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Growth, food intake and evacuation rates of grass carp, Ctenopharyngodon idella fry
Aquaculture, 25 (1981) 67-76 Elsevier Scientific Publishing Company,
67 Amsterdam
- Printed
GROWTH, FOOD INTAKE AND EVACUATION CTENOPHAR YNGODON IDELLA FRY
S.S. DE SILVA* *Department
in The Netherlands
RATES OF GRASS CARP,
and D.E.M. WEERAKOON**
of Zoology, Ruhuna University College, Matara (Sri Lanka)
**Ministry of Fisheries, Inland Fisheries Division, Galle Face, Colombo 3 (Sri Lanka) (Accepted
12 November
1980)
ABSTRACT De Silva, S.S. and Weerakoon, D.E.M., 1981. Growth, food intake and evacuation of grass carp, Ctenopharyngodon idella fry. Aquaculture, 25: 67-76.
rates
Grass carp fry ranging in weight from 9 mg to 300 mg were used in experiments to determine their response to diets of coconut meal and a 1:3 mixture, by weight, of coconut meal and zooplankton at 28 and 33” C. The food intake was generally higher in those fry maintained on the mixed diet at 33” C. The rate of growth was always found to be higher in those fry maintained on a mixed diet at 28” C. The rate of weight increase of fry expressed as a percentage of the initial body weight tended to decrease in fry maintained on a diet of coconut meal, whilst the reverse was observed for others. A maximum food conversion ratio of 1.29 was recorded for fry maintained on a mixed diet of coconut meal and zooplankton at 28” C. Fry of grass carp changed from an almost exclusively carnivorous to a herbivorous one at a length of 25-30 mm. The evacuation time was both temperatureand weight-dependent, decreasing with increasing weight at a particular temperature.
INTRODUCTION
Ctenopharyngodon idella (Cuv. B Val), the Chinese grass carp, has come into much prominence and has been the subject of intensive studies during the last decade due to its importance as a cultivable species, particularly in the tropics. Grass carp has been introduced widely (Jhingran and Gopalakrishnan, 1974) throughout the tropical world. Even though the grass carp has been artificially propogated and reared to marketable size in most countries, most of the scientific documentation on this species is limited to adult fish, in particular to aspects related to growth in culture systems (Sinha and Gupta, 1975; Shireman et al., 1977; Venkatesh and Shetty, 1978; Jhingran et al., 1979) and on digestion (van Dyke and Sutton, 1977; Stroband, 1977; Singh et al., 1979). There is very little known on the biology of grass carp in its early stages of life. Dabrowski (1977) studied the protein requirements of grass carp fry, while most of the others
0044-8486/81/0000-0000/$02.50
o 1981 Elsevier
Scientific
Publishing
Company
68
have been on aspects related to fry rearing (Murty et al., 1978; Jhingran et al., 1979). Grass carp were introduced into Sri Lanka in 1977 when a hatchery was established by the Government of the People’s Republic of China in Udawalawe, in the Sabaragamuwa province. The details of the hatchery and layout of fry and brood ponds have been dealt with by Weerakoon (in prep.). This paper is the first in a series of investigations into the biology of the grass carp fry aimed at elucidating the suitability of this species for culture in Sri Lanka. In this paper results of investigations on the growth of grass carp fry, maintained under two dietary regimes and at two temperatures is presented, together with a comparison of the growth of fry in outdoor ponds. In addition to this, investigations relating to the feeding habits of fry in rearing ponds together with results of experiments on digestion are presented. MATERIALS
AND METHODS
Grass carp fry obtained by induced breeding in 1978 and stocked at the rate of 125000-300 000/0.13 ha were used in this study. Fry ranging in length from 10 to 35 mm were netted, anaesthetized in 1: 10 000 MS 222 (Sandoz) and their length and weight determined. The fry were divided in to four size groups: 8-10 mm (Group I), 12-15 mm (Group II), 20-23 mm (Group III) and 29-30 mm (Group IV) for experiments on growth. Each experimental group consisted of 15-30 fry and were introduced into porcelain tanks of 32 X 52 X 18 cm. Experiments were carried out at 28°C (ambient) and at 33”C, the maximum recorded in the rearing ponds; fry being acclimatized over a 24-h period for the latter experiments. The two dietary regimes used were coconut meal (commonly known as poonac) which has a protein content of l&--21% and a mixture of 1 : 3 coconut meal and zooplankton, by wet weight. Fry were fed in excess and left over food was siphoned out after 3-4 h. Approximately half the volume of water in each experimental tank was replenished daily. Constant aeration was provided for all the tanks. Sampling was carried out every fifth to seventh day as far as possible: fish being anaesthetized in MS 222 solution, length and weight determined and reintroduced into the tanks. Table I summarises the experimental details. In addition regular fry samples were netted from the ponds for growth observations. The experiments were carried out for a 20 day period for each group of fry. The food habits of grass carp fry were investigated by netting 30-40 fry from the rearing ponds between 07.00 and 08.00 h and analysing the gut contents; the methodology adopted being that of De Silva (1973). For the digestion experiments methodology described by Perera and De Silva (1978) was adopted. Experiments were carried out at 28 and 33°C and the food material used was filtered zooplankton. Sacrifices were made every 20 min from the commencement of each experiment.
