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A preliminary study on the protein requirements of Chanos chanos (Forskal) fry in a controlled environment
Aquaculture, 17 (1979) 195-201 o Elsevier Scientific Publishing Company,
A PRELIMINARY CHANOS
CHANOS
195 Amsterdam
- Printed
in The Netherlands
STUDY ON THE PROTEIN REQUIREMENTS OF (FORSKAL) FRY IN A CONTROLLED ENVIRON-
MENT*
CHHORN
LIM, SOMCHART
Aquaculture Department, Zloilo City (Philippines) *Contribution (Accepted
SUKHAWONGS
and FELICITAS
Southeast Asian Fisheries Development
P. PASCUAL Cenfer, P.O. Box 256,
No. 33. 1 March 1979)
ABSTRACT Lim, C., Sukhawongs, S. and Pascual, F.P., 1979. A preliminary study on the protein requirements of Chanos chanos (Forskal) fry in a controlled environment. Aquaculture, 17: 195-201. Milkfish (Chanos chanos) fry with an average weight of 40 mg per fish were stocked in 60-I wooden--glass aquaria filled with 30 I of filtered sea water with a salinity of 32-34 p.p.t. and a temperature of 25-28°C. They were fed diets containing 20, 30, 40, 50 and 60% protein and 2740 kcal of digestible energy per kg at a daily rate of 10% of the biomass for a period of 30 days. Fish which were fed the diet containing 40% protein had the high est weight gain which was significantly higher (P < 0.05) than those of fish receiving the lower dietary levels of protein. Slightly lower weight gains were obtained when fish were fed diets containing 50 and 60% protein. Although feed conversion values were not statistically different (P < 0.05) among all treatments, the value for the 40% protein diet (1.96 was the best. The mean survival rates were low for all treatments but was highest for the 40% protein diet. No significant difference (P < 0.05) was found in the survival rates of fish receiving different treatments. Results show that a dietary level of 40% protein was required by milkfish fry for maximum growth, efficient feed conversion and high survival rate.
INTRODUCTION
The milkfish Chanos chanos (Forskal) is an important food fish cultured for centuries in the Philippines, Indonesia and Taiwan. However, milkfish farming is still traditional, and the yield is limited by the natural carrying capacity of the body of water. The primary concern in fish culture is to increase fish production per unit of culture space. Supplementary feeding with artificial diets is an effective measure to increase fish production. However, to render the production economical, supplemental diets must be formulated in accordance with the basic nutritional requirements of the particular species. In fact, there is a dearth of
196
studies regarding nutritional requirements for the milkfish. Lee and Liao (1976) tested various sources of protein with milkfish fingerlings with an average weight of 1.7 g, in aquaria at 25 to 28°C water temperature and 24-30 p.p.t. salinity. They found that a test diet using vitamin-free casein supplemented with L-tryptophan was best for growth. Being the principal diet component for growth, protein has been given priority in nutritional requirement studies. Its quality and quantity markedly affect the growth response of fishes. Its high cost also affects the economics of fish farming. Generally, fish have been known to require higher dietary protein than homoiothermic animals. Except for the study of Lee and Liao (1976), most of the data on protein requirement of fish are for species cultured in an environment different from that of the milkfish. Thus, this experiment was designed to determine the optimum dietary level of protein necessary for satisfactory growth and survival for milkfish Chanos chanos reared in a controlled environment. MATERIALS
AND METHODS
Facilities and experimental fish Ten 60-I rectangular wooden-glass aquaria were used in this feeding study. Each aquarium had an individual air supply and was filled with approximately 30 1 of sea water. Sea water from the bay of Tigbauan filtered through a sandgravel filter was used in this study. The water temperature range was 25 to 28°C and the salinity was 32 to 34 p.p.t. Wild milkfish fry with an average weight of 40 mg were obtained from a fry concessionaire. They were acclimatized to laboratory conditions for 1 week prior to the start of the experiment. During this period they received the same diet containing 30% protein at a rate of 15% biomass per day. They were randomly selected and stocked at a density of 40 fish per aquarium. Experimental
diets
Five semi-purified diets were prepared to contain 20,30,40, 50 and 60% protein. They were isocaloric and contained approximately 2740 kcaI of digestible energy (D.E.) per kg. The diets were formulated to contain all essential nutrients necessary for growth in the same quantity, except for the level of protein (Table I). The dry ingredients of each diet were mixed in a Hobart mixer for about IO min. The oils were gradually added to the mixture and the ingredients were mixed for another 5 min. Subsequently, a sufficient quantity of water was added to the dry mixture, blended for a further 5 min and extruded through a 2-mm diameter die in a Hobart meat grinder. The extruded moist pellets were oven-dried at 60°C to stabilize moisture content at approximately 10%. The pellets were pulverized with a kitchen blender and sieved through No. 60 mesh sieve, stored in plastic bags and kept refrigerated at 4°C during the experimental period.
