Aquaculture, 50 (1985) 61-73 61 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

FORMULATION OF PRACTICAL DIETS FOR RAINBOW TROUT (SALMO GAIRDNERI) MADE BY PARTIAL OR COMPLETE SUBSTITUTION OF FISH MEAL BY POULTRY BY-PRODUCTS AND CERTAIN PLANT BY-PRODUCTS

MARIA N. ALEXIS’ , ELLI PAPAPARASKEVA-PAPOUTSOGLOU’ and VASILIKI THEOCHARIZ

’ National Centre for Marine Research, GR-166 04 Elliniko (Greece)

‘National Hatchery of Louros, Hani Terovou, Ioannina (Greece)

(Accepted 19 June 1985)

ABSTRACT

Alexis, M.N., Papaparaskeva-Papoutsoglou, E. and Theochari, V., 1985. Formulation of practical diets for rainbow trout (SaEmo gairdneri) made by partial or complete sub- stitution of fish meal by poultry by-products and certain plant by-products. Aqua- culture, 50: 61-73.

Rainbow trout of approximately 20 g initial average weight were fed seven exper- imental diets and a commercial diet for 197 days. All experimental diets had the same proximate composition and were formulated by partial or complete substitution of fish meal by poultry by-products in combination with certain plant by-products. The plant by-products were soybean meal, carob seed germ meal and corn gluten meal. Linseed oil was used in order to increase the fat content of the diets and to supply the indispensable fatty acids. Diets containing soybean meal and corn gluten meal gave the best results, comparable to those obtained with the commercial food. Results obtained from the diets containing carob seed germ meal were inferior, especially during the first 50 days of rearing. Haematological characteristics of all fish tested were within the normal values reported in the literature. Liver composition did not indicate any lipid or glycogen accumulation. The results of growth and food conversion are discussed in relation to the cost of production calculated for each diet.

INTRODUCTION

One of the main factors contributing to the total cost of production of cultured fish is the price of their food. The food used in Greece for cultur- ing rainbow trout is mainly imported, so that the price is high and is subject to currency fluctuations. For that reason a research programme was initiated by our Centre with the objective of developing optimal rainbow trout feeds, using mainly local by-products.

This paper presents results obtained after feeding rainbow trout, from the average weight of 20 g up to the commercial weight, with practical diets

0 1985 Elsevier Science Publishers B.V.

62

fo~ulated by partial or complete substitution of fish meal by poultry by- products and certain plant by-products. Poultry by-products, available in the local market, were used as one of the main protein sources in all diets tested. Soybean meal, carob seed germ meal and corn gluten meal were used alone or in combination for partial or total substitution of fish meal.

Fish growth, body composition, haematological and liver characteristics as well as cost of production are presented and discussed.

MATERIALS AND METHODS

At the National Hatchery Station, Louros, rainbow trout fry, having an average weight of 2.3 g each, were divided into 11 groups of 150. They were maintained in 1.5 X 0.7 X 0.8 m cages. The cages were held in concrete raceways where the water flow rate was 1.5 l/s, water temperature was ll”-13”C, pH 7.4-7.8, conductivity 235-265 pMhos/cm and hardness 220-260 ppm CaCO, .

All fish were initially fed with a commercial diet at a rate of 5% of their body weight per day. After 85 days each group was reweighed and of the 11 groups, the 8 which exhibited similar growth were used for the exper- iment. The initial mean weight of the fish is given in Table 3.

Seven diets were formulated and one was assigned to each cage. A com- mercial food was also used for comparison. The proximate composition of the ingredients used in the formulation of the diets is given in Table 1. The composition of each of the diets, as well as the cost per kg is given in Table 2. All diets were formulated so that their proximate composition, in basic nutrients and gross energy, was almost the same.

