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Comparative studies on body composition of rainbow trout (Salmo gairdneri R.) in relation to type of diet and growth rate
Aquaculture, 13 (1978)235-243 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
235
COMPARATIVE STUDIES ON BODY COMPOSITION OF RAINBOW TROUT (SALMO GAIRDNERI R.) IN RELATION TO TYPE OF DIET AND GROWTH RATE
SOFRONIOS E. PAPOUTSOGLOU* Institute
of Oceanographic
and ELLI G. PAPAPARASKEVA-PAPOUTSOGLOU
and Fisheries Research,
Athens
*Present address: Department of Applied Hydrohiology, of Athens (Greece)
(Greece) Agricultural University College
(Received 28 April 1977; revised 20 October 1977)
ABSTRACT Papoutsoglou, S.E. and Papaparaskeva-Papoutoglou, E.G., 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. Three populations of rainbow trout (mean initial live weight 40 g) were fed experimentally under almost the same conditions for 49 weeks. The aim of the experiment was the examination of the changes in the relative proportions of the major whole body constituents (water, protein, fat and ash) in relation to type and amount of diet and growth rate. Two pelleted dry diets (A and B) and one mixed diet (C) were used. The amount of food given daily to the fish in the case of diets A and B was continuously based on fish body weight and water temperature. The population which received diet C (raw material and pelleted dry food) was fed on maximum ratio. Sampling was carried out approximately every two months. After 25 weeks, and besides the regular sampling, fish were sampled from each population and analyses were made on their fillets. The same analyses were also carried out. on fillets and whole body material on a sample of wild fish, of almost the same age, fed on a variety of food organisms in a stream near the experimental tanks. When the results are expressed in terms of dry weight, the analyses of whole body material showed that ash content remained fairly constant in all populations throughout the experimental time. Further, with increasing body weight and age the percentages of water and protein decreased and the percentage of fat content increased in all populations and especially in fish fed on diet C which appeared to have the maximum growth rate and final mean body weight. Similarly, fish fed on diet B, which showed the lowest growth rate and final mean body weight, had low changes in the major body conskituents throughout the experimental period. The lowest and the most regular rate in the changes of these parameters appeared in fish fed on diet A which also had a sufficient growth rate and mean final body weight. Analyses of the fillets for the three different types of food used have different results. The analysed wild fish had the highest percentage of water content and, expressing the results in terms of dry weight, the highest percentage of ash and protein content, while they appeared to have the lowest percentage of fat content, on both whole body material and fillets. Since the three types of diets used in this experiment gave three different growth rates, as well as three different body compositions of the reared trout, it is suggested from the present results that the relative proportions and changes of the four body constituents and effects on the growth rate of trout are strongly affected by the type of food.
236
INTRODUCTION
Owing to their great economic importance and their relatively easy artificial propagation and rearing, rainbow trout are cultivated on a vast scale in many places of the world. One of the most important and basic factors which is closely related to the marketing of this fish is its flesh quantity which is affected by several factors. The type and amount of food are two of the main factors which influence the production of this fish. Therefore, besides its economic relation to trout farmers, food also plays an important role in the nutritive value of trout by influencing their body composition during rearing. Several investigators have studied the salmonid body composition in relation to many factors, i.e. temperature, size, age, diet, stage of development, ration size and body weight (Parker and Vanstone, 1966; Brett et al., 1969; Love, 1970; Lee and Putman, 1973; Elliott, 1976; Denton and Yousef, 1976). The purpose of the investigation reported here was to examine and emphasize the relation between the growth rate and body composition of rainbow trout, when artificially reared and fed on various dry and mixed diets, during the period when fish reach their marketable size. MATERIAL AND METHODS
