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Effects of food ration on growth, condition factor, food conversion efficiency, and net yield of estuary grouper, Epinephelus salmoides Maxwell, cultured in floating net-cages
Aquaculture,
27 (1982)
Elsevier Scientific
273
273-283
Publishing Company, Amsterdam - Printed in The Netherlands
EFFECTS OF FOOD RATION ON GROWTH, CONDITION FACTOR, FOOD CONVERSION EFFICIENCY, AND NET YIELD OF ESTUARY GROUPER, EPINEPHELUS SALMOIDES MAXWELL, CULTURED IN FLOATING NET-CAGES
T.E. CHUA’ and S.K. TENG’ School
of Biological
Sciences,
0044-8486/82/0000-0000/$02.75
Universiti
Sains
Malaysia,
Penang
(Malaysia)
0 1982 Elsevier Scientific Publishing Company
274
cost has also been reduced considerably to US$1.68/kg by stock manipulation. The growth and production of fish in cages are dependent on operational and management functions. One of the important aspects of the operational function is regulating the quantity of feeds required to yield the best growth. This is determined from the intake of feed and observation of the feeding habits of the estuary grouper. Juvenile fish below 150 g are fed daily. Larger fish are given a single feeding every 2 days. As the growth of fish is affected by the ration size, the optimal ration is determined before calculating the feeding schedule of the fish. This paper describes the effects of varying rations on the growth parameters of estuary grouper culture in floating net-cages. MATERIAL
AND METHODS
Experimental
fish
The fish for the present experiments were collected from the shallow bank at the Western Channel of Penang Straits. The fish were kept in floating cages to condition them to the new environment and fed with chopped trash fish. Experiments began after all the fish fed voluntarily on the trash fish. Culture cages
The size of the polyethylene net-cages used for the present study was 1.5 X 1.5 X 1.65 m, with mesh size 12.5 mm. The net-cages were suspended from a floating framework 8.4 X 5.4 m. Details on the construction of the netcages have been described in Chua and Teng (1977) and Chua (1979). Feeds
The trash fish used as feed consisted of anchovy (Engraulis spp.), sciaenids (Pseudosciaena spp.) and small carangids (Selaroides spp.). The food value of the trash fish as feed for groupers has been reported by Teng et al. (1978). Environmental
conditions
Water samples were collected from the culture sites and from inside the cages for determination of salinity, dissolved oxygen content, pH, and water temperature. Methods of analysis for these parameters were given in Teng and Chua (1978). Analysis of data
The data were analysed for calculations of mean weight, condition factor,
275
survival rate, food conversion ratio, coefficient of variation, and net yield. These terms were defined in Chua and Teng (1978,1979). Analysis of variance (two-way ANOVA without replication (Sokal and Rohlf, 1969)), and covariance analysis were used to test the effects of food ration on the various growth parameters (Snedecor and Cochran, 1974). Duncan’s Multiple Range Test was applied to compare the significance of the means of the growth parameters among the various food rations tested (Vann, 1972). Experimental
design
Fish that had been previously acclimatized to feed voluntarily on trash fish were kept in five net-cages. The fish in each net-cage were given different food rations ranging from 2 to 11% wet weight of fish. The fish were fed once in 2 days before sunset (6-7 p.m.). The size and number of fish used for each food ration are shown in Table I. The total food provided under each prescribed food ration was calculated as the product of food ration, mean fish weight and number of fish in the net-cage. The total was adjusted every week after determining the mean weight of 10 fish sampled at random from each cage. The number of fish surviving in each net-cage was recorded every 2 weeks when all the fish were measured for total length (to the nearest 0.1 cm) and body weight (to the nearest 0.1 g). A fine-mesh lift-net of size 0.75 m X 0.75 m was placed at one corner of each of the net-cages and the weighed food given to the fish at this corner. Ten minutes after feeding, the food left on the lift-net was weighed. The difference was the weight of food consumed by the fish. The experiments began on 2 July 1976 and lasted 84 days. TABLE I Initial data for experimental fish Food ration (% wet weight of fish) Prescribed
Size of fish _________~~~
Total length Actual (cm) (mean ? S.D.) Mean S.D.
2 2 23.2 5 5 23.0 8 8 23.0 11 9.1 f 0.41* 23.3 ___.. .*During the period of the experiments, amount of uneaten food was collected consumed by the fish was calculated. **S.D. = Standard deviation.
2.16 2.01 1.98 1.86
-~~~- ~~~~ ...___
Number of fish
Body weight (9) Mean ___~____
S.D.** .__..