197 TABLE
I
Composition Ingredients
of five isocaloric
experimental
diets containing
Percentages
of ingredients
1
2
Casein 22 Dextrin 60.4 Cod liver oil 3 Corn oil 3 C.M.C. 3 Vitamin mix* 3 Mineral mix* * 5.6 B.H.T. 0.02 Celite 0 Estimated protein (a) 20 Determined protein (%) 24.0 Estimated D.E. (kcal/kg)*** 2,740
various
levels of protein
in diets 3
4
5
33 45.8 3 3 3 3 5.6 0.02 3.6 30
44 31.2’ 3 3 3 3 5.6 0.02 7.4 40
55 16.8 3 3 3 3 5.6 0.02 10.6 50
66 1.5 3 3 3 3 5.6 0.02 14.9 60
31.0
39.1
48.2
56.9
2,740
2,740
2,740
2,740
*Vitamin mix (mg/kg diet): thiamine, 10; riboflavin, 20; pyridoxine, 15; folic acid, 5; pantothenic acid, 40; choline chloride, 3000; niacin, 150; vitamin B,,, 0.02; vitamin A, 4; vitamin D, 10; Vitamin E, 50; menadione-Na-bisulfite, 80; inositol, 400; biotin, 2; vitamin C, 300; B.H.T., 0.50; celite, 25,913.48. **Mineral mix (g/kg diet): CaHP0,.2H,O, 20.7; CaCO,, 14.8; KH,PO,, 10.0; KCl, 1.0; NaCl, 6.0;MnSO,.H,O, 0.35;FeS0,.7Hz0,0.5;MgS0,, 3.0;KIO,,0.01;CuS0,.5H,O, 0.03; ZnCO,, 0.15; CoCl,, 0.0027; NaMo0,.2H,O, 0.0083; Na,SeO,, 0.0002. ***Estimated D.E. was based on the value for channel catfish (Wilson, 1977); protein: 3.5 kcal/g; fat: 8.1 kcal/g; NFE: 2.5 kcal/g.
Treatments This experiment consisted of five treatments with two replications per treatment. The treatments were assigned randomly using a completely randomized design. The fish in two aquaria were given each of the experimental diets containing various levels of protein. Management Milkfish fry were fed twice daily (half of the ration at 9.00 a.m. and half at 5.00 p.m.), 7 days per week at a rate of 10% (dry matter) of their body weight per day. Fish were weighed and counted every 10 days to record weight gain and survival rate. Feed allowances were changed every 10 days. Calculations of total feed allowances were initially based on the average weight of fish in all treatments. Thereafter, they were adjusted, based on the average weight of fish in each treatment and the number of fish in each aquarium.
198
The water in all aquaria was changed twice daily at 8.00 a.m. and at 4.00 p.m. before the fish were fed. Only one-half of the water was changed each time. All aquaria were cleaned thoroughly every morning before the removal of water. The volume of water in each aquarium was adjusted to the number of fish present. Water temperature and salinity were measured twice daily, morning and afternoon, after the water had been changed, and before the fish were fed. The fish were given the experimental diets for a period of 30 days. RESULTS
The growth curves of milkfish fry fed on the experimental diets containing various levels of protein for a period of 30 days are presented in Fig. 1. The
,200
t
Protan
01
0
I
10 Time (days
ievel5
I
I
20
30
1
Fig. 1. Growth curve for milkfish fry fed diets containing various levels of protein.
