rearing tank

(Dr. E.L. Dunning, Technology Department, SIU-C, personal commu

nication). Therefore, by assuming a linear relationship between

flush rate and velocity, an estimated tangential velocity of

0.00939 cm/sec is produced for each liter/mmn of flush (0.014

inch/sec/gal/mmn). See Appendix 5 for calculations.

Stocking - Stage I

On 13 May, 1.2 million striped bass larvae were received by

air freight from Texas Instruments, Inc. The 44-hour-old larvae

were shipped in 12 insulated boxes at 100,000 larvae per box

(Table 2). All subsequent shipments were also shipped at 100,000

larvae per box. The stocking procedure began with removing

the bagged larvae from the shipping boxes and placing the bags

into the tanks to be stocked. After tempering periods ranging

from 30 to 70 minutes (Table 2), the bags were opened and the fish

were gradually released.

In this and all subsequent stockings, the equilibration of

temperature in the shipping bag to that of the rearing unit was the

only tempering utilized. The gradual addition of rearing unit

water to the transport bags was attempted twice in order to temper

the larvae to the change in pH (7.1 in the bag to 8.0 in the

rearing unit water). No differential behavior was observed between

tempered and non-tempered larvae. Also, there was concern that

open bag tempering would result in oxygen depletion; therefore

water tempering was discontinued. During the process of stocking

the striped bass larvae experienced a rapid decline in oxygen

(20 ppm in bags to 9 ppm in the rearing units). The larvae also

experienced a sudden exposure to water with a high alkalinity

(300 ppm), present due to the high alkalinity of the water source.

All shipping cartons were opened in subdued light. Even so, the

fish were exposed to an abrupt change in light intensity.

On 18 May, 500,000 fish (64 hours old) were received to

restock tanks from which fish from the first shipment were lost.

Three tanks (25-27) lost fish through escapement, while the two

control tanks (1 and 2) suffered 100% mortalities from flow abra

sion or some other, yet undefined, cause. Tanks 1 and 2 each

received 100,000 fish after first being modified to upflow types.

The remaining 300,000 fish were used to replace fish lost from

tanks 25, 26 and 27 through gaps which opened in the screens when

aluminum rivets corroded. The bag used to stock tank 25 had

broken during shipment, resulting in a loss of 27% (27,000) of the

fish (Table 2).

On 21 May, 600,000 fish (81 hours old) were received. Two

hundred thousand of these fish were used to restock fish lost in

tanks 1 and 2. Prior to stocking, the upflow modifications were

removed and the tank sides were lined with black polyethylene

plastic. The remaining 400,000 fish received on this date were

used to restock tanks 30-32. Tank 32 received 200,000 fish, while

tanks 30 and 31 each received 100,000 (Table 2).

On 2A' May, 300,000 fish (144 hours old) were received and

stocked into tanks 10, 29 and 31. Following stocking, tank 10

was shaded from direct light with woven sunshade plastic. One

bag received in this shipment was broken, with a resultant loss of

20% (20,000) of the fish (Table 2).,

Feeding - Stage I

All fish were maintained exclusively on brine shrimp nauplii

until 9-15 days old. Brine shrimp were terminated as a diet when

the striped bass were 21-26 days old (Table 3). Brine shrimp eggs

(varying quantities as given below) were incubated in 11.4 liters

of 2.72% salt solution for 72 hours. The brine shrimp were ini

tially incubated at 20 C, but during the second week of the study

the air temperature increased, thus permitting the incubation

temperature to be maintained at 25-27 C.

The quantity of brine shrimp fed to each tank (Appendix 1)

was adjusted by varying the degree to which the nauplii were con

centrated after hatching. The nauplii were concentrated by using

10-liter separatory columns (Lewis and Heidinger 1976, Figure 14).

The incubation solution layered in the columns, allowing unhatched

eggs to rise to the surface while the shells of eggs which had

already hatched sank. The live nauplii initially occupied the

entire column, gradually settling to the bottom over a period of

20 minutes. Thus, by adjusting the amount of time given the

nauplii to settle, various concentrations of nauplii were obtained.

Through this procedure 20-70% of the salt solution was removed.

Brine shrimp were fed at hourly intervals by the use of

Neilson Brine Shrimp Feeders. The initial plan was to supply

100,000 larvae with the nauplii from 80 grams of eggs daily for

the first 3 days of feeding (ages 5-7 days). This level was to

be increased to 100 grams of eggs per 100,000 fish per day for

ages 8-14 days, then 150-175 grams for fish 20 days and older.

Using existing stocks of eggs, it was determined that one gram of

eggs produced 296,000 nauplii. With this hatch, the larvae would

receive 237, 296 and 444-518 nauplii per fish per day respectively.

These rates were based on preliminary estimates, and were to be

adjusted depending upon observation of the larvae. Due to the

unavailability of brine shrimp eggs, the amount of eggs which were

incubated (35-190 grams per tank per day) was below the estimated

optimums for much of the study. An alternative source of shrimp

eggs was not discovered until the majority of food-related mor

tality (cannibalism and possibly starvation) had occurred.

Harvesting - Stage I

The major Stage I harvest occurred on 20 and 21 May, when

upflow tanks 29-32 were harvested. The 9 and 10-day-old fish

were 5-7 mm long and therefore could pass through the 3.175 mm

water input holes in the bottom of the upflow tanks. It was thus

necessary to continue the flush on these tanks during the harvest.

Harvesting was accomplished by netting the fish with nylon aquatic

insect nets (0.480 mm mesh). Netted fish were transferred to 15

liter polyethylene buckets and stocked into circular tanks. The

fish were out of water in the nets for less than three seconds.

No mortality occurred while the fish were in the 15-liter trans

fer buckets. Numbers of fish were estimated by sight while in the

transfer buckets. An earlier (18 May) harvest was accomplished

in a similar manner. In this harvest 4,000-7,000 seven-day-old

fish which had not escaped through the screens were removed from

tank 25 prior to its being restocked. The larvae were stocked

into tank 31.

Later harvests (Table 4) were made at a time when the fish

were large enough (21 mm) to allow lowering of the water levels

in the tanks which were to be harvested. This concentrated the

fish so that they spent only 5-7 minutes in the transfer buckets

instead of the 15-20 minutes required in the 20-21 May harvest.

The aquatic insect nets were again used to handle the fish.

Rearing Unit Design - Stage II

When the larvae were 9-10 days old, four upflow tanks were

harvested and the surviving fish stocked into circular tanks.

Of these fish, 149,000 were stocked into 1.83 m diameter circular

tanks under the following conditions:

Tank 13: circular flow at 20,000 fish per tank Tank 14: circular flow at 15,000 fish per tank Tank 15: circular flow at 30,000 fish per tank Tank 16: circular flow at 10,000 fish per tank Tanks 17 and A: modified downflow at 20,000 fish per tank Tank 18: modified upflow at 15,000 fish per tank Tank B: modified upflow at 19,000 fish per tank

Four tanks (13-16) were designed to produce circular flow (Lewis

and Heidinger 1976, Figure 2) , with input water entering the tanks

from single 31.75 mm pipes located at the tank perimeter. Input

water was directed vertically upward until flush rates exceeded

19 liters per minute. At that time the input water was directed

vertically downward. Tanks 17 and A were modified to produce a

downflow (Lewis and Heidinger 1976, Figure 4). Water was released

at the surface from fifteen 4.75-mm outlets located around the

perimeter of the tank. Discharge water passed through sand

covering the tank bottoms, resulting in the entire tank bottom

receiving the discharge water, thus reducing concentrated water

flow. A diagram of the waste water movement in downflow tanks can

be found in Figure 4, Lewis and Heidinger (1976). The third water

flow type consisted of the modified upflow used in tanks 1 and 2

for a portion of Stage I. Upflow tanks 23 and 24 and circular

tanks 1 and 2 were maintained with their original numbers of fish.

In all flow systems the flush was initially started at 4-5 gallons

per minute (15-19 liters per minute) , and gradually increased to

15-20 gallons per minute (57-76 liters per minute) by the completion

of Stage II (Table-1).

Stocking - Stage II

The initial Stage II stocking occurred on 20-21 May when

158,000 striped bass larvae were stocked into circular tanks. The

majority of these fish (149,000) were stocked into the eight

primary Stage II tanks (13-16, A and B). The remaining 9,000 fish

were stocked into tank 12 (circular flow). In later stockings an

additional 71,000 fish were stocked into circular flow tanks 5-9

at rates of 458 to 21,000 fish per tank (Table 4).

Feeding - Stage II

With the initiation of Stage II, combinations of diets were

used. Food used in combination with live brine shrimp nauplii

included TetraMin, Abernathy's and Silver Cup commercial fish

foods, grindal worms (Enchytrae sp.) and fresh fish eggs (Table 3).