Three populations (1, 2 and 3) of 500, 27-week-old rainbow trout of mean initial weight 40 g were used. The first two populations were kept in tanks 10 X 1 X 0.8 m at the National Hatchery Station of Edessa. Population 3 was held in an almost identical tank of a fish farmer of the same region. Water supply (290 l/min) and water temperature (13-15°C) and the amount of dissolved oxygen (9-9.5 ppm) was similar in all tanks. Fish of populations 1 and 2 were fed dry pelleted diets (A and B) three times/day. The amounts of given food, throughout the experiment, were adjusted to the fish body weight (3-2%), according to water temperature: Population 3 was fed daily on maximum ration. This diet (C) consisted of plenty of minced poultry wastes in combination with pelleted dry food. The chemical content of all diets used is given in Table I. The experiment lasted 49 weeks (from 1 October 1975 to 10 September 1976). Proximate analyses on 60 specimens of the initial population, for water, protein, fat and ash content, were made at the beginning of the experiment. Random sampling from each tank was carried out approximately every two months and included killing usually 50-60 fish each from populations 1 and 2 and lo-15 fish from population 3, taking the weight and the length of the fish and notes on their external colouration and the amount of accumulated fat along the mesenteries and pyloric caeca. All populations were starved 24 hours before sampling. After killing, the fish of each population were homogenised twice by means of an electrical meat mincer and a sufficient sample of this mixed material was lyophilized by a freeze-drier apparatus. Finally, the lyophilized material
237
TABLE I Chemical composition of used diets (%) Diet
Crude protein
A
48.3
B
40
C Poultry wastes on dry basis
70.4
Pelleted dry ration
56
Crude fat
Carbohydrate
Crude fibre
8.3
18.5
6
6
18
4
13.6
8
4.2
20.5
2.1
3
Ash
9.2 20
Water
9.8 12
8.3
-
12.5
10
was mixed again by means of an electrical blender and was used for the determinations of the major body constituents. The same procedure was also followed, once, on a sample of wild fish (35 specimens of the same age as the farmed fish), taken from a stream near the station. Determination of the fillets composition carried out similarly once, on 10, 10, 5 and 7 specimens from populations 1, 2, 3 and wild fish, respectively, when the fish were 52 weeks old. Moisture determinations were estimated on 10 samples (2 g each) before lyophilization, in a hot-air oven until constant weight was obtained (usually 24 h at 100°C). The dried material was then transferred to a muffle furnace for ash determination (usually 12 h at 500°C). Samples of the lyophilized material were used for the determination of the remaining constituents as follows: crude protein 3 samples (6 sub-samples each) by a micro-kjeldal technique (T.N. X 6.25) and crude fat 7 samples (10 g each), by petroleum ether extraction using a set of soxhlet apparatus. Estimates of protein, fat and ash were expressed as percentages of dry and wet weights of samples while water content was expressed as a percentage of the initial weight of the samples. RESULTS
By the end of the experiment three mean body weight values of trout were obtained representing the nutritional values of the three types of diets used. Thus, the highest growth rate and final mean body weight was given by the population fed on diet C, while trout fed on diet B had the lowest growth rate and final mean body weight. The changes in the different body components for the three studied rainbow trout populations, with mean body weight, mean standard length and age expressed on dry and wet weight bases are presented in Figs 1 and 2.
238
Diet
A
Diet
B
Fig. 1. Changes in body composition of the three investigated rainbow trout populations (Diets A, B, C), with mean body weight, mean standard length and age, expressed on dry weight basis. Diet
A
Diet
B
Diet
C
10
Fig. 2. Changes in body composition of the three investigated rainbow trout popuIations (Diets A, B, C), with mean body weight, mean standard length and age, expressed on wet weight basis.
239
A general tendency of fat increase was observed in all populations with ‘their growth rate and age. This fat increase was remarkably high in the population fed on diet C especially after 25 weeks. Trout fed on diet A showed a very low increase in their fat content with age and growth rate after 25 weeks, while trout fed on diet B showed a slight decrease in their fat content almost from the beginning of the experiment and until the 25th week, after which a rapid increase commenced. Similarly, expressing the results on a dry weight basis, protein percentages decreased with growth rate and age in all populations and especially in trout fed on diets B and C and after the 25th week. Ash content appeared to be almost constant throughout the experiment in trout fed on diets A and B. Fish fed on diet C showed a slight decrease in ash content after the 33rd week of the experiment (Table I). Expressing the results on a wet weight basis, it is apparent that ash content was almost constant in all populations with their growth rate and age. Fat content increased gradually from the beginning to the end of the