The nutritional value of carob seed germ meal (CSGM, Ceratoniu siliqua), tested in rats, was found to be similar to that of soybean meal (Drouliskos and Malefaki, 1980), while its cost per kg was approximately half. CSGM was included in diets 3 and 5 in a proportion that contributed amounts of

TABLE 1

Proximate composition of the ingredients used in the various diets (%)

Ingredient Protein Lipids Moisture Ash Fibre Nitrogen free extract

Fish meal 66.1 11.0 5.4 16.3 1.2 Poultry by-products 65.9 15.3 10.7 7.1 1.1 Corn gluten meal 60.6 11.5 6.9 1.5 1.4 18.2 Soybean meal 50.1 1.5 9.7 7.0 7.5 24.2 Carob seed germ meal 44.1 4.8 5.4 9.0 3.8 33.1 Wheat middlings 14.1 4.5 12.0 4.0 9.0 56.4 Corn 7.8 3.9 12.0 1.3 3.5 71.3 Bone meal 2 98.0

63

TABLE 2

Formulations ($7~ composition), proximate analyses (96 weight composition), energy contents and cost per kg of experimental diets (l-7) and a commercial diet (8)

Diet

1 2 3 4 5 6 7 8

Formulation (W dry weight)

Herring meal Poultry by-product Soybean meal Carob seed germ meal Corn gluten meal Wheat middlings corn Bone meal Methionine Lysine Linseed oil Vitamin premix a Mineral premix b Choline chloride (50%)

57

21 13

35 27.5 29.9

1.2 0.1 0.6 1

0.7

6.8 6.4 6 7.5 0.08 0.08 0.08 0.08 0.2 0.2 0.2 0.2 0.6 0.6 0.6 0.6

20 25 12

20 25

20

10

25 25

10 25 35

35 35

20.7 20.2

1.1 1 0.5 0.1 0.2 1.1 6.6 6.1 0.08 0.08 0.2 0.2 0.6 0.6

30

12 20 27.9

1.4 0.5 2 5.3 0.08 0.2 0.6

Protein Fat Moisture Ash Fibre Nitrogen-free

extract Gross energy

(kcal/kg diet) c Gross protein

to energy ratio d Cost per kg

of food (Dr) e

Proximate analysis (W)

42.9 41.1 42.9 13.2 13.6 13.8

7.9 10.3 9.1 10.3 1.2 7.9

2.4 4.4 3.6

23.3 23.5 22.8

4624 4565 4660

92.6 90.1 91.7

68.71 51.45 41.43

40.5 43.0 43.3 43.4 45.4 13.5 14.0 13.7 13.6 8.0 10.4 8.0 9.1 9.8 11

1.3 7.5 1.4 5.9 14.2 4.9 3.5 3.5 3.6 2.7

23.5 24.1 23.1 23.4 18.7

4735 4684 4707 4088

90.9 92.6 92.6 111.1

42.3 42.5 49.5 60

4523

89.3

50.06

a Composition of vitamin premix expressed as mg per kg of finished feed except where otherwise indicated: thiamine 10, riboflavin 20, pyridoxlne 10, calcium pantothenate 40, nicotinic acid 150. biotin 1, folic acid 5, vitamin B,, 0.02 inositol 40, vitamin A 2500 i.u.. vitamfn D, 500 i.u., vitamin E 60 i.u.. vitamin K, 5. ascorbic acid 400. b Composition of mineral premix. A commercial mixture of minerals (Suivit) was used, fortified with AlCl, *6H,O, KI and CoCl, ‘6H,O to contain in mg/2 g mixture: Fe 200, Al 0.3, Zn 300. Cu 200. Mn 63. I 5.3. co 7.3. c Based on 5.65 kcal/g protein, 9.45 kcal/g fat and 4.1 kcal/g carbohydrate. d mg protein/caL e Cost of by-products plus an estimate of the cost of feed production.

protein (19.9% and 35.6% respectively of the total protein) about equal to those contributed by soybean meal in diets 2 and 4 (14.7% and 31% re- spectively). Its nutritional value for rainbow trout could thus be compared to that of soybean meal.