The striped bass larvae were 5-7 mm long when artificial

feeding was initiated. We suspected that the dry foods (TetraMin,

4-8 mm flakes; Abernathy's Starter, 0.4-0.6 mm particle; and

Silver Cup Starter, 0.4-1.5 mm particle) were not acceptable to

the striped bass larvae because of the large particle size. Dry

foods were therefore ground to a fine powder (0.1-0.2 mm) using a

Wiley Mill equipped with a number 20 sieve (1.25 mm mesh).

Grindal worms were cultured on 32 glass plates 28 by 28 cm

placed on damp soil. Rolled oats were used as food for the worms.

To feed grindal worms to the fish, a plate was removed from the

culture bed and swirled in the tank water. This released the

worms adhering to the plate.

Fish eggs were surgically removed from ripe females. Ini

tially the eggs of carp (Cyprinus carpio) and-buffalo (Ictiobus.

spp.) were collected. However, it soon became apparent that the

1-2 mm eggs from these fish were too large to be utilized by the

5-15 mm striped bass larvae. The 0.72 mm diameter eggs taken from

gizzard shad (Dorosoma cepedianum) were later used. The eggs were

separated from the ovarian connective tissue by placing 100-300

grams of ovary material in a Waring Blender for four seconds. The

egg mixture was diluted with 400 ml of 40% Nadl and allowed to

settle in graduated cylinders. After 10-15 minutes the heavier

eggs settled below the fragmented ovarian connective tissue.

The required quantity of fish eggs (Appendix 1) were diluted with

100 ml of holding tank water. The egg mixture was then gradually

poured into the rearing tank.

The five foods discussed above were fed at two-hour intervals.

They were fed in combination with brine shrimp nauplii until the

fish were 21 to 26 days old (Table 3) . At this time, feeding of

brine shrimp was discontinued and the fish were continued on dry

food.

Since a wide variety of diets were utilized it was necessary

to feed the larval fish by hand. Hand feeding also permitted us

to spread the food evenly over the surface of the rearing tanks.

The continued use of TetraMin flake food during Stage II prohib

ited the use of automatic feeders on some tanks. During Stage II

the fish were gradually brought through successively larger sizes

of Abernathy's and Silver Cup food. Ground TetraMin was fed

until supplies were depleted on 14 June. Tanks receiving this

diet were transferred to Silver Cup until 14 July, when unground

small flake Tetraiin became available.

Harvesting - Stage II

Based on size, assumed cannibals were removed from circular

flow tanks 10, 16 and 17 on 27 June. In this and all following

harvests of the circular tanks the water level in the tank to be

harvested was lowered to a depth of 20-25 cm (8-10 inches). The

striped bass were concentrated in one-half of the'tank, using a

wood and fiberglass divider. The fish were netted with a hand

dip net (4.76 mm mesh) and the cannibals were removed. Fish

remaining in the net were then immediately placed in the previously

cleared side of the tank. Assumed cannibals were transferred to

tank 12 or tank 6 depending upon their size. The smaller fish were

removed from the water for 1-2 seconds during this procedure.

Twenty-eight fish died during the removal of cannibals, apparently

because of mechanical damage. Because of the mortality, and to

maintain one tank with obvious differential growth as a control,

no cannibals were removed from circular flow tank 8.

The final harvest occurred on 5, 11 and 12 August. In order

to rapi dly estimate the number of fish in each rearing unit, the

average weight method was utilized. The tanks were lowered to

one-third their normal depth, and a sample of fish (ranging from

52-110) was netted from the tank to be harvested. The fish were

weighed and the mean weight recorded. Dividing this mean weight

into the total weight of fish in the tank gave an estimate of the

total number.

Monitoring Stage I and Stage II

Physiochemical parameters were taken at the outputs of each

of the four biofilter modules, the input to one circular tank,

the mid-depth of all circular tanks containing fi sh, and the

waste water of all upflow tanks containing fish. Water tempera

ture, dissolved oxygen, and pH were determined daily. Ammonia

nitrogen, nitrite-nitrogen, and nitrate-nitrogen concentrations,

and methyl orange alkalinity were determined twice a week. In

addition, the temperature of the hot water storage section of the

aeration-storage tower was monitored.

Dissolved oxygen was measured with a YSI model 54 meter. The

pH and methyl orange alkalinity (M.O.A.) were determined with a

Beckman model 12 pH meter. The nitrogen content of the water was

monitored using a Hach dr-2 water analysis kit.

Daily monitoring of the fish included survival index, a count

of the observable mortality, and a short description of the distri

bution of fish within each tank. The survival index consisted of

random counts of the number of fish appearing over a 3 by 5 inch

(76 by 127 mm) white bakelite sheet suspended over the bottom of

the tank. Three counts were made from each tank; one near the

perimeter, one mid-way between the perimeter and the center, and

one near the center. Once the fish reached 25-30 mm they avoided

the plastic sheet. When this occurred the use of the bakelite

sheet was discontinued. The counts were made in approximated

areas with the same surface area as the plastic sheet (9,652 mm).

Samples of fish were netted from each tank twice a week.

Care was taken to assure that samples were representative of fish

from all portions of the tank. Five fish were chosen from each

sample and microscopically examined to determine the type and

quantity of food in the stomach, the state of development of the

swimbladder, and the total length. Care was again taken to assure

that the subsamples represented all size classes present in the

sample in approximately the same frequency. Samples were fixed

in formalin and stored in alcohol.

The unweighted mean length of 359 fish samples were determined

during Stage II. Tanks 6 and 8 were excluded, since sampling was

discontinued due to the low number of surviving fish. Tests of

significance were made on the 359 unweighted means using the

F-tests of program DPLINEAR. -The growth rates as determined from

all fish samples (2,090 fish) were plotted.

RESULTS

Stage I

Water flow

Larval fish were stocked into two major types of water flow

systems: an upflow system which produced an upward columnar flow

of 0.04 cm/sec at a 5 gpm flush rate, and a circular flow which

produced a flow of 31.9 cm/sec at the orifice (at 5 gpm). Flow

rates in the various rearing units are given in Table 1. Upflow

modifications in circular tanks 1 and 2 did not prevent the

larvae from coming in contact with areas of relatively high

velocity water flow (45.5-68.3 cm/sec at the orifice). One

hundred percent mortality occurred in tanks 1 and 2 in two sepa

rate stockings, both within three days of stocking (Table 5).

With the exception of two tanks (26 and 27) which lost all

fish through escapement, and one tank which lost 92% (tank 25),,

fish su rvived in all upflow tanks (Table 5). Escapement of fish

from tanks 25, 26 and 27 was the result of separations in the

screens. Aluminum rivets used in constructing the screens corroded

rapidly, producing slight separations which were not visually

apparent because of the design of the screens and the elevation of

the upflow tanks. This was discovered only when fish escaped.

The survival in the upflow tanks which were harvested when the fish

were 9-10 days old (tanks 29-32) varied from 32% to 48%. Upflow

tanks which were harvested later (30 to 44-day-old fish) had consid

erably lower survivals, ranging from 0.03% to 37% and averaging

10.24% (Table 5). An examination of the mortality data indicates

that most of the mortality which occurred in these tanks occurred

before the larvae were 15 days old (Appendix 2). The survival

index data were so variable they could not be used to interpret

mortality patterns (Appendix 4).

Flow rates for Stage I were kept to a minimum during the

rearing of the larvae. Flushes on both the upflow and circular

tanks were maintained at 7.5-11.4 liters (2-3 gallons) per minute

until dry food diets were initiated, after which the flushes were

increased to 19.0-26.5 liters (5-7 gallons) per minute (Table 1).

No mortality or damage to fish was apparent after flush rates

were increased to accommodate for the increase in waste generated

by dry food.

Feeding

The quantities of brine shrimp eggs incubated during Stage I

varied from 34.5 to 189.9 g/tank/day. Because of the unavail

ability of brine shrimp eggs, amounts far below our estimated

requirement of 100 g/tank/day were incubated. The first shipment

of fish (13 May stocking) received an adequate quantity (91.4

g/tank/day) for only 3 days. From 19 May through 6 June the

amounts were reduced to 34-69 g/tank/day. The se cond (18 May)

through fourth (24 May) shipments received the nauplii from

34.5 to 63.2 grams of eggs until the fish were 10-12 days old, at

which time they received the nauplii from 51.6 to 68.9 grams of

eggs (Appendix 1).

Twenty-eight percent of the fish were feeding on shrimp

nauplii at 4 1/2 days. Brine shrimp were still being eaten when

the feeding of them was discontinued at the time the fish were

23 days old and 18 mm long.

Grindal worms never appeared in the stomach contents of

sampled fish. Observations showed that the larval fish watched

the worms but did not eat them.

Striped bass larvae were observed taking fish eggs when the

larvae were 9-10 mm long. However, fish eggs did not appear in

the stomach content samples until the fish were '11 mm long and

17 days old. A microscopic examination of the eggs revealed that

when opened with a fine needle they broke into unrecognizable

semifluid masses. Fish eggs found in the stomach content of

sampled fish were recognized by their yellow oil globules. The

use of fish eggs as food was limited by their availability. The

larvae would accept gizzard shad eggs (0.75 mm in diameter) but

reject carp (1-2 mm diameter) and buffalo (1.2-2..0 mm diameter)

eggs.