experiment in trout fed on diets A and C, while in fish fed on diet B a final slight decrease of fat percentage was observed after a gradual initial increase. Similarly, protein percentage, in all populations showed a final decrease after an initial slight increase. All populations showed a gradual decrease in their water content (Table I). The analyses of the edible part of the fish showed that fish fed on diet A had the lowest moisture percentage and the other populations 2 and 3, had values which were almost the same. Also, population 1 appeared to have the highest fat percentage, expressing the results either on a dry or wet weight basis, as well as the lowest ash percentage, although the values of those two components of population 1 were quite close to those of population 3 (Table II). Similarly, the values of protein percentage of populations 1 and 3 were almost the same when the results were expressed on a dry weight basis, while population 1 showed higher protein content than that of population 3, when the results are expressed on a natural basis. Population 2 had the highest protein and ash percentage and the lowest fat percentage, expressing the results on a dry weight basis (Table II). The whole body analyses of the wild fish showed quite a high water percentage and expressing the results on a dry weight basis, a very high protein followed by a relatively low fat percentage as well as a relatively high ash content (Table III). More or less the same situation appeared in the analyses of the fillets on these fish, i.e. high water content, a very high protein and ash content and a relatively very low fat content (Table III). DISCUSSION It is clear from the present results that the three different types of food gave three different growth rates, whole body and fillets composition, as well as final mean body weights. Generally the results of the present study support those obtained by other related works on salmonids and several other fish
II
body
Fish age (wks)
36
44
52
60
68
76
1
2
3
4
5
6
72.57 74.56 71.38
70.69 73.27 71.6
65.57 69.2 67.48
66.7 69.38 64.5
65.73 67 63.28
65.1 66.2 62.63
40 40 15
50 50 10
70 60 15
60 60 15
65 60 15 22.31 22.22 19.2
22.4 22.31 19.53
21.63 20.76 20.55
9.59 7.36 15.28
9.3 7.44 14.78
9.16 6.88 11.89
9.15 6.22 8.29
22.4 22.12 21.46
on wet and dry weight
100.56 99.9 100.2 100.07 100.33 100.56
8.1 9.58 8.8 7.52 10.2 7.1 8.3 9.96 7.34
27.5 22.5 33.5 27.05 22.55 40.27 27.5 21.8 40.9
64.96 67.82 57.9 65.5 67.63 53.19 63.95 67.23 51.38
99.89 99.14 99.85 2.89 3.36 2.74
99.75 98.99 99.62
100.44 100.44 100.36 8.87 8.96 8.84 26.6 20.2 25.52
100.03 100.11 100.2
100.19 99.95 100.06
100.17 100.26 100.11
64.97 71.28 66.0
100.35 100.44 100.83
68.0 70.93 64.13
100.11 100.12 100.14
8.0 9.4 8.46 24.36 20.11 28.24
70.4 63.5
100.73 100.1 100
99.23
Total
bases
8.58 9.5 8.2 22.82 20.2 28.3
16.4
71.43
69.33
(%)
(%)
(%) 11.4
Ash
Fat
Protein
Dry weight
expressed
100.08 100.08 99.98
99.8
Total
rations,
2.6 3.36 2.61
2.7 2.93 3.12
3.05 2.72 2.88
2.35 2.51 2.36
7.14 5.38 7.98
19.93 18.96 18.2
2.82
2.35 2.42 2.34
4.07
(%)
Fat
fed on three different
6.14 5.19 8.09
19.02 17.91 18.17
17.71
(%)
75.2
Protein
(%)
trout,
Water
Wet weight
of rainbow
32 40 10
60
No. of fiih used
composition
No. of sampling
Initial population
Mean whole
TABLE
h3 S
63
Fiih age (WI=)
325
210
303
%I wt (g)
26.1
23.5
25.8
G SL (cm)
5
10
10
No. of fish used
Fillets
Whole body
Material
239
M wt (g)
24.5
M SL (cm)
7
35
No. of fish used
18.99
20.39
22.89
6.16
3.94
7.48
1.52
1.84
1.8
100.03
100.07
100.05
Total
71.28
78.13
71.26
76.83
19.36
16.48 1.92
2.33 1.99
2.52
100.11
100.17
Total
83.55
77.87
Protein (%I
Fat (%)
Water (%I
Protein (%I
Dry weight
Wet weight
78.84
23.13
15.1
23.3
Fat @)
5.7
7.04
5.6
Ash (%a)
8.32
11.0
Fat @1
8.58
11.89
Ash (%I
100.45
100.76
Total
of wild specimens of rainbow trout expressed on wet and dry weight bases
73.36
73.9
67.88
Ash (%I
Protein (%I
Fat (%I
Water (%I
Protein (%I
Dry weight
Wet weight
of rainbow trout, fed on three different rations, expressed on wet and dry weight bases
Mean whole body and mean fillets composition
TABLE IV
C
B
A
Diet
Mean fillets composition
TABLE III
100.11
100.27
100.16
Total
242
(Swift, 1955; Phillips et al., 1966; Brett et al., 1969; Love, 1970; Denton and Yousef, 1976; Ma&s and Erasmus, 1977). So, as the age of the investigated rainbow trout increased the most pronounced change in their body composition was a decrease in water percentage, and an increase in fat percentage. Ash percentage remained almost constant and protein content started with a decrease followed by a slight increase and finally decreased after the 25th week. Similarly, expressing the results on a dry weight basis, protein decreased when fat increased, while ash remained fairly constant. Moreover, the present results, also suggest that the rate of the observed changes in body composition differ between the investigated populations and are