Linseed oil was used for increasing the oil content of the diets to about 14% since a high fat content had been found to be beneficial for rainbow trout growth (Lee and Putnam, 1973; Watanabe et al., 1979). The reason for preferring linseed oil to the commonly used fish oil is that it is a local product (while fish oil could not even be found in the local market), with a high content in linolenic acid, which is an indispensable fatty acid for rainbow trout (Caste11 et al., 1972a; Takeuchi and Watanabe, 1977). The

64

ingredients were mixed and the feed was prepared by compression through a pelleting machine. Linseed oil was sprayed on the pellets immediately after their preparation.

Fish were fed, at a daily rate of about 2% of their body weight, three times a day, seven days a week. The whole population of each cage was weighed every fortnight. Fish were starved for 24 h before each weighing. After 150 days the fish were released from the cages into the raceways (dimensions 6 X 1 X 1.2 m) and remained there until they had grown to commercial size. The experiment lasted from 7 September 1983, to 21 March 1984.

A sample of 10 fish was removed from each cage after 49 days of rearing as well as at the end of the experiment (197 days of rearing), for crude constituent analysis. Fish were killed by a blow on the head and blood removed from the caudal artery for haematocrit and plasma constituent determination. Haematocrit was determined by using heparinized, pre- calibrated, haematocrit tubes and centrifugation in a Clay-Adams Readacrit Centrifuge. Plasma glucose was measured by the glucose oxidase method, cholesterol by the cholesterol oxidase method, lipids by the phosphovanil- lin method (Boehringer kits no. 124018, 237574 and 124303 respectively) and protein by the Lowry method (Lowry et al., 1951).

Livers were removed, weighed for hepatosomatic index determination and analysed for moisture, protein and ash by standard procedures (AOAC, 1975). Glycogen content was measured by the method of Murat and Serfaty (1974) and lipids by the phosphovanillin method, after a small part of tissue had been solubilized in concentrated sulphuric acid by heating in a boiling water bath. When this method was compared with the commonly used method of Folch et al. (1957) no significant differences were apparent. (Average values obtained for the same liver were 3.56 + 0.15 by the Folch method and 3.72 + 0.25 by the phosphovanillin method).

Fish were minced, lyophilized and their composition determined by the same methods used for determining liver composition, with the exception of lipids, which were determined by Soxhlet extraction. Comparisons of the averages were made by using Student’s t test (Youden, 1951).

RESULTS

The growth of the fish is presented in Fig. 1. Growth up to a weight of about 90 g is also presented in a more detailed form. Performance factors and body composition of the fish, after the initial period of 49 days of experimental feeding and for the whole rearing period (197 days), are presented in Tables 3 and 4 respectively.

Groups fed with diets 2, 4, 7 and the commercial food (8) exhibited similar growth patterns throughout the growing period, although the group fed with commercial food showed a somewhat retarded growth rate during the last month of the experiment. Groups fed with diets 1, 3 and 5 exhibited

65

100,300-

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-250.

70- -

60. .

50.2oc-

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fish growth for the first 100 days of rearing in greater detail.

66

TABLE 3

Performance and body composition of rainbow trout fed experimental (l-7) and commercial (8) diets for 49 days

Diet

1 2 3 4 5 6 7 8

Initial weight 20.6 23.5 23.8 23.8 23.1 19.8 20.2 20.9 of fish (9)

Performance factors Weight gain (9) 34.2 43.1 32.0 43.2 29.5 28.0 34.5 34.6 Feed conversion 1.36 1.18 1.52 1.16 1.59 1.42 1.29 1.30 Dress-out weight (%) 87.2 86.2 85.4 86.1 86.6 86.0 88.0 87.9

Proximate analysis (%) Crude protein 15.2 b 15.4 b 14.7 a 15.3 b 14.7 a 14.6 a 15.2 b 15.1 b Crude fat 7.1 b 8.1 d 7.4 c 7.9 d 7.5 c 6.9 ab 8.0 d 6.8 a Ash 2.5 a 2.5 a 2.6 a 2.7 a 2.5 a 2.5 a 2.5 a 2.6 a Moisture 75.1 d 73.8 ab 74.7 c 74.1 b 74.6 c 75.6 e 73.7 a 74.7 c