During the initial trials the larvae did not attempt to

utilize the commercially prepared foods. On the second day of

feeding some fish were seen to attack and then reject the parti

cles. At this time an attempt was made to use food which was

finely ground. Although no fish were seen utilizing the food in

this form, considerably more attacks were made. The finely ground

food was first observed in the stomach contents of 13 mm fish

(21 days old).

Utilization of TetraMin occurred in a similar manner. Attacks

on particles were made by small fish, but the food did not appear

in the stomach samples until the fish were 14 mm long and 21 days

old.

Cannibalism

Cannibalism was first observed when 11 mm fish were attempting

to prey upon 10 mm fish. Cannibalism occurred with a much higher

frequency among the fish stocked 18-24 'May than among the fish

stocked 13 May. During one period it was estimated that 20% of

the fish in tanks 1 and 2 were cannibals. Although impossible to

accurately determine, it is estimated that 560,000 fish were lost

during Stage I to cannibalism (Table 6 and Appendix 2).

In a sub-experiment independently carried out at the research

facility, a 24-liter (6.4 gallon) clear plastic upwell system was

stocked with 250 twelve-day-old fish (9-10 mm long). Cannibalism

was continuously occurring in this tank, with 6-12 cannibals

observed at all times. Twenty minutes after one liter of

concentrated brine shrimp nauplii was added to the system the

number of observed cannibals was reduced to one. Ten minutes later

no fish were cannibalizing.

Loss of Fish

Mortali ty during Stage I can be attributed to numerous causes

(Table 6). As discussed above, water flow and cannibalism resulted

in losses of 480,000 and 56,000 fish. Fish lost during shipment

and those which died within 24 hours of stocking account for a

loss of 202,000 fish.

A considerable proportion of the losses in the upflow tanks

occurred as a result of fish escaping through damaged screens.

In two upflow tanks (26 and 27), 100% (191,000) of the fish had

escaped within four days of stocking. Tank 25 experienced a 92%

escapement (88,000 fish) during the same period. Throughout

Stage I, escapement resulted in losses of 20,000, 9,000, 5,000,

75,000, and 20,000 fish from tanks 26, 28, 30, 31 and 32 (Table 6

and Appendix 2). Survival during Stage I, not including the fish

lost during stocking for Stage II, was approximately 12%.

Stage II

Water Flow

Of the 158,000 fish stocked into Phase II systems on 20-21

May, 73% (117,000) died within 56 hours of stocking. No

differential mortality among the water flow types was apparent.

Harvesting of these tanks occurred 67-73 days after stocking.

Survival at harvest among the three water flow types varied from

6.1 to 8.1% (Table 7). No accurate pre-Stage II estimates of

survival in the four control tanks could be made.

Feeding

During Stage II, three primary feeding regimes were used:

Silver Cup salmon food, Abernathy's salmon food, and TetraMin

aquarium fish food. These diets were used in combination with

brine shrimp nauplii until the fish were 26 days old (Table 3).

For the majority of the experiment, 3 tanks received Abernathy's,

4 tanks received TetraMin, and 13 tanks received Silver Cup

(Appendix 1). Survival to harvest varied slightly in the eight

major Stage I-I tanks (13-18, A and B); the two tanks (13 and 15)

which were fed Abernathy's averaged 9.0% survival. The four tanks

receiving TetraMin (14, 16, 17 and B) averaged 7.3% survival,

while tanks 18 and A, which received Silver Cup, averaged 6.2%.

On 14 June, tank 12 was switched from a Silver Cup to Abernathy's

diet. This tank had a 12.5% survival.

Growth in Length

The striped bass exhibited a sigmoid growth curve during the

1976 rearing experiments (Figure 2). The equation:

L= 12.2911 - 0.8588(A) + 0.0450(A2 ) - 0.0003 (A3 )

(where L= total length in mm and A= age in days). R2 , the coef

ficient of condition (Kerlinger and Pedhazer 1973, p. 36-39),

equalled 0.9664, thus showing the small degree of variation at

any given age. Figure 2 shows that the greatest growth occurred

between the ages of 20 and 70 days.

Growth of fish 20 days and older was related to roe number

(and thus time of initial stocking). Roe 7 fish (tanks 1, 2, and

10) grew significantly faster than fish from the other roes

(p

The last cannibal to occur in the fish samples was found on

19 June. However, in tank 8, the one Stage II tank which exhibited

differential growth and was not thinned, cannibalism appeared to

continue. Attrition occurred throughout Stage II with a resultant

loss of 7,400 fish. When harvested, 178 fish were present in tank

8 (Table 8).

Loss of Fish

The greatest loss of fish occurring during Stage II was attrib

uted to stocking mortality. Losses resulting from the stocking of

tanks 12-18, A and B totaled approximately 115,000 fish. An esti

mated 50,000 fish were lost in the later stockings of tanks 5-9.

A period of mortality (6,500 fish) occurred when the fish were

approximately 20 days old (Table 6 and Appendix 2). Another period

of mortality occurred in 30 to 40-day-old fish. During this second

period, observed mortality in the eight major Stage II tanks

totaled 1,868 fish. The two tanks on the Abernathy's diet lost

an average of 56.5 fish per tank. The four tanks being fed

TetraMin lost an average of 307.2 fish per tank, while the two

tanks on a Silver Cup diet lost an average of 263.0 fish per tank.

Tank 12 was switched to an Abernathy's diet at 34 days. Of the

100 fish lost during this mortality period, 72 died before the

change in diet.

Water quality contributed to mortality in several tanks during

Stage II. Approximately 3,400 fish were lost, primarily due to

oxygen depletions in tanks 12, 23 and 24 (Appendix 2).

Total survival at the end of Stage II was 2.182%. This figure

includes the larval mortalities which occurred in tanks 1, 2, 10,

23 and 24. A total of 20,172 fish weighing 205.5 kg were harvested

(Table 8). Total survival based on all fish stocked from 13 May

was 0.772%. Survival during Stage II was 6.8%. Stage II stocking

mortality accounts for approximately 73% of the mortality (Table 6).

SWIMBLADDER INFLATION

Swimbladder inflation became evident when the striped bass

larvae were 6 to 8 days old. At 9 days of age 51% of the larvae

sampled had inflated swimbladders (Figure 4) . The proportion of

fish with inflated swimbladders increased until the larvae were

20 to 25 days old (Figures 4 and 5). Samples of fish aged 7-30

days demonstrated that Roe I fish had an average of 67% inflated

swimbladders. Roe 4 and Roe 7 fish averaged 87% and 74% inflated

swimbladders over this same period. Due to the high variability

in the samples (Figure 4) , and the inability to obtain accurate

mortality rates during this period, no analysis can be made of

roe batch correlations. Within the feeding and temperature

regimes of this study, no change in the proportion of fish with

inflated swimbladders was apparent after the larvae were 30 days

old (Figure 5). The estimated proportion of fish with inflated

swimbladders can be predicted with the equation:

P= 0.240 + 0.372 log(A)

where P is the proportion of fish with inflated swimbladders and

A equals age in days. The R2 of this equation was 0.1606. The

instantaneous rate of change in the number of fish with inflated

swimbladders was less than one percent per day when the fish were

37.5 days old. When the fish were harvested at 86 and 94 days,

91.16% had inflated swimbladders.

Swimbladder inflation statistics determined from samples of

fish 30 days and older ranged from 53.85% to 100% (Table 9).

Roe 1 fish had 89.88% inflated swimbladders, while roe 4 and roe 7

fish had 95.23% and 91.22% inflated swimbladders.

In the eight major Stage II tanks (13-18, A and B) the per

centage of fish with inflated swimbladders varied from 81.11% to

100%. The Stage II circular flow tanks averaged 88.30% inflation,

the modified upflow tanks averaged 92.04%, and the modified down

flow tanks averaged 95% (Table 10). Table 10 also sh-ows that

samples of striped bass from the circular tanks used as controls

aver aged 88.02% in flated swimbladders, while samples from the two

control upflow tanks averaged 63.30%. Tanks receiving the

Abernathy's Diet during Stage 11 (13 and 15) averaged 84.67%

swimbladder inflation. Fish fed Silver Cup (18 and A) or TetraMin

(14, 16, 17 and B) averaged 94.64% and 94.82% inflated swimbladders

(Table 11).

Oxygen depletions resulted in mortalities in tanks 12, 23

and 24. Following these mortalities an examination of both

living and dead fish was made. Samples of 15 surviving fish were

taken from tanks 23 and 24. All had inflated swimbladders.