progressive increase in growth rate of fish appeared to be directly related to the levels of the protein in the diets up to 40%, above which a decline in growth was observed. Fish fed the diets containing 50 and 60% protein grew slower than those fed the 40% protein diet. Milkfish fry which were fed the 40% protein diet had the highest average weight gain (134.7 mg). This weight gain was significantly higher (P < 0.05) than those fed 20 and 30% protein diets, which had weight gains of 43.3 and 65.5 mg, respectively (Table II and Fig. 2). Fish which were fed the two highest levels, 50 and 60% protein, showed lower weight gains (112.3 and 110.0 mg) compared to those receiving the diet containing 40% protein. Feed efficiency expressed in feed conversion values is a reflection of the
199 TABLE II Weight gains, diet conversions and survival rates for milkfish (Chanos chanos) fry fed various dietary levels of protein* Dietary levels of protein (%)
wt gain per fish (mg)
Diet conversion
Survival rate (%)
20 30 40 50 60
43.3= 65.5= 134.7b 112.3b llO.Ob
2.46a 2.20a 1.96a 1.9ga 2.02a
7.5= 12.5a 30.0a 27.5a 28.8a
*Treatment
means with the same superscript are not statistically different at P < 0.05.
140
134.7
120
110.0 112.3
100 % E ; 60 .^ 1 .v' L $
656
60-
30
Protein
40
60
60
levels in diet (%)
Fig. 2. Relationship between weight gains of milkfish fry and the dietary levels of protein.
weight gain (Table II). The best feed conversion of 1.96 was obtained for the 40% protein diet. However, no statistical difference (P < 0.05) was found among fish which were fed various dietary levels of protein. Nevertheless, those diets with lower of higher than 40% protein tended to be less efficient. There was no incidence of high mortality during this 30-day feeding experiment. The mean survival rates were generally low but was highest (30%) for the group that received the 40% protein diet (Table II). No statistical differences (P < 0.05) were found among treatment means. However, a similar trend to that of weight gain could be discerned. Those fed the 50 and 60% protein diets had survival rates slightly lower than those fed the 40% protein diet, whereas those fed the lower protein levels (20 and 30%) showed the lowest survival rates (27.5 and 28.8% vs 7.5 and 12.5%, respectively).
200
DISCUSSION
The mean weight gains of milkfish fry were directly related to the levels of protein in the diet up to 40%. Fish fed the 40% protein diet had the highest weight gain. Thus, a dietary level of protein of 40% seemed to be optimum for milkfish fry fed at a daily rate of 10% biomass. Similar results were obtained by Dupree and Sneed (1966) with channel catfish (Ictalurus punctatus). They found weight gains of channel catfish fingerlings which were fed diets containing different percentages of casein, gluten or soybean were linear with protein content in diets up to 40% protein. However, Deyoe et al. (1968) reported that 25% was the minimum level of protein for maximum growth of channel catfish fingerlings. Simco and Cross (1966) suggested that a practical diet with 30% protein was the most economical for channel catfish raised in earthen ponds. Love11 (1969) indicated that the optimum level of protein for growth of channel catfish ranged from 25 to 40% of the dry ration. Delong et al. (1958) reported that the protein requirements for chinook salmon fed purified diets in tanks at 8 and 14°C were 40 and 55%, respectively. Halver (1976) generalized that the apparent protein requirements were essentially the same for trout and salmon when raised at the same water temperature and was about 50% for fry, with a reduction in requirement as fish increased in size. He also reported that the protein requirement of salmonids increased with increasing salinity and that the protein requirement of trout increased from 40% at 10 p.p.t. salinity to 45% at 20 p.p.t. The protein requirement for optimum growth of Cyprinus carpio fingerling was determined to be around 40% (Ogino and Saito, 1970). With grass carp (Ctenopharyngodon idellus) fry raised in a controlled environment, Dabrowski (1977) observed maximum weight gain when the dietary level of protein was 43%. Cowey et al. (1972) found that the optimum dietary level of protein requirement for plaice Pleuronectes plutessu, was approximately 50%. The slightly lower weight gains of fish fed the diets containing 50 and 60% protein compared to those fed the 40% protein diet could be due to insufficient non-protein energy in the diets. Prather and Love11(1973) indicated that diets with high levels of protein and low amount of non-protein energy may be toxic to channel catfish. The relatively high mortality in this study may be due to environmental stresses such as high salinity (32-34 p.p.t.) and low water temperature (2528°C) which might have caused the gradual death of milkfish fry. However, the fact that the level of 40% protein supported highest survival rate compared to other protein levels suggests that 40% protein was also adequate to maintain satisfactory resistance of the milkfish fry against environmental stresses. CONCLUSION
Comparison of the protein requirements of warm-water fishes indicated that they vary for different species. Within the same species they vary with the size
201
of fish, water temperature and salinity, stocking density, feeding rate, amount of non-protein energy in the feed, quality of the protein or culture procedures. In the present study, results showed that 40% protein is the optimum dietary level required for maximum growth of milkfish, Chanos chanos fry fed 10% biomass per day in a controlled environment. This quantity was also necessary to maintain fish against environmental stresses. Increasing the dietary levels of protein beyond 40% slightly reduced the growth rate. This could be due to the toxic effect of high protein content in the diets with insufficient non-protein energy as has been reported in channel catfish by Prather and Love11 (1973). ACKNOWLEDGEMENT
This study was supported partially through a grant to the Aquaculture Department by the International Development Research Centre of Canada under Project No. 3 p. 74-0146.