Along each row values followed by the same letter are not significantly different

intermediate growth while diet 6 gave the slowest growth of all. During the first 49 days of the experiment, diets 2 and 4 resulted in the lowest food conversions, diets 7 and 8 were intermediate, while diets 1, 3, 5 and 6 showed the highest food conversions. At the end of the experiment feed conversions were better for diets 2, 4 and 7 and higher for all the rest. How- ever the differences among the final food conversions were smaller than the differences observed during the earlier rearing period. It appears therefore, that the differences in size among the dietary groups, at the end of the ex- periment, resulted from differences in food conversion and growth during the first period of feeding, combined with the restricted food intake regime (in proportion to the fish body weight) used in the experiment.

Protein productive values (PPV), of the diets tested, are within the ranges reported for commercial foods (Pfeffer, 1982). Diets 2, 4 and 7 gave the highest PPVs, while the commercial diet had the lowest one, possibly due to its higher protein and lower lipid content.

Diet 1, which contained fish meal as the sole protein source gave results inferior to most of the other experimental diets. The same was observed in other experiments in which the effectiveness of similar diets to smaller fish was tested (unpubl.). A better performance of fish when the fish meal contained in their diets was partially substituted by poultry by-products has also been reported by others (Gropp et al., 1979).

For fish kept on the same diet, average body fat increased as the weight of the fish increased, while ash and moisture content decreased; this is accord- ance with other studies (Reinitz, 1983). Feeds containing CSGM resulted in fish with significantly lower protein content than the rest of the groups at the end of the first period of rearing (diets 3, 5 and 6 Table 3), while no such difference was apparent at the end of the experiment. Fish receiving experimental diet8 had similar protein contents at the last sampling with the

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69

exception of fish receiving diets 6 and 7. Lipid content was more variable. The differences in the final body composition cannot be attributed to a single factor since many parameters known to affect body composition come into play, such as fish weight, nutritional history and degree of matura- tion (Papoutsoglou and Papaparaskeva-Papoutsoglou, 1978; Reinitz, 1983). In this experiment certain male fish were found to be precociously mature.

Haematological characteristics, given in Table 5, were generally within the range of normal values reported in the literature (Hille, 1982; McCarthy et al., 1973, 1975). Haematocrit values were not significantly different between the first and the second sampling, for fish belonging to the same group, except for the group which received diet 2; this had a significantly higher haematocrit value at the second sampling. Groups which received diets 2, 4 and 7 had, at both samplings, high haematocrit values significantly different from most of the other groups. The group of fish receiving the fish meal diet also had a high haematocrit value. Fish fed the commercial food had significantly lower haematocrit values than all other fish at the second sampling.

At the first sampling, fish receiving the commercial diet had significantly lower plasma lipids than other fish, apart from fish grown on feed 5. The same was apparent for cholesterol levels. Plasma lipids and cholesterol

TABLE 6

Liver composition of rainbow trout (% of tissue weight)

Diet Moisture Protein Glycogen Lipids Ash Hepatosomatic a index

First sampling (49 days of rearing) 1 73.8*1.0 18.2t1.2 1.7 to.5 3.5iO.3 1.46*0.09 1.18kO.20 2 72.9il.l 18.2t1.2 3.9 i0.9 2.3~0.2 1.49tO.14 1.22+0.17 3 72.2kl.O 2O.Ot1.4 2.3 50.6 3.7tO.3 1.69+0.09 1.15kO.19 4 73.2kO.6 18.4k1.3 3.5 kO.9 3.7fO.5 1.38tO.13 1.29kO.25 5 73.4fO.7 18.6rl.O 3.0 eO.8 3.3kO.4 1.5OkO.05 1.20+0.18 6 72.2kl.O 19.4+0.8 2.4 ~0.6 3.120.2 1.7620.09 1.19+0.17 7 73.4il.l 18.1kO.9 3.5 il.1 3.7iO.4 1.4420.11 1.23fO.20 8 74.7~1.0 17.7+0.5 3.5 t1.0 3.5tO.2 1.42+0.11 1.39t0.48 Average 7 3.3 18.5 2.9 3.4 1.53 1.23