Because of rapid decomposition of the fish, swimbladder inflation

was difficult to determine in the fish which had died in these

tanks. For this reason swimbladder inflation could not be deter

mined in any of the dead fish in tank 23 and 21% of the fish which

had died in tank 24. Fish which died as a result of the oxygen

depletion in tank 12 on 28 July were preserved more rapidly. A

sample of 25 fish was taken from the 280 fish which died. None

of these fish had inflated swimbladders. An estimated 78.57% of

the fish in this tank had inflated swimbladders prior to the mort

ality (55 of 70 fish examined 12 June through 26 July). All fish

examined after the mortality had inflated swimbladders (20 fish

in 4 samples). The mortality resulted in a loss of 19.87% of the

existing fish.

Late swimbladder inflation was not apparent in the circular

flow tanks stocked with 30-day-old fish. In upflow tanks 25-27,

which were harvested at 30 days, the estimated swimbladder infla

tion was 98.94%. Circular flow tanks 5, 7 and 9 were stocked with

fish from these upflow tanks. An estimated 95.23% of these fish

had inflated swimbladders at harvest.

BEHAVIOR

Certain behavioral patterns were displayed by the striped

bass during these experiments. The first of these corresponds to

the time immediately following the stocking of the larvae and at

approximately 12 days thereafter. Despite high oxygen concen

trations in the holding water the larvae exhibited a "piping"i

reaction. Larvae swam at the surface, breaking the surface film,

for 3-5 hours.

A second behavioral characteristic concerns distribution of

larvae in the upflow and circular tanks. In all cases the larvae

were more evenly distributed within the upflow tanks. Fish stocked

into circular tanks were concentrated along the sides. On several

occasions the larvae congregated on the side of the tank exposed

to the maximum amount of light.

During the "30-40 day" mortality experienced in Stage II

the moribund fish demonstrated certain behavioral symptoms. The

fish either became light in color and gasped at the surface, or

made short, darting movements while spinning about their longi

tudinal axis. In both cases this behavior was followed by an

uncontrolled drift toward the bottom. During this downward drift

the moribund fish were frequently attacked by other fish.

Non-cannibalistic attacks were occasionally observed in fish

3-4 cm long. One fish would attempt to bite another along its

side, posterior to the operculum. The attacked fish would then

either flee or retaliate. No mortality could be directly attri

buted to this fighting. However, five fish taken in the

samples had damaged eyes. Whether this was the result of attack

or another factor could not be determined.

The loss of 643,000 fish (25% of the total) is attributed to

cannibalism. The majority of these losses occurred in the younger

fish which were insufficiently fed.

WATER QUALITY

Water quality parameters are summarized in Table 12 and the

raw data are given in Appendix 4. On 13 May tank water temper

atures averaged 17.5 C. This was gradually increased to 25 C by

31 May. From 1 June through 21 July, water temperatures were

maintained between 23 and 26 C. For a period of six days (22

July - 28 July), late afternoon temperatures reached levels ranging

from 27-29 C. Temperatures of 23-26 C were again maintained until

3 August. After this date the water heaters were readjusted and

the well water input was increased. This lowered temperatures to

20-23 C.

The pH ranged from 7.25 to 8.57 during the study. The higher

pH readings occurred in July, when water temperatures had also

increased. Methyl orange alkalinity ranged from 218 to 322 ppm.

The high M.O.A. in the system was related to the fact that the

well water used for filling and maintaining the system had a

methyl orange alkalinity of 377 ppm. No sudden changes occurred

in pH or alkalinity readings.

Ammonia-nitrogen levels were high during the beginning of

the study. Tank ammonia-nitrogen levels ranged from 0.50 to 0.80

mg/liter (0.61 to 0.98 mg/liter total ammonia). During the

remainder of Stage I these decreased to levels ranging from 0.12

to 0.30 mg/liter (0.14 to 0.46 mg/liter total ammonia). Ammonia

levels again increased during the early part of Stage 11 (22 May

21 June) when ammonia-nitrogen ranged from 0.19 to 1.20 mg/liter

(0.23 to 1.46 mg/liter total ammonia). On 22 June the ammonia

levels showed a sudden increase. Tank ammonia-nitrogen averaged

2.08 mg/liter (2.54 mg/liter total ammonia). No mortality occurred

during this period. Similar peaks occurred on 9 and 19 July, and

2 August, resulting in average tank levels of 1.69, 1.20, and 1.39

mg/liter NH 3 -N. Again this resulted in no mortalities.,

The levels of nitrite-nitrogen closely paralleled the ammonia

nitrogen levels. Readings of 0.21, 0.24, 0.20 and 0.15 mg/liter

(0.69, 0.79, 0.66 and 0.50 mg/liter nitrite) were reached on the

days which exhibited high levels of ammonia-nitrogen. Readings

ranging from 0.005 to 0.100 mg/liter (0.01 to 0.33 mg/liter nitrite)

were present during most of the study.

Nitrate-nitrogen levels averaged 1.14 mg/liter (5.02 mg/liter

nitrate) at the beginning of the experiment. They gradually

increased, reaching a maximum average of 6.43 mg/liter (28.29

mg/liter nitrate) on 16 July.

Oxygen concentrations showed wide variations over the term

of this study. During the first week of Stage I they remained

at or above saturation. As water temperatures were increased

dissolved oxygen levels decreased. Recorded oxygen concentrations

during Stage II ranged from 1.6 to 9.0 ppm. The reading of 1.6 ppm

occurred in tank 13 on 18 June. No mortality occurred on this

date; however, most of the fish were gasping at the surface. On

27 July, 30 dead fish were found in tank 15. An oxygen reading

of 2.9 ppm was obtained following this mortality. On 6 July the

flush was terminated on upflow tank 24 in order to repair a damaged

screen. An oxygen depletion resulted, causing a loss of 1,302

fish (90.29%) in this tank. On 26 July a power failure resulted in

the termination of flush to all tanks for 15-20 minutes. This

resulted in a loss of 1,637 fish (91.68%) in upflow tank 23 and

280 fish (19.87%) in circular flow tank 12.

DISCUSSION

Water Flow

This study confirms the conclusion of our 1975 investigations

that an upflow type of water movement, as compared to circular

flow, favors survival of striped bass larvae for the first 10 days

after hatching. The reasons for the mortality in the circular

flow tanks remain unclear. High energy expenditures in unfavorable

water flows may be the cause. However, in 1975, stocking larvae

into darkened tanks resulted in an average survival of 28.75% for

the first five days, compared to 0.08% for undarkened circular

tanks (Lewis and Heidinger 1976). In 1975, some larvae survived

in downflow and "old" circular flow tanks. The downflow tanks had

darkened sand bottoms. A coat of dried organic matter blackened

the sides of the old circular flow tanks. In the present study,

larvae survived in tanks 1 and 2, which were lined with

black polyethylene plastic. Tank 10, which also had some larvae

survive, was shaded with woven sunshade plastic until the fish

were 25 days old. Striped bass larvae stocked into undarkened

circular tanks did not survive for longer than three days (Table 5).

The design of the upflow tanks was such that little direct light

could reach them. Since the larvae which survived in circular

tanks were older than those which died (81 and 142-hour-old larvae

survived, 44 and 64-hour-old larvae did not), no conclusions can

be made. The period of time in the upflows which may be necessary

for survival may be less than 80 hours. However, until the cause

of mortality in the circular tanks can be determined, the upflow

tanks should be used.

The Stage I stocking regime which resulted in the highest

survival involved the harvesting of fish in the upflow tanks and

restocking them into circular tanks at 10 days of age. The pro

cedure resulted in a survival of 3.012%. This figure can be

increased slightly by disregarding the 7,600 fish sacrificed

through sampling and the 15,000 fish lost in shipment. Survival

would be greatly increased if a more effective harvesting and

transfer method could be developed; mortality resulted from the

attempt to transfer fish during the critical period of meta

morphosis. The harvesting of upflow tanks when the fish are older

than 10 days resulted in an average survival of 0.482%. The major

cause of the low survival in this stocking regime is diet related

and will be discussed later. Maintaining fish in upflow tanks

without an intermediate stocking resulted in a survival of 0.144%.

The upflow tanks were designed to maintain larval fish. This

necessitated the use of many small outlets for the dispersement of

flush water. With the current design these small outlets cannot

supply enough water to maintain fingerling fish. Also, screens

fine enough to prevent escapement of larval striped bass are too

fine to allow adequate flushing of the tanks when a dry food diet

is utilized.

Of the three Stage II water flow patterns the circular water

flow resulted in the highest survival. However, the similarities

in the survival rates of these water flow types suggest that the

major cause of mortality in these tanks was not related to this

variable. Stocking density was not significantly correlated to

percent survival in the Stage II tanks (Fisher test for rho - 0,

Minium 1970, p. 319). Stocking densities of 20,000 fish per tank

produced both the highest and lowest survival (10.2% in tank 13,

3.8% in tank 17). Densities of 10,000 and 30,000 fish per tank

resulted in intermediate survivals (Table 8).

Feeding

At this time brine shrimp are an essential component of the

diet of striped bass until the larvae reach 18 mm in length. The

shortage of brine shrimp encountered in this study was the single

most significant cause of mortality in the upflow systems.