195.1 56.13 50 192.5 50.05 50 189.5 44.24 50 195.5 40.16 50 ______ the prescribed 11% ration was in excess. The using a fine-mesh lift-net and the actual amount
276 RESULTS
The data indicated that there was an increase in the mean weight of fish with corresponding increase in ration size (Fig. 1). The difference was most significant when the food ration was increased from 2 to 5% body weight, and above. Above 5% food ration the differences were marginal. The mean weight of fish on 5% food ration showed an increase of 59.2% over fish on 2% ration, but a decrease of 10.7 and 16.1% over those on the higher rations. The condition factors of the fish on the higher rations increased with time. However, the differences were not statistically significant (P2 0.05; Table II). The condition factor of fish fed on the 2% ration decreased con-
235 i
_. 0
14
26
42
56
Time
(days)
70
64
Fig. 1. Mean fish weights with different food rations. TABLE II The condition factors with different food rations __ Time (days)
0
14 28 42 56 70 84 -_-~
Food ration (% wet weight of fish) 2
5
8
9.1
15.62 15.59 15.31
15.82 16.16 16.43
15.60 15.89 16.37
15.46 15.64 15.97
15.01 15.06 15.00 14.80 _
16.61 16.65 16.68 16.61
16.34 16.58 16.60 16.75
16.02 16.41 16.51 16.61
-._-.-
TABLE III Survival rate (%) with different food rations -._ Time (days)
Food ration (% wet weight of fish) _._
__~ 0 14 28 42 56 70 84
2
5
8
100 100 100 98 98 94 94
100 100 100 100 100 98 98
100 100 100 100 98 98 98
100 100 100 98 96 96 96
sistently with time and was significantIy lower than those for fish on higher food rations (P < 0.05; Table II). The differences in survival rates between the four tests were not significant (Table III; P Z 0.05). Under the experimental conditions, the survival rate of fish did not appe;lr to be affected by the quantity and quality of food rations offered. The relationship between the food conversion ratio, or the food conversion efficiency [(wet weight gained by fish/wet weight of food eaten) X 1001, and the ration size is given in Fig. 2. The solid curve represents the food conversion efficiency, while the broken curve indicates the food conversion ratio. Each point (solid or open) is the mean of 6 bi-weekly measurements with the standard deviation. From the curves, Y, = 7.7713 - 1.6777X Y, = 2.6437
+ 10.2047X
+ 0.1448X’; - 0.0950X2;
r2 = 0.9016,
P < 0.05
r2 = 0.9172, P < 0.05
where, Y, = food conversion ratio; Y, = food conversion and X = food ration (% wet weight of fish).
Food
ration
1%
wet
weight
efficiency
(%);
01 fish)
Fig. 2. The relationship between the food conversion ratio or food conversion efficiency and the food ration.
278
I
2 Food
3 ration
4 (%
5
6
wet
weight
7
6
9
IO
of ftsh)
Fig. 3. The relationship between growth rates and food rations. X, = maintenance food ration; Xz = optimum food ration; X, = maximum food ration.
Note that 5.75% is the food ration that yields the lowest food conversion ratio ( Y1 = 2.91) or the highest food conversion efficiency ( YZ = 31.4%). The relationship is parabolic. Thus, the food conversion ratio was high for the low ration, and vice versa. The maximum efficiency of food conversion, or the lowest food conversion ratio, was determined from Fig. 2 at a ration of 5.75% wet weight of fish. There is a curvilinear relationship between the growth rates (g/fish per day) and the ration size tested, as shown in Fig. 3. This relationship enables the determination of the optimum, maintenance, and maximum food rations for the estuary grouper. The optimum food ration is defined by Brett et al. (1969), and Elliott (1975a), as that ration providing the greatest growth for the least intake of food, and can be determined by drawing the tangent to the growth curve from the origin. The maintenance ration is that ration which just maintains the fish without any weight change, and the maximum ration is that ration which gives the maximum growth rate. Hence, the maintenance, optimum, and maximum food rations of estuary groupers were determined from the growth curve in Fig. 3 to be 1.41, 5.75 and 9.0% respectively. The optimum ration coincides with the greatest efficiency of food conversion as shown in Fig. 2. The variations of fish size in respect to length and weight for each ration, as determined by the coefficients of variation (C.V.), are shown in Table IV. At the end of the experiments, the highest increase in C.V. values was recorded at the ration of 2% and 9.1%. The results indicated that the distribution of fish size was more even at food rations between 5 and 8%. Net yields per cage were affected by the amount of food fed to the fish. At the end of the experiments, the net yields per cage were much higher at rations of 5, 8 and 9.1% than that of 2%, yielding 8.63,10.94,11.53 and
279
TABLE IV Variation of length (L) and weight (W) in relation to ration levels determined by the coefficient of variation (%) __.. Food ration (% wet weight) -~ 2
-_. Initial Final Difference -
~__-
-
5
8
9.1
L
W
L
W
L
W
L
W
9.31 14.98
28.77 43.82
8.74 12.62
26.00 43.27
8.61 10.79
23.31 31.44
7.98 11.00
20.54 32.17
5.67
15.05
3.88
8.21
2.18
8.13
3.02
11.63
-
1.24 kg per cage respectively. The percentage increase in net yield of fish