Last sampling (197 days of rearing) 1 75.1r0.8 17.7iO.9 3.0 f0.8 3.3rO.l 1.62kO.10 1.09f0.14 2 74.OeO.5 18.9kO.6 2.4 to.7 3.9kO.4 1.56kO.07 l.ll+O.lO 3 73.5* 1.1 18.3~1.0 1.9 to.6 3.4fO.4 1.51cO.08 1.04kO.15

4 74.7r0.8 18.5*1.0 2.5 +l.O 3.450.4 1.52iO.06 1.06*0.16 5 73.9to.9 18.8kO.7 3.0 +0.8 3.4+0.3 1.52kO.04 0.96iO.13 6 74.2tO.5 19.0t0.8 2.3 to.9 3.OkO.2 1.5820.06 0.96kO.13

7 73.8tO.6 18.4r0.4 2.9 to.9 3.1to.3 1.55kO.04 0.89+0.13 8 74.3fO.8 18.9tO.8 2.3 50.6 3.5tO.3 1.56tO.06 1.18+-0.19 Average 74.2 18.4 2.6 3.4 1.56 1.04

aWeight of the liver x loo/weight of the fish.

70

levels decreased si~ific~tly at the second sampling for all groups except those receiving diets 5 and 8. Diets 3 and 6 produced fish with the lowest lipid and cholesterol plasma content at the second sampling. It appears that the diets containing a considerable amount of CSGM resulted in lower glucose values than those obtained from other groups except the commercial food.

Hepatosomatic index and liver composition at both samplings are given in Table 6. Hepatosomatic index for fish kept on the same diet tended to decrease with the size of the fish and this is in accordance with other studies (Dendon and Yousef, 1976). The moisture content of the livers appears to have been significantly higher at the second sampling for most of the groups, while protein and lipid content did not seem to change appreciably. No consistent change was obvious for glycogen and ash values between the first and second sampling. The glycogen content of livers was generally low compared with that in fish receiving high amounts of digestible carbohy- drates (Bergot, 1979; Hilton and Slinger, 1983). Lipid contents were also low as compared to those of fish receiving diets deficient in essential fatty acids (Caste11 et al., 1972b). It therefore appears that the diets used here contained suitable levels of carbohydrates, and were balanced in essential fatty acids.

DISCUSSION

The inferior performance of the fish receiving the CSGM containing diets compared with that of groups receiving soybean meal is possibly a result of the lower availability of nutrients contained in the CSGM diets. Preliminary measurements of the digestibility of some of the by-products used here, performed in this laboratory by the stripping method, gave a value of about 80% digestible protein for fish meal and soybean meal, 60% for poultry by-products and 50% for CSGM. On the basis of these values, the digestible protein content of diets containing soybean meal (2, 4) is about 30%, while that of diets containing CSGM (3, 5, 6) ranges from 29% to 26%.

The digestible energy content of the diets containing CSGM was, again, slightly less than that of the diets containing soybean meal, when an average digestibility of 85% for lipids and 40% for carbohydrates is used for the calculation (Ph~~ps and Brockway, 1959). These differences are not suf- ficiently large to explain, alone, the large differences in growth and food conversion observed in the first period of rearing. Digestibility studies were performed with fish weighing 150-200 g while the differences in growth were noted for fish growing from 20 g to 60 g. It might therefore be argued that fish of smaller size are less able than larger fish, to use CSGM. This view is supported by the fact that overall food conversions are not much different.

The similar overall food conversion, when considered in relation to the lower price/kg of food of the CSGM-containing diets, resulted in a much lower cost of production/kg of fish (Table 4), especially for diets 5 and 6.