Initially, each fish was receiving 241 live nauplii per day.

During the shortage this quantity was reduced to 105 nauplii per

day in the upflow tanks. Fish which were stocked at 9-10 days of

age into Stage II circular tanks were receiving 511 live brine

shrimp per fish. This difference in food availability may explain

the lower rate of cannibalism which occurred in the first shipment

of fish (13 May stocking) . The estimated loss of fish through

cannibalism was 12%. In the later stockings cannibalism resulted

in a 42% mortality. Another factor which contributed to the lower

rate of cannibalism in the Stage II circular tanks is density.

Once these fish were harvested from the upflow tanks and stocked

into circular tanks at 20,000 fish per tank, density was reduced

from 176.53 fish/liter (676 fish/gallon) to 10.99 fish/liter

(42 fish/gallon). However, observations suggest that cannibalism

was lower in tanks 23 and 24. These two tanks, which were stocked

from the first shipment of larvae, remained at the higher density

throughout the experiment.

Growth of fish 20 days and older was related to roe number

and water flow patterns. However, an examination of growth plotted

from the fish sampled during Stage I demonstrates that there is

little variation in growth between the various rearing units or

among roes for the first 20 days. This suggests that there may

be a minimum growth rate which must be maintained. The roe 1 and

4 fish (13 and 18 May stockings) maintained this rate using live

brine shrimp nauplii, while the roe 7 fish (21 and 24 May stockings)

augmented their diet by cannibalism.

In the examination of Stage II feeding regimes, two things

are evident: the modified upflow systems resulted in better

growth during the first few weeks, and Abernathy's Diet resulted

in better survival.

We suspect that the faster growth which occurred in the modi

fied upflow systems is related to food presentation rather than

water flow. In these systems the incoming water did not break

the surface tension; therefore, the finely ground foods floated

for longer periods. In the circular flow and downflow systems

the input water caused the food to sink within five minutes.

It is difficult to compare the other second second stage

foods. Due to the unavailability of proper sized fish eggs, in

sufficient quantities were fed. Fish eggs were heavily utilized

by the striped bass. However, since the fish were not fed quantities

comparable with the dry food diets, growth and survival analyses

would mean little. Grindal worms are apparently too large to be

eaten by larval striped bass.

Particle size is critical for the acceptance of food by larval

striped bass. Although Abernathy's Starter (approximately 0.4 mm

in diameter) can be taken by striped bass less than 16 mm, it is

usually rejected. Finely ground Abernathy's Starter was accepted

by 13 mm fish. Silver Cup salmon starter and TetraMin ground to

a flour consistency was accepted by 13 mm and 14 mm fish respec

tively. Silver Cup salmon starter is not comparable to Abernathy's

starter. Abernathy's consisted of uniform particles with 52%

protein. Silver Cup starter contained an irregular mixture of

large and small particles with 48% protein. Since the initial

food must be ground, Silver Cup No. 1 fry diet may be more accept

able. This diet has a protein content comparable to Abernathy's

Starter. Stage II survival statistics suggest that Abernathy's

Diet results in slightly higher survival. The three tanks receiv

ing this diet (12, 13 and 15) averaged 9.34% survival. The two

tanks utilizing Silver Cup (18 and A) averaged 8.79%, while tanks

14, 16, 17 and B, which received TetraMin, had an average survival

of 5. 43%.

Growth in Length

A major objective of this study was to develop environmental

conditions suitable for rearing striped bass from one-day-old

larvae to a length of 6-8 cm. By maintaining water temperatures

at 25 C, growth was rapid. Lengths of 6-8 cm were achieved when

the fish were approximately 55 days old (Figure 2). Little increase

in length occurred for the first twelve days after hatching. Sub

sequently there wa~s a period of rapid growth which lasted until

the fish were 80 days old.

Baker (1975) reported a linear growth rate in striped bass

reared at Edenton National Fish Hatchery. However, since samples

were made on a monthly basis at Edenton (versus twice per week

for the present study), slight deviations from a linear relation

ship would not have been visible in the Edenton data. Overall

growth in the present study compares favorably with that observed,

at Edenton. Texas Instruments (1976) found an exponential growth

rate in striped bass aged 17-80 days. Although growth rates were

much higher in the present study (with water temperatures 3-5 C

higher than those used by TI), we observed a similar exponential

trend for fish less than 80 days old.

We observed a decrease in growth rate in fish older than 80

days (Figure 2). Texas Instruments (1976) found fish with mean

weights lower than estimated optimums in tanks which had experi

enced high rates of cannibalism. They suggested that the cannibals

had depleted the supply of smaller fish, and that this resulted

in the reduced weight. Cannibalism was not apparent in the present

study after the fish were 40 days old. We postulate that the

decline in growth rate which we observed was the result of dete

riorating water quality which occurred near the end of the study,

or to a change in the body form of the fish. Further, during the

last two weeks of the study there was a decrease in water tempera

ture. While this improved water quality, it also could have

reduced growth. Bonn et al. (1975, p. 83) state that low oxygen

levels reduce food consumption and decrease growth rates in

striped bass. It is also possible that there occurred a change

in the length/weight relationship of the fish that would have

resulted in a decrease in growth in length, but this question is

further complicated by the fact that water temperature and feeding

rate were decreased during the last two weeks of the study.

Swimbladder Inflation

The results of this study suggest that striped bass larvae

inflate their swimbladders between the ages of 4 and 25 days. In

the 1975 study, the striped bass fingerlings were maintained in

upflow rearing units until they were 24 to 43 mm long and 64 days

old. In that study swimbladder inflation percentages were low

in the upflow units, averaging 35.85% (unweighted mean of 235 fish

aged 31 to 64 days). In the present study, sufficient data are

available for three upflow tanks (25-27). At 30 days, when the

fish were harvested, swimbladder inflation average 98.84% (estimated

from a weighted mean of 60 fish). Therefore, the 1975 conclusion

that striped bass can initiate swimbladder inflation as late as

64 days can neither be supported nor refuted by this study.

The reasons for the higher percentage of swimbladder inflation

observed in the 1976 study are unclear. Genetic differences in

brood stock may be one cause. Baker (1975) found that a high

incidence of curved spines and abnormal swimbladders correlated

to a particular roe batch. Other factors which may affect swim

bladder inflation include the higher rearing temperature in 1976

(and thus accelerated development) and the lower initial water

flows used in the upflow tanks (19 liters/mmn. in 1975 and 7.6

to 11.4 liters/mmn. in 1976). Bulak (1976) concluded that the

failure of striped bass to inflate swimbladders was related to

environmental factors. Striped bass reared in ponds had a high

proportion of inflated swimbladders, whereas fish from the same

roe reared in tanks had a much lower proportion. Baker (1975)

found that inflation of the swimbladder was related to the state

of development of the fish. Thus the faster growing fish of this

study may have inflated their swimbladders earlier than those in

the 1975 study. Schwartz (1971) concluded that the failure of

haddock to inflate their swimbladders was due to unfavorable food

and temperature. Lack of proper food would result in slower devel

opment. Low temperature would result both in a slower rate of

development and a lower rate of metabolism. Berg and Stein (1968)

found that a reduction of blood flow through the gas gland signifi

cantly reduced the deposition of gases into the swimbladder. The

lower rate of flush used in the present study reduced the amount

of support created by the upflowing water, and may have stimulated

increased activity in the fish. This in turn would increase metabo

lism as the fish expended energy to remain in the water column.

Fish lacking swimbladders are more vulnerable to oxygen de

pletions than fish with inflated swimbladders. A short term oxygen

depletion in tank 12 appeared to have selectively eliminated the

majority of fish with uninflated swimbladders.

Upflow tanks 23 and 24 produced fewer fish with inflated swim

bladders than the circular tanks holding fish of the same roe.

However, since survival was low no definite conclusions can be

made. The factors which resulted in mortalities in the circular

flow tanks may not be the same as those which resulted in mor

talities in the upflow tanks.

In the eight major Stage II tanks (13-18, A and B) swimbladder

inflation seems to be most closely related to the Abernathy's Diet,

assuming that fish which lack inflated swimbladders have an

energetic disadvantage. The two tanks utilizing this diet (13 and

15) averaged 10% fewer fish with inflated swimbladders. These

tanks also averaged over 2% better survival during Stage II. Lewis

and Heidinger (1976) have discounted the postulate that differential

mortality is the cause of a higher proportion of fish with inflated

swimbladders in circular flow tanks stocked from upflows. Their

observations were based on fish reared in upflow tanks for the

first 64 days, then transferred to circular flow tanks.

Water Quality

Striped bass thrive at a temperature of 25 C. Temperatures

as high as 29 C did not result in mortality of juvenile fish 60-90

mm long and 64-76 days old. At these temperatures growth rates

as high as 1.67 mm/day were achieved. This could result in the

production of stockable sized fish (6-8 cm) in two months. These

fish would have an improved chance for survival after stocking

since their larger size would make them less vulnerable to preda

tion.