positively related to the observed growth rate of the fish. Thus, population 3 had the highest fat and the lowest protein percentage, and the highest growth rate, while the opposite situation was observed in fish fed on diet B. Diet A had the lowest rate in the changes of these parameters and a sufficient growth rate, and final mean body weight. The obtained results could reasonably be explained by taking into consideration the fact that the used diets were different as regards their chemical composition and the amounts used. So, the maximum rations used in’ population 3 with the highest crude protein content in combination with fresh raw material gave the highest mean body weight but also a relatively high body fat content. Population 2, fed on diet B with the lowest protein content, gave the lowest mean body weight and body fat content and finally, the intermediate crude protein content of diet A caused a sufficient final mean body weight and the expected body fat content. The combined data on fillets analyses revealed that diet A caused the highest fat content in fillets, which means that the great majority of the observed fat content in population 3 was present along the mesenteries and pyloric caeca of trout as has previously been demonstrated (Swift, 1955). Comparing these results with those obtained from the analysed wild fish it can be concluded that the free diet of these fish, which was based on various animal organisms, gave an almost complete different body and fillets composition from the farmed fish. The main characteristic of their body composition, namely a very low fat content followed by a high water percentage, is related to starvation of salmonids as has been found by many workers (Wood et al., 1957; Idler and Clemens, 1959). It is clear, therefore, that the type and amount of food influence significantly the body composition, the growth rate and the final mean body weight of farmed trout more than their age does. This means that the nutritional value, or in other words, the quality of the flesh and the final mean body weight of trout, which is closely related to their unit price, or more generally, to the benefit of trout farms, is affected mainly by the type of food. Thus concerning the fact that the great majority of trout farmers, are using dry artificial rations and/or mixed diets in several combinations with raw, : waste or rot materials, it can be emphasized that a proper combination of
243
sufficient body composition and fast growth rate must be the goal of both trout diet makers and trout farmers. ACKNOWLEDGEMENTS
We are grateful to Dr A. Stephanidis for his interest and support and Mr S. Beziridis (Director of the National Hatchery Station of Edessa) and his assistants for their help in rearing the trout. We also wish to thank Dr Druliskos (Nuclear Research Center “Democritos”), and Dr A. Seimenis (State Institute of Veterinary microbiology, department of biological products) for their help in the lyophilization of the samples and Miss A. Leouses for her laboratory assistance.
REFERENCES Brett, J.R., Shelbourne, J.E. and Shoop, C.T., 1969. Growth rate and body composition of fingerling sockeye salmon, Oncorhynchus nerka, in relation to temperature and ration size. J. Fish. Res. Board Can., 26: 2363-2394. Denton, J.E. and Yousef, M.K., 1976. Body composition and organ weights of rainbow trout, Salmo gairdneri. J. Fish Biol., 8: 489-499. Elliott, J.M., 1976. Body composition of brown trout (Salmo trutta L.) in relation to temperature and ration size. J. Anim. Ecol., 45: 273-289. Idler, D.R. and Clemens, W.A., 1959. The energy expenditures of Fraser River sockeye salmon during the spawning migration to Chilko and Stuart Lakes. Int. Pacific Salmon Fish. Comm. Progr. Rep., pp. l-80. Lee, D.J. and Putman, G.B., 1972. The response of Rainbow trout to Varying Protein/ Energy Ratios in a Test diet. J. Nutr., 103: 916-922. Love, R.M., 1970. The Chemical Biology of Fishes, Academic Press, London. Marais, J.F.K. and Erasmus, T., 1977. Body composition of Mugil cephalus, Liza dumerili, Liza richardsoni and Liza kicuspidens (Teleostei: Mugilidae) caught in the Swartkops estuary. Agriculture, 10: 75-86. Parker, R. and Vanstone, W.E., 1966. Changes in chemical composition of Central British Columbia pink salmon during early sea life. J. Fish. Res. Board Can., 23: 1353-1384. Phillips, H.M., Livingstone, D.L. and Poston, H.A., 1966. The effect of changes in protein quality, calorie sources and calorie levels upon the growth and chemical composition of brook trout. N.Y. State Dep. Conserv. Fish. Res., Bull., 29: 6-7. Swift, D.R., 1955. Seasonal variations in the growth rate, thyroid gland activity and food reserves of brown trout (Salmo trutta L.). J. Exp. Biol., 32: 751-764. Wood, E.M., Yasutake, W.T., Woodal, A.N. and Halver, J.E., 1957. The nutrition of salmonoid fishes. II. Studies on production diets. J. Nutr., 61(4): 479-488.