REFERENCES Cowey, C.B., Pope, J.A., Adron, J.W. and Blair, A., 1972. Studies on the nutrition of marine flat fish. The protein requirement of plaice Pleuronectes platessa. Br. J. Nutr., 28: 447456. Dabrowski, K., 1977. Protein requirement of grass carp (Ctenopharyngodon idella Val.). Aquaculture, 12 (1): 63-73. Delong, D.C., Halver, J.E. and Mertz, E.T., 1958. Nutrition of salmonid fish - VI. Protein requirements of chinook salmon at two water temperatures. J. Nutr., 65: 589-599. Deyoe, C.W., Teimeier, O.W. and Suppres, C., 1968. Effects of protein, amino acid levels and feeding methods on growth of fingerling channel catfish. Prog. Fish Cult., 30(4): 187195. Dupree, H.K. and Sneed, K.E., 1966. Responses of channel catfish fingerling to different levels of major nutrients in purified diets. U.S. Dept of the Interior. Bur. Spt. Fish. Wildlf. Tech. Pap. No. 9, 21 pp. Halver, J.E., 1976. Formulating practical diets for fish, J. Fish. Res. Board Can., 33: 10321039. Lee, D.L. and Liao, I.C., 1976. A preliminary study on the purified test diet for young milkfish Cfianos chanos. Proc. Int. Milkfish Workshop Conf. 19-22 May 1976, Tigbauan, Iloilo, Philippines, pp. 104-120. Lovell, R.T., 1969. Nutrition in commercial catfish culture. Presented at the 99th Meeting of the Am. Fish. Sot., 26 Sept. 1969, New Orleans, Louisiana, 33 pp. Ogino, C. and Saito, K., 1970, Protein nutrition in fish - I. The utilization of dietary protein by young carp. Jpn. Sot. Sci. Fish., 36: 250-254. Prather, E.E. and Lovell, R.T., 1973. Response of intensively fed channel catfish to diets containing various proteinenergy ratios. Dept of Fisheries and Allied Aquacultures. Auburn Agric. Exp. Stn. Auburn, Alabama, 11 pp. Simco, B.A. and Cross, F.B., 1966. Factors influencing growth and production of channel catfish, Zctaluruspunctatus. Univ. Kans. Publ., Mus. Nat. Hist., 17(4): 191-256. Wilson, R.P., 1977. Energy relationships in catfish diets. In: R.R. Stickney and R.T. Love11 (Editors), Nutrition and Feeding of Channel Catfish. Southern Cooperative Series Bull. 218. Auburn Agric. Exp. Stn, Auburn, Alabama, pp. 21-29.