The poor water quality which was intermittently experienced

during this study was expected because of two conditions. First,

the large quantities of fine food used resulted in an accumulation

of suspended organic matter. This would account for the rapid

decrease in oxygen concentrations which occurred in the rearing

tanks. A modification which would allow this biofiltered water to

be mechanically filtered is possible with the existing system.

Filtering the recycled water through the pressure filters would

remove particulate organic matter and reduce the oxygen demand in

the system.

The second condition which contributed to poor water quality

was biofilter inefficiency. This resulted in ammonia-nitrogen

levels exceeding 2 mg/liter (2.6 mg/liter total ammonia) and

nitrite-nitrogen levels of 0.24 mg/liter (0.79 mg/liter NO2 ).

Examination of the biofilters at the termination of the study

revealed that the present backwash procedures were inefficient.

Considering the surface area of the biofilter media and the nitro

genous waste production rate of salmon (Meade 1974, p. 15), it was

calculated that the system should accommodate 3,174 kg (7,000 lbs).

During this study difficulty was encountered with a loading rate

of only 205 kg (453 lbs). A modification that would allow a more

complete cleaning of the biofilters would help reduce this problem.

Bonn et al. (1976) state that, with the exception of tempera

ture, water quality criteria used for salmonids are also desirable

for striped bass in order to avoid physiological stress. However,

since the biofilter in the present system did not operate at maxi

mum efficiency because of partial clogging, we now know that the

striped bass has a higher tolerance to nitrogenous pollutants than

do salmonids. In this study striped bass tolerated levels of

ammonia and nitrite which are far greater than those lethal to

salmonids. Although the optimum level of ammonia (< 0.6 ppm)

should be maintained to maximize growth and survival (Bonn et al.

1976) , short-term exposure to higher levels can be tolerated.

The tolerance of striped bass to these high levels of nitro

genous pollutants su ggests that this species is adaptable to

intensive culture. The rearing of fish through intensive culture

has numerous benefits, including ease of harvesting and grading,

and the ability to monitor the fish closely. However, certain

disadvantages exist, particu larly in systems using recirculating

water. Intensive culture operations are more subject to equipment

failure which result in the loss of fish. In a recirculating

system chemicals used as treatments for parasites may suppress or

destroy some of the nitrifying bacteria. When these situations

arise, a heavy flush is necessary to maintain water quality. if

the striped bass were the species being cultured, less concern

about maintaining water quality would be necessary. Methods of

artificial oxygenation could replace much of the water supply

normally needed for these emergencies.

SUMMARY

The three years of research conducted by SIU was undertaken

to identify and attain the environmental conditions required to

maximize the survival of striped bass from one-day-old larvae to

6-8 cm fingerlings. A number of problems related to the survival

of striped bass in a tank rearing system were investigated.

Considerations receiving particular emphasis were: prefeeding

mortality, the inability to feed, cannibalism, and failure of

the fish to inflate their swimbladders.

A number of theories have been developed to explain the c ause

of the prefeeding mortality encountered in circular fiberglass

tanks. Among these are the release of toxins by the fiberglass,

the deleterious effects of light, and unsuitable water flow patterns.

Of the theories proposed, the one concerning the unsuitability of

water flow patterns has the greatest support. Prefeeding mortality

has successfully been eliminated by the use of wooden upflow units.

Selection of a suitable food for larval striped bass includes

the consideration of particle size, stability of the food in water,

attractiveness to the larvae and, of course, nutritional balance.

Nauplii of the brine shrimp (Artemia) serve as an adequate diet

for the first six days of feeding, and as a supplemental diet for

an additional 14 days. The need for a diet intermediate between

brine shrimp and commercially prepared salmon feeds became apparent

in the 1975 study (Lewis and Heidinger, 1976). The use of fish

eggs as an intermediate diet may be successful. However, the

present study suggests that using an increased quantity -of brine

shrimp, along with a salmon starter which has been ground to flour

consistency, may eliminate the need for an intermediate diet.

Cannibalism was a primary contributor to the high rate of

early mortality in this study. However, maintaining high densities

of food in the water column should reduce the incidence of canni

balism. This indicates a need for a food which tends to remain

in the water column and is resistant to leaching.

Theories to explain the failure of larval striped bass to

inflate their swimbladders fall into two general categories.

Baker (1975) presents some evidence to support the theory that

this phenomenon may be genetic, while Bulak (1976) concludes that

the cause is environmental. Regardless of cause, fish lacking

swimbladders have a greater need for oxygen, either because of a

higher metabolic rate or a decreased ability to utilize available

oxygen.

To date, tank culture of fish has been most successful for

the salmonids. In the three years of work devoted to the present

method of tank culture of striped bass, the major problems which

limit its success have been identified and, except for specific

recommendations for insuring inflation of the swimbladder,

tentative solutions to the problems have been identified.

LITERATURE CITED

Baker, James F. 1975. The rearing of Hudson River striped bass at

the Edenton National Fish Hatchery, 1975. Report prepared for

Consolidated Edison Company of New York, Inc. 30 pp. mimeo.

Berg, Troud, and John Steen. 1968. The mechanism of oxygen concen

tration in the swimbladder of-the eel. J. Physiol. 195:631-638.

Bonn, E.W. (Senior editor). 1976. Guidlines for striped bass culture.

Striped Bass Committee. Southern Div. Amer. Fish. Soc. 125 p.

Bulak, James S. 1976. Investigations into the initial inflation of

the swimbladder in striped bass (Morone saxatilis). M.A. thesis.

Southern Illinois Univ. , Carbondale. 65 pp.

Kerlinger, F.N., and E.J. Pedhazer. 1973. Multiple regression in

behavioral research. Hol t, Rinehard and Winston, Inc. New York.

534 pp.

Lewis, W. M. , and R.C. Heidinger. 1976. Striped bass rearing experi

ments, 1975. Completion report submitted to Consolidated Edison

Company of New York, Inc. 89 pp.

Meade, Thomas L. 1974. The technology of closed system culture of

salmonids. Mar. Tech. Rep, 30. Univ. Rhode Island. 30 pp.

Minium, Edward W. 1970. Statistical reasoning in psychology and

education. John Wiley and Sons, Inc. New York. 465 pp.

Schwartz, Abby. 1971. Swimbladder development and function in the

haddock, Melanogrammus aeglefinus. Biol. Bull. 141:176-188.

Texas Instruments Inc. 1976. Feasibility of culture and stocking

Hudson River Striped Bass: 1975 Annual Report. Prepared for

Consolidated Edison Company of New York, Inc.

T A B L E S

Table 1.--Flush rates and water velocities. Striped 1976

Flush rate(gpm) Initial Final

Stage I Circular flow (tanks 1,2,10)

Modified upflow (tanks 1,2) Upflow (tanks 23,24) Upflow (tanks 25-32)

Stage II Circular flow (tanks 1,2,10,12-16) Circular flow (tanks 5-9)

Modified downflow (tanks 17,A)

Modified upflow (tanks 18,B)

Upflow (tanks 23,24)

2-3 2-3 2-3 2-3

4 5-7 4 4 4

2-3 2-3 2-3 5-7

15-20 15-20 15-20 15-20 10-15

bass inves tigations

Calculated velocity (inches per sec)

Initial Final

0 .0 2 -0 .0 4 a 0 .0 2 - 0 .0 4 a

0.11-0.17 0.11-0.17 0.02-0.02 0.02-0.02 0.02-0.02 0.04-0.05

0 .06a 0. 070 1 0 a

0.23 0.23 0.03

0 .21-0.28 0 .21 -0 .28a 0.85-1.13 0.85-1.13 0. 08-0. 11

aTangential velocity calculated at the perimeter of tetn Apni )the tank (Appendix 5).

Table 2.--Mortality of larval striped bass during shipping Striped bass investigations - 1976

and the first 24 hours after stocking.

Date Tank stocked Roe no. Box no.a Age at stocking Tempering time Bag mortality 24 hour mortalit, (hours) (min.) (no.) (no.)

13 May

18 May

Circular flow 1 2

Upf low 23 24 25 26 27 28 29 30 31 32

Mod. upflow 1 2

Upflow 25 26 27

Circular flow 1 2

Upflow 30 31 32 32

Circular flow 10

Up flow 29 31

12 5

1 6 4

10 2 7 3 8 9

11.

3 1.

2 5

64 64

64 64 64

81 81

81 81 81 81

142

142 142

750

750 20000

2000 3500

2000 2000 2000 2000 3000 2000 3000 2000 3000 2000

3000 2000

27000 1500 2000

1000 1000

1000 750

1000 750

9500 3000

2000 1000

6000

1500

1500 20000

aEach box contained approximately 100,000 striped bass larvae.

bShipping bag -broken.