on 5% ration over the 2% ration was 596%, whilst the difference between net yield on rations above 5% was 26.8-33.6%. The changes in selected water quality parameters within and outside the net-cages monitored throughout the experiments were minimal. Water temperature was 30.3 + l”C, dissolved oxygen content 4.55 + 0.56 cc/l, salinity 30.69 f 0.77 ppt, and pH 8.2 + 0.2. Therefore, the experimental fish were studied in a relatively constant environment with minimal changes in water quality. CONCLUSION
The fish were given four prescribed food rations ranging from 2 to 11% wet weight of fish. The rations were given once in 2 days, which was determined earlier to be the optimum feeding frequency. Brett and Shelbourn (1975) hypothesized that a restricted ration would result in a fixed growth rate until size of fish became a limiting factor, reducing food demand below the prescribed level and thereby reducing growth rate. The hypothesis was verified from their study on the young sockeye salmon (Oncorhynchus nerha) for a period of 7 months. These interactions between fish size and ration level were not observed in the present study, due probably to the short period (84 days) of the experiments. The specific growth rate of the estuary grouper showed consistent differences between the food rations tested, declining at food ration between 5 and 9.1% body weight with the time of culture. The magnitude of decrease, however, was not appreciable (Fig. 3). As the growth rates for each ration were relatively constant with time, the mean growth rates (g/fish per day) were plotted against the range of food rations tested and a growth curve constructed. The average maintenance, optimum, and maximum food rations were determined geometrically from this growth curve (c.f. Brett et al., 1969; Elliott, 1975a) to be respectively 1.41, 5.75, and
Fish
weight
(g)
Fig. 4. The relationship between fish weight and satiation food intake in estuary groupers: intake on chopped trash fish (Engraulis mystax).
9.0% wet weight of fish for estuary groupers at a size range of 190-444 g for water temperatures of 30.3-30.5”C. The maximum food ration determined for the estuary groupers was relatively close to the satiation food intake (Fig. 4) for the size range of fish studied. The optimum food ration (5.75%) is equivalent to approximately 64% the maximum food ration, and about 61% the average satiation food ration. In yellowtail (Seriola quinqeradiata), the average maintenance, optimum, and maximum food rations were determined to be respectively 2.5, 11.5 and 17.5% wet weight of fish per day with fish of 66-500 g cultured in floating net-cages for water temperatures of 26-30.2” C (Harada, 1965). The optimum food ration of yellowtail is equivalent to approximately 66% the maximum food ration, a similar value to that for groupers. However, both the maintenance and optimum food rations in yellowtail are higher than those recorded for the estuary groupers. Although both the yellowtail and estuary groupers are carnivorous fish, the yellowtail is an active fish while estuary groupers are inactive. The metabolism of an active fish is high (Brett, 1962), and therefore requires a greater amount of food to maintain its body activities (Webb, 1978). It is apparent that both maintenance and optimum food rations vary with species, size, and water temperature (Hatanaka et al., 1956; Brett et al., 1969; Tyler and Dunn, 1976; Elliott, 1975a; Frame, 1972). Size of food ration affects the food conversion efficiency or gross conversion efficiency in fish. The gross conversion efficiency is the inverse of food conversion ratio and is expressed either in percentage (Pandian, 1967), or in a proportion between zero and one (Windell and Bowen, 1978). In most studies in fishes, the gross conversion efficiency is found to increase with increase in ration size, from near-maintenance levels to a maximum at an intermediate level, then remains largely unchanged or decreases if the ration is further increased (e.g. Harada, 1965; Brett et al., 1969; Andrews and
281
Stickney, 1972; Brett and Shelbourn, 1975; Elliott, 1975b; Staples and Nomura, 1976; Wurtsbaugh and Davis, 1977a, b). In some cases, the gross conversion efficiency reaches maximum at about two-thirds the maximum ration and then declines (Harada, 1965; Warren and Davis, 1967; Brett and Shelbourn, 1975). This relationship is well illustrated in the present study. Maximum gross conversion efficiency was recorded at the optimum ration (5.75%), which is approximately two-thirds the maximum ration (9.0%) determined for estuary groupers. The value for maximum gross efficiency at the optimum ration was 31.40%, and it decreased to 21.18% when the groupers were given a maximum ration equivalent to 9.0% of body weight. Thus, an increase in food ration from the optimum level (i.e. from 5.75% to 9.0%) resulted in a decrease in the gross conversion efficiency (i.e. from 31.40% to 21.18%). Under the present experimental conditions, the fish consumed the repleted rations above the optimum, and this greatly decreased the conversion efficiency. At ration levels below the optimum, the gross conversion