A PRELIMINARY CHANOS
CHANOS
195 Amsterdam
- Printed
in The Netherlands
STUDY ON THE PROTEIN REQUIREMENTS OF (FORSKAL) FRY IN A CONTROLLED ENVIRON-
MENT*
CHHORN
LIM, SOMCHART
Aquaculture Department, Zloilo City (Philippines) *Contribution (Accepted
SUKHAWONGS
and FELICITAS
Southeast Asian Fisheries Development
P. PASCUAL Cenfer, P.O. Box 256,
No. 33. 1 March 1979)
ABSTRACT Lim, C., Sukhawongs, S. and Pascual, F.P., 1979. A preliminary study on the protein requirements of Chanos chanos (Forskal) fry in a controlled environment. Aquaculture, 17: 195-201. Milkfish (Chanos chanos) fry with an average weight of 40 mg per fish were stocked in 60-I wooden--glass aquaria filled with 30 I of filtered sea water with a salinity of 32-34 p.p.t. and a temperature of 25-28°C. They were fed diets containing 20, 30, 40, 50 and 60% protein and 2740 kcal of digestible energy per kg at a daily rate of 10% of the biomass for a period of 30 days. Fish which were fed the diet containing 40% protein had the high est weight gain which was significantly higher (P < 0.05) than those of fish receiving the lower dietary levels of protein. Slightly lower weight gains were obtained when fish were fed diets containing 50 and 60% protein. Although feed conversion values were not statistically different (P < 0.05) among all treatments, the value for the 40% protein diet (1.96 was the best. The mean survival rates were low for all treatments but was highest for the 40% protein diet. No significant difference (P < 0.05) was found in the survival rates of fish receiving different treatments. Results show that a dietary level of 40% protein was required by milkfish fry for maximum growth, efficient feed conversion and high survival rate.
INTRODUCTION
The milkfish Chanos chanos (Forskal) is an important food fish cultured for centuries in the Philippines, Indonesia and Taiwan. However, milkfish farming is still traditional, and the yield is limited by the natural carrying capacity of the body of water. The primary concern in fish culture is to increase fish production per unit of culture space. Supplementary feeding with artificial diets is an effective measure to increase fish production. However, to render the production economical, supplemental diets must be formulated in accordance with the basic nutritional requirements of the particular species. In fact, there is a dearth of
196
studies regarding nutritional requirements for the milkfish. Lee and Liao (1976) tested various sources of protein with milkfish fingerlings with an average weight of 1.7 g, in aquaria at 25 to 28°C water temperature and 24-30 p.p.t. salinity. They found that a test diet using vitamin-free casein supplemented with L-tryptophan was best for growth. Being the principal diet component for growth, protein has been given priority in nutritional requirement studies. Its quality and quantity markedly affect the growth response of fishes. Its high cost also affects the economics of fish farming. Generally, fish have been known to require higher dietary protein than homoiothermic animals. Except for the study of Lee and Liao (1976), most of the data on protein requirement of fish are for species cultured in an environment different from that of the milkfish. Thus, this experiment was designed to determine the optimum dietary level of protein necessary for satisfactory growth and survival for milkfish Chanos chanos reared in a controlled environment. MATERIALS
AND METHODS
Facilities and experimental fish Ten 60-I rectangular wooden-glass aquaria were used in this feeding study. Each aquarium had an individual air supply and was filled with approximately 30 1 of sea water. Sea water from the bay of Tigbauan filtered through a sandgravel filter was used in this study. The water temperature range was 25 to 28°C and the salinity was 32 to 34 p.p.t. Wild milkfish fry with an average weight of 40 mg were obtained from a fry concessionaire. They were acclimatized to laboratory conditions for 1 week prior to the start of the experiment. During this period they received the same diet containing 30% protein at a rate of 15% biomass per day. They were randomly selected and stocked at a density of 40 fish per aquarium. Experimental
diets
Five semi-purified diets were prepared to contain 20,30,40, 50 and 60% protein. They were isocaloric and contained approximately 2740 kcaI of digestible energy (D.E.) per kg. The diets were formulated to contain all essential nutrients necessary for growth in the same quantity, except for the level of protein (Table I). The dry ingredients of each diet were mixed in a Hobart mixer for about IO min. The oils were gradually added to the mixture and the ingredients were mixed for another 5 min. Subsequently, a sufficient quantity of water was added to the dry mixture, blended for a further 5 min and extruded through a 2-mm diameter die in a Hobart meat grinder. The extruded moist pellets were oven-dried at 60°C to stabilize moisture content at approximately 10%. The pellets were pulverized with a kitchen blender and sieved through No. 60 mesh sieve, stored in plastic bags and kept refrigerated at 4°C during the experimental period.