71

It therefore appears ‘that these diets could be successfully used for growing fish from about 60 g to the commercial size with a considerable reduction of the cost of production, since 3/4 of the food is consumed during this growing period. More experiments are currently in progress in order to assess the nutritional value of CSGM for rainbow trout of different sizes and to test methods for its better utilization.

Feed 7 appeared to give the best results as far as fish growth, flesh qual- ity and protein productive values are concerned, with an intermediate cost of production. Satisfactory results after a 25% substitution of fish meal protein by corn gluten meal in trout ratios have been also reported by Gropp et al. (1979). Corn gluten meal could also support a growth equal to that obtained with herring meal when used as the sole protein source in rainbow trout rations, when the diet is supplemented with certain amino acids, mainly lysine (Ketola, 1982).

The retardation of growth, during the last month of rearing, of the group of fish which received the commercial diet might be due to a reduction in the vitamin content of the diet. This is supported by the fact that haemato- crit levels of the fish in this group were significantly lower, at the end of the experiment, than those of almost all other groups of fish. Vitamin de- struction, in commercial feeds for fish, is a problem frequently encountered when feeds are stored for a long time before use.

The decrease, found here, in the plasma lipid and cholesterol levels with size is contrary to reports that these levels increase with the weight of the trout (Hille, 1982). This discrepancy might be the result of an inability of the fish to adjust to the high lipid content of the diet during the first period of feeding. The decrease was not observed only in the group which received the commercial food throughout, i.e. the only group in which the diet was not changed at the start of the experiment.

The contribution of the lipid composition of the diets to the experimental results needs to be considered. Linolenic acid satisfies the essential fatty acid requirements of rainbow trout, at a level of 20% of the dietary lipids, when used in combination with a saturated fatty acid (Takeuchi and Watanabe, 1977). The requirements for linolenic acid, to achieve optimum growth and food conversion appear, however, to be different when w6 or w6 and wl fatty acids are included in the diet (Yu and Sinnhuber, 1975, 1976). Fatty acids from the lipids of poultry by-products and from linseed oil are the main contributors to the fatty acids of the diets tested here (at about 30% and 45% respectively); consequently the content in these diets of w6 and wl fatty acids is high. The level of linseed oil that would, therefore, give the best results in diets of this type needs to be further examined. However, the lower cost of production per kg of fish produced, ranging from 70 to 85% of that of the commercial food, together with the normal appearance of the fish, indicates that all the diets tested could be successfully used, in practice, for growing fingerling rainbow trout to the commercial size. The decision as to the particular diet to be used would be based on the specific

72

needs of each producer, depending on whether he would need to keep feeding costs to the minimum or to reduce expenses on labour and require- ments in water and holding space, since the diets that would provide a faster growth (e.g. diets 2 and 7) generally result in a higher cost of food per unit of product, compared to those giving a slower growth (like 5 and 6).

ACKNOWLEDGEMENTS

We wish to thank Mr M. Filioglou and Miss M. Galani for their valuable assistance with the samplings, and Mr G. Nanos for the care and feeding of the fish.

REFERENCES

Association of Official Analytical Chemists (AOAC), 1975. Official Methods of Analysis. AOAC, Washington, DC, pp. 927-928.

Bergot, F., 1979. Carbohydrate in rainbow trout diets: effects of the level and source of carbohydrate and the number of meals on growth and body composition. Aqua- culture, 18: 157-167.

Castelf, J.D., Sinnhuber, R.O., Wales, J.H. and Lee, D.J., 1972a. Essential fatty acids in the diet of rainbow trout (Salmo gairdneri): growth, feed conversion and some gross deficiency symptoms. J. Nutr., 102: 77-85.

Castell, J.D., Lee, D.J. and Sinnhuber, R.O., 1972h. Essential fatty acids in the diet of rainbow trout (Salmo gairdneri): lipid metabolism and fatty acid composition. J. Nutr., 102: 93-100.

Denton, J.E. and Yousef, M.K., 1976. Body composition and organ weights of rainbow trout, Salmo gairdneri. J. Fish Biol., 8: 489-499.