efficiencies were also low (Fig. 2). Although more food was consumed, the growth of fish at the repleted rations was not appreciably increased compared with that at the optimum ration (Fig. 1). Warren and Davis (1967) stated that fish fed depleted rations invariably increased their specific dynamic action (SDA); thus, more energy from the ingested food has to be expended in handling the large rations consumed. This increase in SDA decreases the energy available for growth and consequently lowers the conversion efficiency. Webb (1978) stated that the food energy assimilated, minus nitrogenous losses after assimilation, is the energy available for metabolism and growth. Metabolism must be satisfied first and it will deplete stored energy available for growth if the ration ingested is low. This could explain why fish fed with the low ration size in the present study had low food conversion efficiency. Increase in ration size resulted in higher condition factors (Table II) since the fish grow well when the supply of food is adequate. The condition factors at 2% ration decreased consistently with time; this is difficult to explain. One hypothesis is that some of the fish may have lost weight due to inadequate feeding. This is shown by the wider variation in weight recorded at this level (Table IV). Similar results in which condition factors increased with the size of rations have been reported for winter flounder (Tyler and Dunn, 1976). ACKNOWLEDGEMENTS
The authors wish to express their thanks and appreciation to the International Foundation for Science (IFS), Sweden, and the Universiti Sains Malaysia for financial assistance in the present research project.
282 REFERENCES Andrews, J.W. and Stickney, R.R., 1972. Interactions of feeding rates and environmental temperature on growth, food conversion efficiency and body composition of channel catfish. Trans. Am. Fish. Sot., 101: 94-99. Brett, J.R., 1962. Some considerations in the study of respiratory metabolism in fish, particularly salmon. J. Fish. Res. Board Can., 19 (6): 1025-1038. Brett, J.R. and Shelbourn, J.E., 1975. Growth rate of young sockeye salmon, Oncorhynthus nerka, in relation to fish size and ration level. J. Fish. Res. Board Can., 32: 2103-2110. Brett, J.R., Shelbourn, 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. Chua, T.E., 1979. Site selection, structural design, construction management and production of floating cage culture system in Malaysia. International Workshop on Pen and Cage Culture of Fish. 11-12 February 1979, SEAFDEC Aquaculture Department Tigbauan, Iloilo, Philippines, pp. 65-80. Chua, T.E. and Teng, SK., 1977. Floating fishpen for rearing fishes in coastal waters, reservoirs and mining pools in Malaysia. Fish. Bull. Min. Agric. Rural Dev. Malaysia, 20: l-36. Chua, T.E. and Teng, S.K., 1978. Effects of feeding frequency on the growth of young estuary grouper, Epinephelus tauuina (Forskal), cultured in floating net-cages. Aquaculture, 14: 31-47. Chua, T.E. and Teng, S.K., 1979. Relative growth and production of the estuary grouper, Epinephelus salmoides, under different stocking densities in floating net-cages. Mar. Biol., 54: 362-372. Chua, T.E. and Teng, S.K., 1980. Economic production of estuary grouper, Epinephelus salmoides Maxwell, reared in floating net-cages. Aquaculture, 20: 187-228. Elliott, J.M., 1975a. The growth rate of brown trout (Salmo trutta L.) fed on reduced rations. J. Anim. Ecol., 44: 823-842. Elliott, J.M., 197513. Number of meals in a day, maximum weight of food consumed in a day and maximum rate of feeding for brown trout, Salmo trutta L. Freshwater Biol., 5: 287-303. Frame, D.W., 1972. Intake and transformation of food by young winter flounder (Pseudopleuronectes americanus). N.E. Fish. Wildl. Conf., Ellenville, NY, 16 pp. Harada, T., 1965. Studies on propagation of yellowtail (Seriola quinqueradiata T & S) with special reference to relationship between feeding and growth of fish reared in floating net crawl. Mem. Fat. Agric., Kinki Univ., No. 3, 269 pp. Hatanaka, M., Kosaka, M. and Sato, Y., 1956. Growth and food consumption in plaice. Part II. Kareius bicoloratus (Basilewsky). Tohoku J. Agric. Res., 7: 163-1974. Pandian, T.J., 1967. Intake, digestion, absorption and conversion of food in the fishes, Megalops cyprinoides and Ophiocephalus striatus. Mar. Biol., 1: 16-32. Snedecor, G.W. and Cochran, W.G., 1974. Statistical Methods. Iowa State University Press, Ames, IA, 593 pp. Sokal, R.R. and Rohlf, W.G., 1969. Biometry - The Principles and Practice of Statistics in Biological Research. W.H. Freeman and Co., San Francisco, CA, 776 pp. Staples, D.J. and Nomura, M., 1976. Influence of body size and food ration on the energy budget of rainbow trout, Salmo gairdneri Richardson. J. Fish. Biol., 9: 29-43. Teng, S.K. and Chua, T.E., 1978. Effect of stocking density on growth of estuary grouper, Epinephelus salmoides Maxwell, cultured in floating net-cages. Aquaculture, 15: 273-287. Teng, S.K. and Chua, T.E., 1979. Use of artificial hides to increase the stocking density and production of estuary grouper, Epinephelus salmoides Maxwell, reared in floating net-cages. Aquaculture, 16: 219-232.