197 TABLE
I
Composition Ingredients
of five isocaloric
experimental
diets containing
Percentages
of ingredients
1
2
Casein 22 Dextrin 60.4 Cod liver oil 3 Corn oil 3 C.M.C. 3 Vitamin mix* 3 Mineral mix* * 5.6 B.H.T. 0.02 Celite 0 Estimated protein (a) 20 Determined protein (%) 24.0 Estimated D.E. (kcal/kg)*** 2,740
various
levels of protein
in diets 3
4
5
33 45.8 3 3 3 3 5.6 0.02 3.6 30
44 31.2’ 3 3 3 3 5.6 0.02 7.4 40
55 16.8 3 3 3 3 5.6 0.02 10.6 50
66 1.5 3 3 3 3 5.6 0.02 14.9 60
31.0
39.1
48.2
56.9
2,740
2,740
2,740
2,740
*Vitamin mix (mg/kg diet): thiamine, 10; riboflavin, 20; pyridoxine, 15; folic acid, 5; pantothenic acid, 40; choline chloride, 3000; niacin, 150; vitamin B,,, 0.02; vitamin A, 4; vitamin D, 10; Vitamin E, 50; menadione-Na-bisulfite, 80; inositol, 400; biotin, 2; vitamin C, 300; B.H.T., 0.50; celite, 25,913.48. **Mineral mix (g/kg diet): CaHP0,.2H,O, 20.7; CaCO,, 14.8; KH,PO,, 10.0; KCl, 1.0; NaCl, 6.0;MnSO,.H,O, 0.35;FeS0,.7Hz0,0.5;MgS0,, 3.0;KIO,,0.01;CuS0,.5H,O, 0.03; ZnCO,, 0.15; CoCl,, 0.0027; NaMo0,.2H,O, 0.0083; Na,SeO,, 0.0002. ***Estimated D.E. was based on the value for channel catfish (Wilson, 1977); protein: 3.5 kcal/g; fat: 8.1 kcal/g; NFE: 2.5 kcal/g.
Treatments This experiment consisted of five treatments with two replications per treatment. The treatments were assigned randomly using a completely randomized design. The fish in two aquaria were given each of the experimental diets containing various levels of protein. Management Milkfish fry were fed twice daily (half of the ration at 9.00 a.m. and half at 5.00 p.m.), 7 days per week at a rate of 10% (dry matter) of their body weight per day. Fish were weighed and counted every 10 days to record weight gain and survival rate. Feed allowances were changed every 10 days. Calculations of total feed allowances were initially based on the average weight of fish in all treatments. Thereafter, they were adjusted, based on the average weight of fish in each treatment and the number of fish in each aquarium.
198
The water in all aquaria was changed twice daily at 8.00 a.m. and at 4.00 p.m. before the fish were fed. Only one-half of the water was changed each time. All aquaria were cleaned thoroughly every morning before the removal of water. The volume of water in each aquarium was adjusted to the number of fish present. Water temperature and salinity were measured twice daily, morning and afternoon, after the water had been changed, and before the fish were fed. The fish were given the experimental diets for a period of 30 days. RESULTS
The growth curves of milkfish fry fed on the experimental diets containing various levels of protein for a period of 30 days are presented in Fig. 1. The
,200
t
Protan
01
0
I
10 Time (days
ievel5
I
I
20
30
1
Fig. 1. Growth curve for milkfish fry fed diets containing various levels of protein.
progressive increase in growth rate of fish appeared to be directly related to the levels of the protein in the diets up to 40%, above which a decline in growth was observed. Fish fed the diets containing 50 and 60% protein grew slower than those fed the 40% protein diet. Milkfish fry which were fed the 40% protein diet had the highest average weight gain (134.7 mg). This weight gain was significantly higher (P < 0.05) than those fed 20 and 30% protein diets, which had weight gains of 43.3 and 65.5 mg, respectively (Table II and Fig. 2). Fish which were fed the two highest levels, 50 and 60% protein, showed lower weight gains (112.3 and 110.0 mg) compared to those receiving the diet containing 40% protein. Feed efficiency expressed in feed conversion values is a reflection of the
199 TABLE II Weight gains, diet conversions and survival rates for milkfish (Chanos chanos) fry fed various dietary levels of protein* Dietary levels of protein (%)
wt gain per fish (mg)
Diet conversion
Survival rate (%)
20 30 40 50 60
43.3= 65.5= 134.7b 112.3b llO.Ob
2.46a 2.20a 1.96a 1.9ga 2.02a
7.5= 12.5a 30.0a 27.5a 28.8a
*Treatment
means with the same superscript are not statistically different at P < 0.05.