5000 5000

3500 3500 4000 5000 5000 5000 5000 3000 4000 3000

10000 5000

30000 3000 3000

21 May

2 4 May

Table 3.--Stage II diets used in conjunction with brine shrimp nauplii. Striped bass investigations -1976

Age combination Age brine -Water flow started shrimp terminated

Tank type Food combination (days) (days)

1 Circular Silver Cup 13 24 2 it1 13 24

10 it Tetra-Min 13 24 12 if Silver Cup 9 26 13 if it a 26

14 "Tetra-Min 9 26 15 "Silver Cup 9 a 26 16 "Tetra-Min 9 26 17 Mod. downflow if 9 26 18 Mod. upflow Silver Cup 9 26 A Mod. downflow Tetra-Min 9 26 B Mod. upflow Silver Cup 9 26

23 Upflow If 8 26 24 it if 8 26 25 It Grindal worms 6 26 26 iit6 26 27 it Fish eggs 11 21 28 iit10 26

29 t15 24 3 0 b 15 24

31 15 24

3 2 b " 15 24

aSwitched to Abernathy's at 11 day old

bSecond stocking into these tanks

Table 4.--Survival of striped bass larvae under various types of rearing conditions. Striped bass investigations - 1976

Total fish harvested Receiving tank Fish stocked

Date Tank harvested (no.) Number Flow type (no.)

35,000

48,000

32,000

43,000

(partial harvest)

11,000 37,000

13,000 208

314 61

10,059

(removal of cannibals)

Ci r cula r

Down flow

Circular

Mod. upflow

Circular

8 Circular

Circular it

If

Circular 11

Circular of

Circular 11

If

20 May

21 May

10 June

15 June

20,000 15,000 20,000

1,000 20,000

7,000

15,000 17,000 10,000 29,000

2,000 2,000

10,000

11,000 9,000

20,000 8,000

13,000 208

344 61

18 June

20 June

24 June

27 June.

Table 5.--Survival of striped bass water flow conditions.a Stage I investigations - 1976

under various Striped bass

Water flow Days in system % survival

Circular flow 1 2 1 2

10

Modified upflow .1 2

Upf low 23 24 25 25 26 26 27 27 28 29 29 30 30 31 31 32 32

4 4 _b _b _b

3 3

_b

4 28 4

31 4

28 23,38

8 28 8

34 7

30 7

30

0 0

5.50 7.00 4.00

0 0

32. 96 18.00

0 37.00

7.00 13.00

0 11.00 10.06 32. 00 0.21

43.00 0.03

35. 00 0.16

48.00 0.03

a Due to 100% mortality, escapement, or harvest,

some tanks were stocked more than one time.

bTanks not harvested, estimate after 20 days.

Table 6.--Cause of mortality and estimated number of fish lost. Striped bass investigations - 1976

Cause No. fish lost % fish los

1 . Shipping mortality - Stage 1 202,000 7. 77

2. Water flow mortality in circular tanks - Stage 1 480,000 18.46

3. Escapement from upflow tanks - Stage 1 408,000 15. 69

4. Larval mortality - Stage I (unidentified cause) 518,000 19.92

5. Cannibalism Stage 1 560,000 21.54 Stage 11 83,000 3.19

6. Stocking mortality - Stage 11 165,0006.5

7. "20 day" mortality - Stage 11 6,500 0.25

8. "30-40 day" mortality -Stage 11 2,500 0.10

9. Escapement - Stage 11 10,000 0. 38

10. Water quality losses -Stage 11 3,400 0.01

11. Fish samples 12,000 0.46

12. Unaccounted 10 55 b 132,000 5.08

aEven though this is only 6.35 percent of the total striped bass stocked, this loss is approximately 73 percent of the fish that were alive and harvested after Phase I.

bflased on initial estimates of 2.6 million larvae striped bass.

Table 7.--Survival of striped bass fingerlings in eight circular tanks with various water flow patterns (Stage 11, 20 May 1976 through 12 August 1976). Striped bass investigations - 1976

Tank no. Flow No. of fish No. per No. of fish No. per Survival tank type stocked litera harvested litera M%

13 Circular 20,000 11.1 2040 1.1 10.2 14 Circular 15,000 8.3 841 0.5 5.6 15 Circular 30,000 16.7 2340 1.3 7.8 16 Circular 10,000 5.6 867 0.5 8.7

Average of circulars 18,750 10.4 1522 0.8 8.1

17 Downflow 20,000 11.1 756 0.4 3.8 A Downflow 20,000 11.1 2001 1.1 10.0

Average of downflows 20,000 11.1 1378 0.8 6.9

18 Mod. upflow 15,000 8.3 1078 0.6 7.2 B Mod. rupflow 19,000 10.6 1011 0.6 5.3

Average of mod. upflows 17,000 9.5 1044 0.6 6.1

aNo. per liter times 3.8 equals no.pe galnper gallon.

Table 8.--Results of the final harvest at completion of Stage 11 (12 August 1976). Striped bass investigations - 1976 (SC=Silver Cup, Ab-Abernathy's, TM=TetraMin)

Tank no. Water flow Diet No. fish No. fish Wt. harvested Survival type stocked harvested (kg) M%

Circular 11

Mod. downflow Mod. upflow Mod. downflow Mod. upflow

Up flow it

100,000 100,000

21,000 458

20,000 10,000 20,000

100,000 9,000

20,000 15,000 30,000 10,000 20,000 15,000 20,000 19,000

100,000 1005,00

1558 852

1994 431

1130 179 798 879

1129 2040

841 2340

867 756

1078 2001 1011

148 140

729,458 20,172

13. 58 8. 76

13. 89 9.41 8.40 2. 22 7. 98 9. 32

14. 48 20.14 8. 72

21.10 7. 80 8. 74

12.40 21.41 11.62

2. 86 2. 66

205.49

1.56 0. 85 9.50

94.10 5.65 1. 79 3.99 0. 88

12.54 10.20 5.61 7. 80 8. 67 3. 78 7. 19

10.00 5. 32 0.15 0.14

Table 9.--Percent of sampled fish 30 days and older with inflated swimbladders. Striped bass investigations -1976

Tank no. Roe no. % inflation Sample 30+ day old fish size

Circular 1 7 86.25 80 2 7 91.25 80 5 4 95.29 85 7 4 95.29 85 8 1 64.44 45 9 4 95.00 80

10 7 100.00 80 12 1 83. 33 90 13 1 81.11 90 14 1 100.00 90 15 1 87. 78 90 16 1 95.29 90

Mod. downflow .17 1 96.47 90

Mod. upflow 18 1 95.00 85

Mod. downflow A 1 94.44 90

Mod. upflow B 1 88. 89 90

Upf low 23 1 5 3 .8 5 a 65 24 1 7 5 .0 0 a 40

aCalculated from fish samples prior to the mortalities in tank 24 on 6 July and tank 23 onf 26 July. After these mortalities all fish sampled in both of these tanks had inflated swimb ladders.

Table 10.--Swimbladder inflation statistics during the Phase II water flow rearing conditions (weighted mean for fish 30 days and older). Striped bass investigations - 1976

Flow type Inflated swimbladders Sample M% size

Circular flow (13-16) 88.30 360 Modified upflow (18 and B) 92.04 175 Modified downflow (17 and A) 95.00 180 Control upflow (23 and 24) 6 3 .30 a- 105 Control circular flow (1 and 2) 88.02 160

aCalculated from fish samples prior to the mortalities in tank 24 on 6 July and tank 23 on 26 July.

Table ll.--Swimbladder inflation in relation to the Stage II diets (weighted mean for fish 30 days and older). Striped bass investigations -. 1976

Diet % inflated Sample swimbladders size

Abernathy's (tanks 13 and 15) 84.67 180 Silver Cup (tanks 18 and A) 94.64 175 TetraMin (tanks 14,16,17 and B) 94.82 360

LIn

Lin

Table 12.--Ranges of physiochemical parameters. Striped bass investigations - 1976

Tank Temp. 02 NH3 -N N02 -N N0 3-N pH M.O.A.