283 Teng, SK., Chua, T.E. and Lim, P.E., 1978. Preliminary observation on the dietary protein requirement of estuary grouper, Epinephelus salmoides Maxwell, cultured in floating net-cages. Aquaculture, 15: 251-271. Tyler, A.V. and Dunn, R.S., 1976. Ration, growth and measurement of somatic and organic condition in relation to meal frequency in white flounder, Pseudopleuronectes americanus, with hypothesis regarding population homeostasis. J. Fish. Res. Board Can., 33: 63-15. Vann, E., 1972. Fundamentals of Biostatistics. D.C. Heath and Co., London, 1884 pp. Warren, E.W. and Davis, G.E., 1967. Laboratory studies on the feeding, bioenergetics and growth of fish. In: S.P. Gerking (Editor), The Biological Basis of Freshwater Fish Production. Blackwell Scientific Publications, Oxford, pp. 175-214. Webb, P.W., 1978. Partitioning of energy into metabolism and growth. In: S.D. Gerking (Editor), Ecology of Freshwater Fish Production. Blackwell Scientific Publications, Oxford, pp. 184-214. Windell, J.T. and Bowen, S.H., 1978. Methods for study of fish diets based on analysis of stomach contents. In: T. Bagenal (Editor), Methods for Assessment of Fish Production in Freshwater. IBP Handbook No. 3 (Third Edition). Blackwell Scientific Publications, Oxford, pp. 219-254. Wurtsbaugh, W.A. and Davies, G.E., 1977a. Effects of temperature and ration levels on the growth and food conversion efficiency of Salmo gairdneri, Richardson. J. Fish. Biol., 11: 87-98. Wurtsbaugh, W.A. and Davis, G.E., 197713. Effects of fish size and ration level on the growth and food conversion efficiency of rainbow trout, Salmo gairdneri, Richardson. J. Fish. Biol., 11: 99-104.
27 (1982)
Elsevier Scientific
273
273-283
Publishing Company, Amsterdam - Printed in The Netherlands
EFFECTS OF FOOD RATION ON GROWTH, CONDITION FACTOR, FOOD CONVERSION EFFICIENCY, AND NET YIELD OF ESTUARY GROUPER, EPINEPHELUS SALMOIDES MAXWELL, CULTURED IN FLOATING NET-CAGES
T.E. CHUA’ and S.K. TENG’ School
of Biological
Sciences,
0044-8486/82/0000-0000/$02.75
Universiti
Sains
Malaysia,
Penang
(Malaysia)
0 1982 Elsevier Scientific Publishing Company
274
cost has also been reduced considerably to US$1.68/kg by stock manipulation. The growth and production of fish in cages are dependent on operational and management functions. One of the important aspects of the operational function is regulating the quantity of feeds required to yield the best growth. This is determined from the intake of feed and observation of the feeding habits of the estuary grouper. Juvenile fish below 150 g are fed daily. Larger fish are given a single feeding every 2 days. As the growth of fish is affected by the ration size, the optimal ration is determined before calculating the feeding schedule of the fish. This paper describes the effects of varying rations on the growth parameters of estuary grouper culture in floating net-cages. MATERIAL
AND METHODS
Experimental
fish
The fish for the present experiments were collected from the shallow bank at the Western Channel of Penang Straits. The fish were kept in floating cages to condition them to the new environment and fed with chopped trash fish. Experiments began after all the fish fed voluntarily on the trash fish. Culture cages
The size of the polyethylene net-cages used for the present study was 1.5 X 1.5 X 1.65 m, with mesh size 12.5 mm. The net-cages were suspended from a floating framework 8.4 X 5.4 m. Details on the construction of the netcages have been described in Chua and Teng (1977) and Chua (1979). Feeds
The trash fish used as feed consisted of anchovy (Engraulis spp.), sciaenids (Pseudosciaena spp.) and small carangids (Selaroides spp.). The food value of the trash fish as feed for groupers has been reported by Teng et al. (1978). Environmental
conditions
Water samples were collected from the culture sites and from inside the cages for determination of salinity, dissolved oxygen content, pH, and water temperature. Methods of analysis for these parameters were given in Teng and Chua (1978). Analysis of data
The data were analysed for calculations of mean weight, condition factor,
275