235
COMPARATIVE STUDIES ON BODY COMPOSITION OF RAINBOW TROUT (SALMO GAIRDNERI R.) IN RELATION TO TYPE OF DIET AND GROWTH RATE
SOFRONIOS E. PAPOUTSOGLOU* Institute
of Oceanographic
and ELLI G. PAPAPARASKEVA-PAPOUTSOGLOU
and Fisheries Research,
Athens
*Present address: Department of Applied Hydrohiology, of Athens (Greece)
(Greece) Agricultural University College
(Received 28 April 1977; revised 20 October 1977)
ABSTRACT Papoutsoglou, S.E. and Papaparaskeva-Papoutoglou, E.G., 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. Three populations of rainbow trout (mean initial live weight 40 g) were fed experimentally under almost the same conditions for 49 weeks. The aim of the experiment was the examination of the changes in the relative proportions of the major whole body constituents (water, protein, fat and ash) in relation to type and amount of diet and growth rate. Two pelleted dry diets (A and B) and one mixed diet (C) were used. The amount of food given daily to the fish in the case of diets A and B was continuously based on fish body weight and water temperature. The population which received diet C (raw material and pelleted dry food) was fed on maximum ratio. Sampling was carried out approximately every two months. After 25 weeks, and besides the regular sampling, fish were sampled from each population and analyses were made on their fillets. The same analyses were also carried out. on fillets and whole body material on a sample of wild fish, of almost the same age, fed on a variety of food organisms in a stream near the experimental tanks. When the results are expressed in terms of dry weight, the analyses of whole body material showed that ash content remained fairly constant in all populations throughout the experimental time. Further, with increasing body weight and age the percentages of water and protein decreased and the percentage of fat content increased in all populations and especially in fish fed on diet C which appeared to have the maximum growth rate and final mean body weight. Similarly, fish fed on diet B, which showed the lowest growth rate and final mean body weight, had low changes in the major body conskituents throughout the experimental period. The lowest and the most regular rate in the changes of these parameters appeared in fish fed on diet A which also had a sufficient growth rate and mean final body weight. Analyses of the fillets for the three different types of food used have different results. The analysed wild fish had the highest percentage of water content and, expressing the results in terms of dry weight, the highest percentage of ash and protein content, while they appeared to have the lowest percentage of fat content, on both whole body material and fillets. Since the three types of diets used in this experiment gave three different growth rates, as well as three different body compositions of the reared trout, it is suggested from the present results that the relative proportions and changes of the four body constituents and effects on the growth rate of trout are strongly affected by the type of food.
236
INTRODUCTION
Owing to their great economic importance and their relatively easy artificial propagation and rearing, rainbow trout are cultivated on a vast scale in many places of the world. One of the most important and basic factors which is closely related to the marketing of this fish is its flesh quantity which is affected by several factors. The type and amount of food are two of the main factors which influence the production of this fish. Therefore, besides its economic relation to trout farmers, food also plays an important role in the nutritive value of trout by influencing their body composition during rearing. Several investigators have studied the salmonid body composition in relation to many factors, i.e. temperature, size, age, diet, stage of development, ration size and body weight (Parker and Vanstone, 1966; Brett et al., 1969; Love, 1970; Lee and Putman, 1973; Elliott, 1976; Denton and Yousef, 1976). The purpose of the investigation reported here was to examine and emphasize the relation between the growth rate and body composition of rainbow trout, when artificially reared and fed on various dry and mixed diets, during the period when fish reach their marketable size. MATERIAL AND METHODS