Drouliscos, N.J. and Malefaki, V., 1980. Nutritional evaluation of the germ meal and its protein isolate obtained from the carob seed (Ceratonia siliqua) in the rat. Br. J. Nutr., 43: 115-123.

Folch, J., Lees, M. and Sloane Stanley, G.H., 1957. A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem., 226: 497-509.

Gropp, J., Koops, H., Tiews, K. and Beck, H., 1979. Replacement of fish meal in trout feeds by other feedstuffs. In: T.V.R. Pillay and Wm.A. Dill (Editors), Advances in Aquaculture. Fishing News Books, Farnham, England, pp. 596-601.

Hille, S., 1982. A literature review of the blood chemistry of rainbow trout, Sa~mo gairdneri Rich. J. Fish Biol., 20: 535-569.

Hilton, J.W. and Slinger, S.J., 1983. Effect of wheat bran replacement of wheat middlings in extrusion processed (floating) diets on the growth of juvenile rainbow trout (Salmo gairdneri). Aquaculture, 35: 201-210.

Ketola, H.G., 1982. Amino acid nutrition of fishes: requirement and supplementation of diets. Comp. Biochem. Physiol., 73B: 17-24.

Lee, D.J. and Putnam, G.B., 1973. The response of rainbow trout to varying protein/ energy ratios in a test diet. J. Nutr., 103: 916-922.

Lowry, O.H., Rosenbrough, N.J., Farr, A.L. and Randall, R.J., 1951. Protein measure- ment with the Folin phenol reagent. J. Biol. Chem., 193: 265-2’75.

McCarthy, D.H., Stevenson, J.P. and Roberts, M.S., 1973. Some blood parameters of the rainbow trout (Satmo gairdneri Richardson). I. The Kamloops variety. J. Fish Biol., 5: l-8.

McCarthy, D.H., Stevenson, J.P. and Roberts, M.S., 1975. Some blood parameters of the rainbow trout (Salmo gairdneri Richardson). II. The Shasta variety. J. Fish Biol., 7: 215-219.

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Murat, J.C. and Serfaty, A,, 1974. A simple enzymatic determination of polysaccharide (glycogen) content of animal tissues. Clin. Chem., 20: 1576-1577.

Papoutsoglou, S.E. and Papaparaskeva-Papoutsoglou, E., 1978. Comparative studies on body composition of rainbow trout (Salmo gairdneri R.) in relation to type of diet and growth rate. Aquaculture, 13: 235-243.

Pfeffer, E., 1982. Utilization of dietary protein by salmonid fish. Comp. Biochem. Physiol., 73B: 51-57.

Phillips, A.M., Jr. and Brockway, D.R., 1959. Dietary calories and the production of trout in hatcheries. Progr. Fish CuIt., 21: 3-16.

Reinitz, G., 1983. Relative effect of age, diet and feeding rate on the body composition of young rainbow trout (Salmo gairdneri). Aquaculture, 35: 19-27.

Takeuchi, T. and Watanabe, T., 1977. Dietary levels of methyl laurate and essential fatty acid requirement of rainbow trout. Bull. Jpn. Sot. Sci. Fish., 43: 893-398.

Watanabe, T., Takeuchi, T. and Ogino, C.H., 1979. Studies on the sparing effect of lipids on dietary protein in rainbow trout. (Salmo gairdneri). In: J.E. Halver and K. Tiews (Editors), Finfish Nutrition and Fishfeed Technology. Vol. I. Heeneman, Berlin, pp. 113--125.

Youden, W.J., 1951. Statistical Methods for Chemists. Wiley, New York/London, pp. 24-29.

Yu, T.C. and Sinnhuber, R.O., 1975. Effect of dietary linolenic and linoleic acids upon growth and lipid metabolism of rainbow trout (Salmo gairdneri). Lipids, 10: 63-66.

Yu, T.C. and Sinnhuber, R.O., 1976. Growth response of rainbow trout (S~lmo guirdneri) to dietary w 3 and w6 fatty acids. Aquaeulture, 8: 309-317.

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