survival rate, food conversion ratio, coefficient of variation, and net yield. These terms were defined in Chua and Teng (1978,1979). Analysis of variance (two-way ANOVA without replication (Sokal and Rohlf, 1969)), and covariance analysis were used to test the effects of food ration on the various growth parameters (Snedecor and Cochran, 1974). Duncan’s Multiple Range Test was applied to compare the significance of the means of the growth parameters among the various food rations tested (Vann, 1972). Experimental
design
Fish that had been previously acclimatized to feed voluntarily on trash fish were kept in five net-cages. The fish in each net-cage were given different food rations ranging from 2 to 11% wet weight of fish. The fish were fed once in 2 days before sunset (6-7 p.m.). The size and number of fish used for each food ration are shown in Table I. The total food provided under each prescribed food ration was calculated as the product of food ration, mean fish weight and number of fish in the net-cage. The total was adjusted every week after determining the mean weight of 10 fish sampled at random from each cage. The number of fish surviving in each net-cage was recorded every 2 weeks when all the fish were measured for total length (to the nearest 0.1 cm) and body weight (to the nearest 0.1 g). A fine-mesh lift-net of size 0.75 m X 0.75 m was placed at one corner of each of the net-cages and the weighed food given to the fish at this corner. Ten minutes after feeding, the food left on the lift-net was weighed. The difference was the weight of food consumed by the fish. The experiments began on 2 July 1976 and lasted 84 days. TABLE I Initial data for experimental fish Food ration (% wet weight of fish) Prescribed
Size of fish _________~~~
Total length Actual (cm) (mean ? S.D.) Mean S.D.
2 2 23.2 5 5 23.0 8 8 23.0 11 9.1 f 0.41* 23.3 ___.. .*During the period of the experiments, amount of uneaten food was collected consumed by the fish was calculated. **S.D. = Standard deviation.
2.16 2.01 1.98 1.86
-~~~- ~~~~ ...___
Number of fish
Body weight (9) Mean ___~____
S.D.** .__..
195.1 56.13 50 192.5 50.05 50 189.5 44.24 50 195.5 40.16 50 ______ the prescribed 11% ration was in excess. The using a fine-mesh lift-net and the actual amount
276 RESULTS
The data indicated that there was an increase in the mean weight of fish with corresponding increase in ration size (Fig. 1). The difference was most significant when the food ration was increased from 2 to 5% body weight, and above. Above 5% food ration the differences were marginal. The mean weight of fish on 5% food ration showed an increase of 59.2% over fish on 2% ration, but a decrease of 10.7 and 16.1% over those on the higher rations. The condition factors of the fish on the higher rations increased with time. However, the differences were not statistically significant (P2 0.05; Table II). The condition factor of fish fed on the 2% ration decreased con-
235 i
_. 0
14
26
42
56
Time
(days)
70
64
Fig. 1. Mean fish weights with different food rations. TABLE II The condition factors with different food rations __ Time (days)
0
14 28 42 56 70 84 -_-~
Food ration (% wet weight of fish) 2
5
8
9.1
15.62 15.59 15.31
15.82 16.16 16.43
15.60 15.89 16.37
15.46 15.64 15.97
15.01 15.06 15.00 14.80 _
16.61 16.65 16.68 16.61
16.34 16.58 16.60 16.75
16.02 16.41 16.51 16.61
-._-.-
TABLE III Survival rate (%) with different food rations -._ Time (days)
Food ration (% wet weight of fish) _._
__~ 0 14 28 42 56 70 84
2
5
8
100 100 100 98 98 94 94
100 100 100 100 100 98 98
100 100 100 100 98 98 98
100 100 100 98 96 96 96
sistently with time and was significantIy lower than those for fish on higher food rations (P < 0.05; Table II). The differences in survival rates between the four tests were not significant (Table III; P Z 0.05). Under the experimental conditions, the survival rate of fish did not appe;lr to be affected by the quantity and quality of food rations offered. The relationship between the food conversion ratio, or the food conversion efficiency [(wet weight gained by fish/wet weight of food eaten) X 1001, and the ration size is given in Fig. 2. The solid curve represents the food conversion efficiency, while the broken curve indicates the food conversion ratio. Each point (solid or open) is the mean of 6 bi-weekly measurements with the standard deviation. From the curves, Y, = 7.7713 - 1.6777X Y, = 2.6437
+ 10.2047X
+ 0.1448X’; - 0.0950X2;
r2 = 0.9016,
P < 0.05
r2 = 0.9172, P < 0.05
where, Y, = food conversion ratio; Y, = food conversion and X = food ration (% wet weight of fish).