Three populations (1, 2 and 3) of 500, 27-week-old rainbow trout of mean initial weight 40 g were used. The first two populations were kept in tanks 10 X 1 X 0.8 m at the National Hatchery Station of Edessa. Population 3 was held in an almost identical tank of a fish farmer of the same region. Water supply (290 l/min) and water temperature (13-15°C) and the amount of dissolved oxygen (9-9.5 ppm) was similar in all tanks. Fish of populations 1 and 2 were fed dry pelleted diets (A and B) three times/day. The amounts of given food, throughout the experiment, were adjusted to the fish body weight (3-2%), according to water temperature: Population 3 was fed daily on maximum ration. This diet (C) consisted of plenty of minced poultry wastes in combination with pelleted dry food. The chemical content of all diets used is given in Table I. The experiment lasted 49 weeks (from 1 October 1975 to 10 September 1976). Proximate analyses on 60 specimens of the initial population, for water, protein, fat and ash content, were made at the beginning of the experiment. Random sampling from each tank was carried out approximately every two months and included killing usually 50-60 fish each from populations 1 and 2 and lo-15 fish from population 3, taking the weight and the length of the fish and notes on their external colouration and the amount of accumulated fat along the mesenteries and pyloric caeca. All populations were starved 24 hours before sampling. After killing, the fish of each population were homogenised twice by means of an electrical meat mincer and a sufficient sample of this mixed material was lyophilized by a freeze-drier apparatus. Finally, the lyophilized material
237
TABLE I Chemical composition of used diets (%) Diet
Crude protein
A
48.3
B
40
C Poultry wastes on dry basis
70.4
Pelleted dry ration
56
Crude fat
Carbohydrate
Crude fibre
8.3
18.5
6
6
18
4
13.6
8
4.2
20.5
2.1
3
Ash
9.2 20
Water
9.8 12
8.3
-
12.5
10
was mixed again by means of an electrical blender and was used for the determinations of the major body constituents. The same procedure was also followed, once, on a sample of wild fish (35 specimens of the same age as the farmed fish), taken from a stream near the station. Determination of the fillets composition carried out similarly once, on 10, 10, 5 and 7 specimens from populations 1, 2, 3 and wild fish, respectively, when the fish were 52 weeks old. Moisture determinations were estimated on 10 samples (2 g each) before lyophilization, in a hot-air oven until constant weight was obtained (usually 24 h at 100°C). The dried material was then transferred to a muffle furnace for ash determination (usually 12 h at 500°C). Samples of the lyophilized material were used for the determination of the remaining constituents as follows: crude protein 3 samples (6 sub-samples each) by a micro-kjeldal technique (T.N. X 6.25) and crude fat 7 samples (10 g each), by petroleum ether extraction using a set of soxhlet apparatus. Estimates of protein, fat and ash were expressed as percentages of dry and wet weights of samples while water content was expressed as a percentage of the initial weight of the samples. RESULTS
By the end of the experiment three mean body weight values of trout were obtained representing the nutritional values of the three types of diets used. Thus, the highest growth rate and final mean body weight was given by the population fed on diet C, while trout fed on diet B had the lowest growth rate and final mean body weight. The changes in the different body components for the three studied rainbow trout populations, with mean body weight, mean standard length and age expressed on dry and wet weight bases are presented in Figs 1 and 2.
238
Diet
A
Diet
B
Fig. 1. Changes in body composition of the three investigated rainbow trout populations (Diets A, B, C), with mean body weight, mean standard length and age, expressed on dry weight basis. Diet
A
Diet
B
Diet
C
10
Fig. 2. Changes in body composition of the three investigated rainbow trout popuIations (Diets A, B, C), with mean body weight, mean standard length and age, expressed on wet weight basis.
239
A general tendency of fat increase was observed in all populations with ‘their growth rate and age. This fat increase was remarkably high in the population fed on diet C especially after 25 weeks. Trout fed on diet A showed a very low increase in their fat content with age and growth rate after 25 weeks, while trout fed on diet B showed a slight decrease in their fat content almost from the beginning of the experiment and until the 25th week, after which a rapid increase commenced. Similarly, expressing the results on a dry weight basis, protein percentages decreased with growth rate and age in all populations and especially in trout fed on diets B and C and after the 25th week. Ash content appeared to be almost constant throughout the experiment in trout fed on diets A and B. Fish fed on diet C showed a slight decrease in ash content after the 33rd week of the experiment (Table I). Expressing the results on a wet weight basis, it is apparent that ash content was almost constant in all populations with their growth rate and age. Fat content increased gradually from the beginning to the end of the experiment in trout fed on diets A and C, while in fish fed on diet B a final slight decrease of fat percentage was observed after a