Hot-water

Input to circular tank

15.9-30.5

14. 9-28.0 6.0-10.8 0.04-1.85 0.011-0.210 0. 7- 6.9 7.50-8.53

Out flow of biofilters 1 15.0-27.0 2 15.0-27.0 3 15. 0-27.0 4 15.0-22.0

Mid-depth of 1 2 5 6 7 8 9

10 12 13 14 15 16 17 18 A B

2.2-11. 8 2.4-12.0 2.5-11.5 2.6-12. 4

circular tanks 15.2-28.0 3.2-11.8 15. 2-27. 0 3.8-11.7 20. 2-27. 0 3. 7- 7. 4 21.0-26.5 3.6- 7.5 20. 2-27. 0 3. 7- 7. 6 20.0-27.0 4.5- 7.7 20.6-27.0 3.7- 7.1 20.0-27.0 4.1- 8.0 19.0-27.0 3.8- 9.0 19.0-27.0 1.5- 8.8 19.0-27.0 3.4- 8. 7 19.0-27.0 3.1- 9.0 19.0-27.0 3.5- 9.1 19.0-27.0 3.5- 9.0 19.0-27.0 2.7- 8.9 19.0-27.0 2.8- 8.9 19.0-27.0 3.0- 8. 7

0.05-1.85 0.07-1.65 0.07-1. 70 0.07-1.60

0.05-1. 85 0.03-1.95 0.18-1. 75 0.19-1.95 0. 16-2.30 0.17-2.20 0.22-2.10 0.14-2.00 0.24-1.95 0.13-2.60 0. 18-2.40 0. 12-2.60 0.20-2.00 0.15-2.20 0.22-2.00 0.13-1.95 0.12-1. 77

0.009-0.210 0.009-0.210 0.008-0.210 0.007-0.210

0.015-0.210 0.011-0.250 0.048-0.240 0.049-0.220 0.048-0.230 0.037-0.220 0.062-0.220 0.013-0.220 0.015-0.210 0.016-0.210 0.015-0.210 0.016-0.210 0.015-0.210 0.018-0.230 0.015-0.240 0.017-0.230 0.018-0.230

1.0- 6.5 0.9- 5. 7 1.0- 6.5 0.8- 5. 7

1.0- 6. 8 0.8- 6. 3 1.2- 5.4 1. 7- 7. 8 1.6-11.5 1.5- 9.6 1.6- 9.8 0.*6- 9.6 0.9- 6.8 1.0- 6.8 0. 7-10.5 0.9- 5. 3 0.8- 6.6 1.2- 5. 8 0.9- 6.2 0.8- 6.0 0.8- 5.5

7. 35-8.45 7.40-8.44 7.20-8. 42 7.25-8. 57

7.50-8.56 7. 36-8.49 7.55-8. 35 7.54-8.29 7.52-8. 37 7. 63-8. 31 7.55-8.40 7.46-8.42 7.51-8. 40 7. 48-8. 41 7. 46-8.50 7. 42-8. 45 7.39-8.45 7. 39-8.42 7.40-8.44 7. 33-8. 48 7. 35-8.43

224-313

226-313 224-321 2 18-322 226-320

250-304 254-314 256-320 262-321 254-320 256-318 258-318 250-319 248-322 254-310 256-314 260-314 254-307 256-314 256-316 254-312 256-310

Table 12 (cont.)

Tank Temp. 02 NH 3 -N N02 -N N03 -N pH M.0.A.

Out flow of upflow tanks 23 15.0-27.0 2.9-11.2 0.12-2.30 0.013-0.220 0.8- 8.0 7.34-8.42 254-313 24 14.9-27.0 3.7-11.6 0.10-2.30 0.013-0.210 1.2- 6.0 7.30-8.55 256-318 25 15.2-27.0 5.0-11.5 0.22-0.55 0.011-0.022 0.2- 2.8 7.78-8.54 256-303 26 15.0-27.0 5.0-10.6 0.15-0.78 0.013-0.050 1.0- 3.5 7.64-8.42 256-303 27 15.0-27.0 5.3-11.5 0.18-0.63 0.015-0.048 0.8- 2.8 7.82-8.55 254-299 28 15.0-27.0 4.8-11.2 0.14-2.10 0.014-0.190 0.9- 3.5 7.57-8.48 256-301 29 14.7-27.0 4.4-11.2 0.17-0.98 0.015-0.068 0.8- 3.2 7.67-8.55 254-301 30 14.8-27.0 4.9-11.6 0.17-1.95 0.013-0.190 0.8- 3.3 7.51-8.50 256-310 31 15.0-27.0 4.5-11.4 0.05-0.93 0.013-0.070 0.9- 3.2 7.56-8.49 250-310 32 15.0-27.0 4.8-11.5 0.18-0.75 0.010-0.080 0.5- 3.5 7.58-8.50 250-309

F I

G U R E S

Fig. 1A A simplified flow chart of the various stocking and feeding regimes. Striped Bass Rearing Experiments 1976. Stage I

Fig. 1B A simplified flow chart of the various stocking and feeding regimes. Striped Bass Rearing Experiments 1976. Stage U

L = 12.2911 - 0.8588(A) + 0.0450(A 2 ) 0.0003(A 3 ) e

R 2 =0.9664 ee

0 too 5

4"o

oo].

10 20 30 40 50 60

AGE IN DAYS

70 s0 go

Fig. 2 Rate of growth of striped bass in all rearing units based on a total sample of 1,795 fish.

110901

30

20

60

120 IIII

0

o- MODIFIED UPFLOW 00 100-.- CIRCULAR FLOW0

0 80

0 "0

0 40 00

20

10 20 30 40 50 60 70 so 90 AGE IN DAYS

Fig. 3 Comparison of the growth rate of striped bass In modified upfilow (tanks 18 and B) and circular f low (tanks 13-16) during Stage IX22 May - 15 August, 1976.

(I) iUUru.1 901

o 801m U

60

(1) 50

Uj 40

( 30- 0ROEl1 UZ 20- *ROE 4

S10- AROE 7

0LI I I I 1 2 4 6 8 10 1214 16 1820 22 2426 2830

AGE IN DAYS

Fig. 4 Proportion of fish less than 30 days old with inflated swimbladders (based on roe number).

62

100- 0 6. 00 0 *e e 0

go0 - -~

Mi 0 so- @0

S70 / -j4/0

50zI

U. 40

Ir 30 ,

(L 20

10 I

10 20 30 40 50 60 70 80 90

AGE IM DAYS

Fig. 5 Time of swimbladder Inflation of striped bass in all rearing units based on a totalI sam ple of 2,090 f ish.-

A P P E N

63

Appendix 1. Feeding schedule striped bass investigations - 1976 (BSE = Brine shrimp eggs; SC ST., SC1 SC2, SC3 = Silver Cup diet of various sizes; Ab = Abernathy salmon starter; TM = TetraMin; FE = Fish eggs; GW =Grindal worms)

Tank no. Diet and rate Dates utilized (grams per day)

134.5 BSE 22 May - 29 May 51.6 "+ 60 ground SC ST. 30 May - 1 June 51.6 "+ 120 it 2 June - 4 68. 9 "+ 120 SC ST. 5 " - 6 189. 9 "+ 120 if 7 " - 10 240 ground SC ST. 11 " - 18 120 it it + 120 SCi 18 " - 20 120 SCi 21 " - 25 240 it 26 " - 3 July

360 if 4 July - 13 240 it + 240 SC2 14 " - 19 360 SC2 + 120 SC3 20 " - 3 Aug 120 5C2 + 120 " 4 Aug - 12 "

2 (identical to tank 1) (22 May - 3 July) 240 SCl 4 July - 13 120 "1 + 120 SC2 14 1" - 18 120 SC2 + 240 SC3 19 it - 3 Aug 100 It + 200 " 4 Aug - 12 "

5 120 g round SC ST. 15 June - 21 June 120 SCl 22 - 3 July 360 of 4 " - 13 360 "1 + 120 SC2 14 July - 18" 240 SC2 + 120 SC3 19 it - 3 Aug 120 if + 120 "4 Aug - 12 "

6 120 SCl 20 June - 25 June 240 SC2 26 11 - 3 July 360 it 4 July - 18 " 300 "+ 240 SC3 19 "1 - 3 Aug 360 SC3 4 Aug - 12 "

7 240 ground SC ST. 15 June - 21 June 120 SCl 22 11 - 3 July

360 if 4 July - 13 360 "1 + 120 SC2 14 " - 18 360 SC2 + 120 SC3 19 " - 3 Aug 120 SC2 + 120 SC3 4 Aug - 12 "

Appendix 1 (cont.)

Tank no. Diet and rate Dates utilized (grams per day)

120 ground SC ST. + 200 ml FE 240 itf120 SCl 240 It + 120 SC3

240 ground 240 SCi 360 i

360 it +

240 SC2 + 120 If +

34.5 BSE 51.6 "+ 51.6 "+ 68.9 "+ 189.9 "+ 240 ground 120 i

120 SCi 240 o

120 if +

240 SC2 + 120 "+

34.5 BSE + 68.9 " + 120 ground 240 Ab ST. 360 Ab 2/64 360 It

300 it

240" 720 Ab 3/64 560 " o

120 SC2

SC ST.

120 SC2 120 SC3 120 1

60 ground 120 i

120 i 120 i

TM SC ST.

120 SC2 120 SC3 120

60 ground 120 i

SC ST.

+ 120 Ab + 300 + 480

34.5 BSE + 60 groun-d 68.9 " + 120 if

120 ground Ab ST. 240 Ab ST. 360 Ab 2/64 360 if" + 120 Ab 300 if" + 300 " 240 " It + 480 " 720 Ab 3/64 560 " i

SC ST. if

3/64 of

if

Ab ST. 11

3/64 it

if

J un e

July 11

J un e

July 11

Aug

May May June

it

July it

it

Aug

May June

It

it

it

it

it

it

it

Aug

May June

it

if

it

If

July if

if

Aug

June it

July It

Aug

J un e July

It

it

Aug if

May June

it