Improvements in swimbladder Improvements in swimbladder inflation in yellowtail kingfish inflation in yellowtail kingfish

((Seriola lalandiSeriola lalandi) larvae) larvae

Lindsey WoolleyFlinders University

Supervisors:A/Prof. Jian QinDr Bennan Chen

Wayne Hutchinson

Problem

Cleans Seas Tuna production > 1 million YTK fingerlings per year

Currently ) 10 % larval survival rates

High swimbladder malformations per production run 0-60 days post hatch (dph)

Failed inflation = Decreased survivability in larval rearing

Introduction Swimbladder internal gas-filled sac, contributes to

the ability of a fish to maintain neutral buoyancy

Flexible-walled organ found dorsally below the notochord

Impermeable to gas: poorly vascularized and lined with a sheet of guanine crystals

Swimbladder of a rudd (Scardinius erythrophthalmus)

7 dph larvae without swimbladder inflation

Failed initial inflation

Linked to abiotic factors

Abnormal development, liquid dilated swimbladder collapses with hypertrophy of epithelium

Swimbladder malformationSwimbladder malformation

Why is swimbladder malformation Why is swimbladder malformation detrimental?detrimental? Decreased survival

higher mortality under stress

Delayed growth fish with no functioning swimbladder are 20-30% smaller in weight

than normal fry

Skeletal deformities occurrence of lordosis (curvature of the 2nd and 3rd vertebrae)

Metabolic demands higher abnormal larvae have buoyancy abnormalities higher energy requirements to maintain normal swimming

behaviour

= reduced production performance

Project objectives

Increase swimbladder inflation rates of YTK larvae (< 2 % malformation)

Determine body density and distribution of larvae in rearing tanks

Determine abiotic factors that promote optimum swimbladder inflation

Increase overall survival rates to 25 % by 2011

Research plan

Develop a standardized protocol to assess swimbladder inflation use of anaesthetics compromises swimbladder

volume

Describe larval swimbladder development morphology and histological assessments

(0 - 10 dph)

Determine effect of swimbladder inflation on body density and larval distribution within rearing tanks density and distribution studies

1. Swimbladder and body density assessment

Research plan2. Abiotic factors

Investigate effects of surface skimmers Skimmers remove oil from water surface Allow larvae to gulp air at the surface for

initial inflation

Photoperiod Natural vs. artificial (halogen) light Various photoperiod light regimes

Temperature 20 – 25 °C

Research plan3. Commercial validation

Assess YTK swimbladder malformation in weaned larvae CST Arno Bay Hatchery 40 dph YTK

Determine consequences of YTK swimbladder malformation on grow-out CST Arno Bay sea cages Fingerling – juvenile (5 g - 500 g)

Validate findings with Southern bluefin tuna (SBT, Thunnus maccoyii) larvae Describe swimbladder development in SBT Investigate effect of abiotic factors on

swimbladder inflation rates

0 – 2 days post hatch

Forms as an envagination of the digestive tract

Lumen increases in size

Epithelium cells decrease in thickness to allow for dilation

Rete mirabile develops as fine capillaries

Lumen is liquid-filled at this stage

ResultsYTK swimbladder development

3 – 5 days post hatch

Inflation occurs within a discrete window between 3 – 5 dph

Liquid- filled bladder becomes inflated with air … ? process is still not understood properly

Gas gland develops at the anterior pole, composed of squamous epithelium

Rete mirabile increases in complexity – functions as a countercurrent exchanger

Critical period for Critical period for swimbladder inflationswimbladder inflation

Post larval stage Reared in hatchery (0 -40 dph)

3.5 g

Reared in nursery (40 – 60 dph) 3.5-5 g

Grow-out in sea cages (>5 g)

7 dph larvae with an inflated swimbladder9 dph larvae with

collapsed swimbladder

8 dph larvae with inflated swimbladder

Fish with non-inflated swimbladdersFish with inflated swimbladders

Specific gravity With inflation: 1.022 g cm-3

Without inflation: 1.030 g cm-3

MANOVA: P< 0.001

2 dph liquid-filled

Swimbladder

Initial Inflation

Body density change with growth

Inflation failure = sinking death syndrome (10 – 15 dph)

An increase in bladder volume = larvae are less dense then their environment and rise to the surface

Commercial applicationsCommercial applications

Increase the rate of swimbladder inflation, contributing to the overall increase in larval survival rates

Define a standard protocol for swimbladder assessment at 3 – 5 dph larvae

Define the range of abiotic factors that promote optimal swimbladder inflation

Compare the swimbladder development between YTK and SBT

Increase production of YTK larvae to a 25 % survival rate by 2011

Acknowledgements Australian Seafood Cooperative Research Centre“This work formed part of a project of

the Australian Seafood Cooperative Research Centre, and received funds from the Australian Government’s CRCs Programme, the Fisheries R&D Corporation and other CRC Participants”.

Flinders University • A/Prof. Jian Qin

SARDI-Aquatic Sciences • Dr Bennan Chen • Wayne Hutchinson

Clean Sea Tuna Ltd. Arno Bay Hatchery • Mike Thomson • Alex Czypionka

Hatchery system images courtesy of Paul Skordas

(SARDI Hatchery)