gradual initial increase. Similarly, protein percentage, in all populations showed a final decrease after an initial slight increase. All populations showed a gradual decrease in their water content (Table I). The analyses of the edible part of the fish showed that fish fed on diet A had the lowest moisture percentage and the other populations 2 and 3, had values which were almost the same. Also, population 1 appeared to have the highest fat percentage, expressing the results either on a dry or wet weight basis, as well as the lowest ash percentage, although the values of those two components of population 1 were quite close to those of population 3 (Table II). Similarly, the values of protein percentage of populations 1 and 3 were almost the same when the results were expressed on a dry weight basis, while population 1 showed higher protein content than that of population 3, when the results are expressed on a natural basis. Population 2 had the highest protein and ash percentage and the lowest fat percentage, expressing the results on a dry weight basis (Table II). The whole body analyses of the wild fish showed quite a high water percentage and expressing the results on a dry weight basis, a very high protein followed by a relatively low fat percentage as well as a relatively high ash content (Table III). More or less the same situation appeared in the analyses of the fillets on these fish, i.e. high water content, a very high protein and ash content and a relatively very low fat content (Table III). DISCUSSION It is clear from the present results that the three different types of food gave three different growth rates, whole body and fillets composition, as well as final mean body weights. Generally the results of the present study support those obtained by other related works on salmonids and several other fish
II
body
Fish age (wks)
36
44
52
60
68
76
1
2
3
4
5
6
72.57 74.56 71.38
70.69 73.27 71.6
65.57 69.2 67.48
66.7 69.38 64.5
65.73 67 63.28
65.1 66.2 62.63
40 40 15
50 50 10
70 60 15
60 60 15
65 60 15 22.31 22.22 19.2
22.4 22.31 19.53
21.63 20.76 20.55
9.59 7.36 15.28
9.3 7.44 14.78
9.16 6.88 11.89
9.15 6.22 8.29
22.4 22.12 21.46
on wet and dry weight
100.56 99.9 100.2 100.07 100.33 100.56
8.1 9.58 8.8 7.52 10.2 7.1 8.3 9.96 7.34
27.5 22.5 33.5 27.05 22.55 40.27 27.5 21.8 40.9
64.96 67.82 57.9 65.5 67.63 53.19 63.95 67.23 51.38
99.89 99.14 99.85 2.89 3.36 2.74
99.75 98.99 99.62
100.44 100.44 100.36 8.87 8.96 8.84 26.6 20.2 25.52
100.03 100.11 100.2
100.19 99.95 100.06
100.17 100.26 100.11
64.97 71.28 66.0
100.35 100.44 100.83
68.0 70.93 64.13
100.11 100.12 100.14
8.0 9.4 8.46 24.36 20.11 28.24
70.4 63.5
100.73 100.1 100
99.23
Total
bases
8.58 9.5 8.2 22.82 20.2 28.3
16.4
71.43
69.33
(%)
(%)
(%) 11.4
Ash
Fat
Protein
Dry weight
expressed
100.08 100.08 99.98
99.8
Total
rations,
2.6 3.36 2.61
2.7 2.93 3.12
3.05 2.72 2.88
2.35 2.51 2.36
7.14 5.38 7.98
19.93 18.96 18.2
2.82
2.35 2.42 2.34
4.07
(%)
Fat
fed on three different
6.14 5.19 8.09
19.02 17.91 18.17
17.71
(%)
75.2
Protein
(%)
trout,
Water
Wet weight
of rainbow
32 40 10
60
No. of fiih used
composition
No. of sampling
Initial population
Mean whole
TABLE
h3 S
63
Fiih age (WI=)
325
210
303
%I wt (g)
26.1
23.5
25.8
G SL (cm)
5
10
10
No. of fish used
Fillets
Whole body
Material
239
M wt (g)
24.5
M SL (cm)
7
35
No. of fish used
18.99
20.39
22.89
6.16
3.94
7.48
1.52
1.84
1.8
100.03
100.07
100.05
Total
71.28
78.13
71.26
76.83
19.36
16.48 1.92
2.33 1.99
2.52
100.11
100.17
Total
83.55
77.87
Protein (%I
Fat (%)
Water (%I
Protein (%I
Dry weight
Wet weight
78.84
23.13
15.1
23.3
Fat @)
5.7
7.04
5.6
Ash (%a)
8.32
11.0
Fat @1
8.58
11.89
Ash (%I
100.45
100.76
Total
of wild specimens of rainbow trout expressed on wet and dry weight bases
73.36
73.9
67.88
Ash (%I
Protein (%I
Fat (%I
Water (%I
Protein (%I
Dry weight
Wet weight
of rainbow trout, fed on three different rations, expressed on wet and dry weight bases
Mean whole body and mean fillets composition
TABLE IV
C
B
A
Diet
Mean fillets composition
TABLE III
100.11
100.27
100.16
Total
242
(Swift, 1955; Phillips et al., 1966; Brett et al., 1969; Love, 1970; Denton and Yousef, 1976; Ma&s and Erasmus, 1977). So, as the age of the investigated rainbow trout increased the most pronounced change in their body composition was a decrease in water percentage, and an increase in fat percentage. Ash percentage remained almost constant and protein content started with a decrease followed by a slight increase and finally decreased after the 25th week. Similarly, expressing the results on a dry weight basis, protein decreased when fat increased, while ash remained fairly constant. Moreover, the present results, also suggest that the rate of the observed changes in body composition differ between the investigated populations and are positively related to the observed growth rate of the fish. Thus, population 