Food
ration
1%
wet
weight
efficiency
(%);
01 fish)
Fig. 2. The relationship between the food conversion ratio or food conversion efficiency and the food ration.
278
I
2 Food
3 ration
4 (%
5
6
wet
weight
7
6
9
IO
of ftsh)
Fig. 3. The relationship between growth rates and food rations. X, = maintenance food ration; Xz = optimum food ration; X, = maximum food ration.
Note that 5.75% is the food ration that yields the lowest food conversion ratio ( Y1 = 2.91) or the highest food conversion efficiency ( YZ = 31.4%). The relationship is parabolic. Thus, the food conversion ratio was high for the low ration, and vice versa. The maximum efficiency of food conversion, or the lowest food conversion ratio, was determined from Fig. 2 at a ration of 5.75% wet weight of fish. There is a curvilinear relationship between the growth rates (g/fish per day) and the ration size tested, as shown in Fig. 3. This relationship enables the determination of the optimum, maintenance, and maximum food rations for the estuary grouper. The optimum food ration is defined by Brett et al. (1969), and Elliott (1975a), as that ration providing the greatest growth for the least intake of food, and can be determined by drawing the tangent to the growth curve from the origin. The maintenance ration is that ration which just maintains the fish without any weight change, and the maximum ration is that ration which gives the maximum growth rate. Hence, the maintenance, optimum, and maximum food rations of estuary groupers were determined from the growth curve in Fig. 3 to be 1.41, 5.75 and 9.0% respectively. The optimum ration coincides with the greatest efficiency of food conversion as shown in Fig. 2. The variations of fish size in respect to length and weight for each ration, as determined by the coefficients of variation (C.V.), are shown in Table IV. At the end of the experiments, the highest increase in C.V. values was recorded at the ration of 2% and 9.1%. The results indicated that the distribution of fish size was more even at food rations between 5 and 8%. Net yields per cage were affected by the amount of food fed to the fish. At the end of the experiments, the net yields per cage were much higher at rations of 5, 8 and 9.1% than that of 2%, yielding 8.63,10.94,11.53 and
279
TABLE IV Variation of length (L) and weight (W) in relation to ration levels determined by the coefficient of variation (%) __.. Food ration (% wet weight) -~ 2
-_. Initial Final Difference -
~__-
-
5
8
9.1
L
W
L
W
L
W
L
W
9.31 14.98
28.77 43.82
8.74 12.62
26.00 43.27
8.61 10.79
23.31 31.44
7.98 11.00
20.54 32.17
5.67
15.05
3.88
8.21
2.18
8.13
3.02
11.63
-
1.24 kg per cage respectively. The percentage increase in net yield of fish
on 5% ration over the 2% ration was 596%, whilst the difference between net yield on rations above 5% was 26.8-33.6%. The changes in selected water quality parameters within and outside the net-cages monitored throughout the experiments were minimal. Water temperature was 30.3 + l”C, dissolved oxygen content 4.55 + 0.56 cc/l, salinity 30.69 f 0.77 ppt, and pH 8.2 + 0.2. Therefore, the experimental fish were studied in a relatively constant environment with minimal changes in water quality. CONCLUSION
The fish were given four prescribed food rations ranging from 2 to 11% wet weight of fish. The rations were given once in 2 days, which was determined earlier to be the optimum feeding frequency. Brett and Shelbourn (1975) hypothesized that a restricted ration would result in a fixed growth rate until size of fish became a limiting factor, reducing food demand below the prescribed level and thereby reducing growth rate. The hypothesis was verified from their study on the young sockeye salmon (Oncorhynchus nerha) for a period of 7 months. These interactions between fish size and ration level were not observed in the present study, due probably to the short period (84 days) of the experiments. The specific growth rate of the estuary grouper showed consistent differences between the food rations tested, declining at food ration between 5 and 9.1% body weight with the time of culture. The magnitude of decrease, however, was not appreciable (Fig. 3). As the growth rates for each ration were relatively constant with time, the mean growth rates (g/fish per day) were plotted against the range of food rations tested and a growth curve constructed. The average maintenance, optimum, and maximum food rations were determined geometrically from this growth curve (c.f. Brett et al., 1969; Elliott, 1975a) to be respectively 1.41, 5.75, and
Fish
weight
(g)
Fig. 4. The relationship between fish weight and satiation food intake in estuary groupers: intake on chopped trash fish (Engraulis mystax).