140
134.7
120
110.0 112.3
100 % E ; 60 .^ 1 .v' L $
656
60-
30
Protein
40
60
60
levels in diet (%)
Fig. 2. Relationship between weight gains of milkfish fry and the dietary levels of protein.
weight gain (Table II). The best feed conversion of 1.96 was obtained for the 40% protein diet. However, no statistical difference (P < 0.05) was found among fish which were fed various dietary levels of protein. Nevertheless, those diets with lower of higher than 40% protein tended to be less efficient. There was no incidence of high mortality during this 30-day feeding experiment. The mean survival rates were generally low but was highest (30%) for the group that received the 40% protein diet (Table II). No statistical differences (P < 0.05) were found among treatment means. However, a similar trend to that of weight gain could be discerned. Those fed the 50 and 60% protein diets had survival rates slightly lower than those fed the 40% protein diet, whereas those fed the lower protein levels (20 and 30%) showed the lowest survival rates (27.5 and 28.8% vs 7.5 and 12.5%, respectively).
200
DISCUSSION
The mean weight gains of milkfish fry were directly related to the levels of protein in the diet up to 40%. Fish fed the 40% protein diet had the highest weight gain. Thus, a dietary level of protein of 40% seemed to be optimum for milkfish fry fed at a daily rate of 10% biomass. Similar results were obtained by Dupree and Sneed (1966) with channel catfish (Ictalurus punctatus). They found weight gains of channel catfish fingerlings which were fed diets containing different percentages of casein, gluten or soybean were linear with protein content in diets up to 40% protein. However, Deyoe et al. (1968) reported that 25% was the minimum level of protein for maximum growth of channel catfish fingerlings. Simco and Cross (1966) suggested that a practical diet with 30% protein was the most economical for channel catfish raised in earthen ponds. Love11 (1969) indicated that the optimum level of protein for growth of channel catfish ranged from 25 to 40% of the dry ration. Delong et al. (1958) reported that the protein requirements for chinook salmon fed purified diets in tanks at 8 and 14°C were 40 and 55%, respectively. Halver (1976) generalized that the apparent protein requirements were essentially the same for trout and salmon when raised at the same water temperature and was about 50% for fry, with a reduction in requirement as fish increased in size. He also reported that the protein requirement of salmonids increased with increasing salinity and that the protein requirement of trout increased from 40% at 10 p.p.t. salinity to 45% at 20 p.p.t. The protein requirement for optimum growth of Cyprinus carpio fingerling was determined to be around 40% (Ogino and Saito, 1970). With grass carp (Ctenopharyngodon idellus) fry raised in a controlled environment, Dabrowski (1977) observed maximum weight gain when the dietary level of protein was 43%. Cowey et al. (1972) found that the optimum dietary level of protein requirement for plaice Pleuronectes plutessu, was approximately 50%. The slightly lower weight gains of fish fed the diets containing 50 and 60% protein compared to those fed the 40% protein diet could be due to insufficient non-protein energy in the diets. Prather and Love11(1973) indicated that diets with high levels of protein and low amount of non-protein energy may be toxic to channel catfish. The relatively high mortality in this study may be due to environmental stresses such as high salinity (32-34 p.p.t.) and low water temperature (2528°C) which might have caused the gradual death of milkfish fry. However, the fact that the level of 40% protein supported highest survival rate compared to other protein levels suggests that 40% protein was also adequate to maintain satisfactory resistance of the milkfish fry against environmental stresses. CONCLUSION
Comparison of the protein requirements of warm-water fishes indicated that they vary for different species. Within the same species they vary with the size
201
of fish, water temperature and salinity, stocking density, feeding rate, amount of non-protein energy in the feed, quality of the protein or culture procedures. In the present study, results showed that 40% protein is the optimum dietary level required for maximum growth of milkfish, Chanos chanos fry fed 10% biomass per day in a controlled environment. This quantity was also necessary to maintain fish against environmental stresses. Increasing the dietary levels of protein beyond 40% slightly reduced the growth rate. This could be due to the toxic effect of high protein content in the diets with insufficient non-protein energy as has been reported in channel catfish by Prather and Love11 (1973). ACKNOWLEDGEMENT
This study was supported partially through a grant to the Aquaculture Department by the International Development Research Centre of Canada under Project No. 3 p. 74-0146.
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