3 had the highest fat and the lowest protein percentage, and the highest growth rate, while the opposite situation was observed in fish fed on diet B. Diet A had the lowest rate in the changes of these parameters and a sufficient growth rate, and final mean body weight. The obtained results could reasonably be explained by taking into consideration the fact that the used diets were different as regards their chemical composition and the amounts used. So, the maximum rations used in’ population 3 with the highest crude protein content in combination with fresh raw material gave the highest mean body weight but also a relatively high body fat content. Population 2, fed on diet B with the lowest protein content, gave the lowest mean body weight and body fat content and finally, the intermediate crude protein content of diet A caused a sufficient final mean body weight and the expected body fat content. The combined data on fillets analyses revealed that diet A caused the highest fat content in fillets, which means that the great majority of the observed fat content in population 3 was present along the mesenteries and pyloric caeca of trout as has previously been demonstrated (Swift, 1955). Comparing these results with those obtained from the analysed wild fish it can be concluded that the free diet of these fish, which was based on various animal organisms, gave an almost complete different body and fillets composition from the farmed fish. The main characteristic of their body composition, namely a very low fat content followed by a high water percentage, is related to starvation of salmonids as has been found by many workers (Wood et al., 1957; Idler and Clemens, 1959). It is clear, therefore, that the type and amount of food influence significantly the body composition, the growth rate and the final mean body weight of farmed trout more than their age does. This means that the nutritional value, or in other words, the quality of the flesh and the final mean body weight of trout, which is closely related to their unit price, or more generally, to the benefit of trout farms, is affected mainly by the type of food. Thus concerning the fact that the great majority of trout farmers, are using dry artificial rations and/or mixed diets in several combinations with raw, : waste or rot materials, it can be emphasized that a proper combination of
243
sufficient body composition and fast growth rate must be the goal of both trout diet makers and trout farmers. ACKNOWLEDGEMENTS
We are grateful to Dr A. Stephanidis for his interest and support and Mr S. Beziridis (Director of the National Hatchery Station of Edessa) and his assistants for their help in rearing the trout. We also wish to thank Dr Druliskos (Nuclear Research Center “Democritos”), and Dr A. Seimenis (State Institute of Veterinary microbiology, department of biological products) for their help in the lyophilization of the samples and Miss A. Leouses for her laboratory assistance.
REFERENCES Brett, J.R., Shelbourne, J.E. and Shoop, C.T., 1969. Growth rate and body composition of fingerling sockeye salmon, Oncorhynchus nerka, in relation to temperature and ration size. J. Fish. Res. Board Can., 26: 2363-2394. Denton, J.E. and Yousef, M.K., 1976. Body composition and organ weights of rainbow trout, Salmo gairdneri. J. Fish Biol., 8: 489-499. Elliott, J.M., 1976. Body composition of brown trout (Salmo trutta L.) in relation to temperature and ration size. J. Anim. Ecol., 45: 273-289. Idler, D.R. and Clemens, W.A., 1959. The energy expenditures of Fraser River sockeye salmon during the spawning migration to Chilko and Stuart Lakes. Int. Pacific Salmon Fish. Comm. Progr. Rep., pp. l-80. Lee, D.J. and Putman, G.B., 1972. The response of Rainbow trout to Varying Protein/ Energy Ratios in a Test diet. J. Nutr., 103: 916-922. Love, R.M., 1970. The Chemical Biology of Fishes, Academic Press, London. Marais, J.F.K. and Erasmus, T., 1977. Body composition of Mugil cephalus, Liza dumerili, Liza richardsoni and Liza kicuspidens (Teleostei: Mugilidae) caught in the Swartkops estuary. Agriculture, 10: 75-86. Parker, R. and Vanstone, W.E., 1966. Changes in chemical composition of Central British Columbia pink salmon during early sea life. J. Fish. Res. Board Can., 23: 1353-1384. Phillips, H.M., Livingstone, D.L. and Poston, H.A., 1966. The effect of changes in protein quality, calorie sources and calorie levels upon the growth and chemical composition of brook trout. N.Y. State Dep. Conserv. Fish. Res., Bull., 29: 6-7. Swift, D.R., 1955. Seasonal variations in the growth rate, thyroid gland activity and food reserves of brown trout (Salmo trutta L.). J. Exp. Biol., 32: 751-764. Wood, E.M., Yasutake, W.T., Woodal, A.N. and Halver, J.E., 1957. The nutrition of salmonoid fishes. II. Studies on production diets. J. Nutr., 61(4): 479-488.