9.0% wet weight of fish for estuary groupers at a size range of 190-444 g for water temperatures of 30.3-30.5”C. The maximum food ration determined for the estuary groupers was relatively close to the satiation food intake (Fig. 4) for the size range of fish studied. The optimum food ration (5.75%) is equivalent to approximately 64% the maximum food ration, and about 61% the average satiation food ration. In yellowtail (Seriola quinqeradiata), the average maintenance, optimum, and maximum food rations were determined to be respectively 2.5, 11.5 and 17.5% wet weight of fish per day with fish of 66-500 g cultured in floating net-cages for water temperatures of 26-30.2” C (Harada, 1965). The optimum food ration of yellowtail is equivalent to approximately 66% the maximum food ration, a similar value to that for groupers. However, both the maintenance and optimum food rations in yellowtail are higher than those recorded for the estuary groupers. Although both the yellowtail and estuary groupers are carnivorous fish, the yellowtail is an active fish while estuary groupers are inactive. The metabolism of an active fish is high (Brett, 1962), and therefore requires a greater amount of food to maintain its body activities (Webb, 1978). It is apparent that both maintenance and optimum food rations vary with species, size, and water temperature (Hatanaka et al., 1956; Brett et al., 1969; Tyler and Dunn, 1976; Elliott, 1975a; Frame, 1972). Size of food ration affects the food conversion efficiency or gross conversion efficiency in fish. The gross conversion efficiency is the inverse of food conversion ratio and is expressed either in percentage (Pandian, 1967), or in a proportion between zero and one (Windell and Bowen, 1978). In most studies in fishes, the gross conversion efficiency is found to increase with increase in ration size, from near-maintenance levels to a maximum at an intermediate level, then remains largely unchanged or decreases if the ration is further increased (e.g. Harada, 1965; Brett et al., 1969; Andrews and
281
Stickney, 1972; Brett and Shelbourn, 1975; Elliott, 1975b; Staples and Nomura, 1976; Wurtsbaugh and Davis, 1977a, b). In some cases, the gross conversion efficiency reaches maximum at about two-thirds the maximum ration and then declines (Harada, 1965; Warren and Davis, 1967; Brett and Shelbourn, 1975). This relationship is well illustrated in the present study. Maximum gross conversion efficiency was recorded at the optimum ration (5.75%), which is approximately two-thirds the maximum ration (9.0%) determined for estuary groupers. The value for maximum gross efficiency at the optimum ration was 31.40%, and it decreased to 21.18% when the groupers were given a maximum ration equivalent to 9.0% of body weight. Thus, an increase in food ration from the optimum level (i.e. from 5.75% to 9.0%) resulted in a decrease in the gross conversion efficiency (i.e. from 31.40% to 21.18%). Under the present experimental conditions, the fish consumed the repleted rations above the optimum, and this greatly decreased the conversion efficiency. At ration levels below the optimum, the gross conversion efficiencies were also low (Fig. 2). Although more food was consumed, the growth of fish at the repleted rations was not appreciably increased compared with that at the optimum ration (Fig. 1). Warren and Davis (1967) stated that fish fed depleted rations invariably increased their specific dynamic action (SDA); thus, more energy from the ingested food has to be expended in handling the large rations consumed. This increase in SDA decreases the energy available for growth and consequently lowers the conversion efficiency. Webb (1978) stated that the food energy assimilated, minus nitrogenous losses after assimilation, is the energy available for metabolism and growth. Metabolism must be satisfied first and it will deplete stored energy available for growth if the ration ingested is low. This could explain why fish fed with the low ration size in the present study had low food conversion efficiency. Increase in ration size resulted in higher condition factors (Table II) since the fish grow well when the supply of food is adequate. The condition factors at 2% ration decreased consistently with time; this is difficult to explain. One hypothesis is that some of the fish may have lost weight due to inadequate feeding. This is shown by the wider variation in weight recorded at this level (Table IV). Similar results in which condition factors increased with the size of rations have been reported for winter flounder (Tyler and Dunn, 1976). ACKNOWLEDGEMENTS
The authors wish to express their thanks and appreciation to the International Foundation for Science (IFS), Sweden, and the Universiti Sains Malaysia for financial assistance in the present research project.
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