69
TABLE I Summarv of exnerimental conditions
__~
~_~~
Experimental no.
Temperature (“C)
Size group (mm)
Food* regime
No. of fry
% mortality
1 2 3 4 5 6 7 8 9 10
28 28 28 33 33 33 28 28 33 33
12-15 20-23 29-30 12-15 20-23 29-30 08-10 29-30 08-10 29-30
cm cm cm cm em cm
15 20 15 30 35 15 25 15 25 15
Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil
(II) (II) (IV) (II) (III) (IV) (I) (IV) (I) (IV)
cmlzp cm/w cm/w cm/w
*cm, coconut meal; zp, zooplankton.
o-l,,
]
0
, L
,
,
,
,
(
,
,
,
12
8
#
,
,
,,
16
(I
1
20
DAV
Fig. 1. Food consumption/fish/day as a percentage of the initial body weight of grass carp fry in experiments 1, 4, 7 and 9. RESULTS
Food
intake
Daily food intake/fish/day expressed as a percentage of the initial body weight for fry in experiments 1, 4, 7 and 9, randomly selected, is shown in Fig. 1. The food intake as seen from the figure was found to be variable at both
70
temperatures, irrespective of the diet. Generally a day or two of high intake was followed by a decrease and the intake at 33°C was higher than at 28°C. The same trends were apparent in all the experiments. It is also seen that the intake of fry maintained on a mixed diet of coconut meal and zooplankton tended to be higher, most of the time. The mean intake/fish day and mean body weight at each weighing was obtained and the statistical relationship of the former to the body weight of grass carp fry at 28 and 33°C maintained on the two diets were computed and are as follows: coconut meal log Y = 0.92 log W - log 1.31 (28°C) log Y = 0.981 log w - log 1.21 (33OC) coconut
meal/zooplankton
log Y = 0.41 Iog W -log log Y = 0.35 log W-log
1.80 (28°C) 1.85 (33°C)
where Y = mean intake/fish/day (g) and W = body weight (g). Statistical tests carried out indicated that there was no significant difference in the intake of grass carp fry maintained on a particular diet at 28 and 33°C. But the intake was found to differ significantly (P < 1%) between those maintained on different diets. Growth Absolute increase in weight of grass carp fry maintained on different diets at 28 and 33°C is shown in Fig. 2. Also shown in the figure is the increase in weight of fry reared in the outdoor ponds. The most obvious fact that is apparent is the large increase in weight of fry reared in the ponds, which is to be expected (average 0.192 g/day). The rate of increase was almost always lower at 33 than at 28°C. Also the rate of increase tended to decrease with time in fry fed on coconut meal alone as opposed to those fed on the mixed diet. The growth of fry in the ponds was decidedly higher than that of those in the tanks. The statistical relationships describing the growth of fry in experimental tanks are given in Table II. It was found that a linear relationship of Wt = IV, + bt, where Wt and W0 refer to weight (g) at time t and initial weight fitted the data best. Results of statistical tests carried out to test the significance of the rate of growth of fry of similar size (initial) and maintained on the same diet at 28 and 33°C indicated that they were not significantly different from each other. However, the rates of growth of fry maintained on different diets were found to differ significantly from each other at 1% (P< 0.01).
71 061meal/4p uwal *-m-.c 28Cb.--A
+.
. pond
.Q /’
-
3x-
I’ 8’ /’ I’
‘
5
0
DAY
10
20
15
Fig. 2. Mean weight of grass carp fry at each sampling in the different experimental groups, together with that of fry in the rearing ponds. The number of each experiment is indicated against the lines. TABLE
II
Growth equations for each of the experimental groups of fry, the conversion ratio and results of statistical tests carried out to test the significance of the rate of growth of grass carp fry of similar size groups maintained at the same temperature but on different diets (FCR, food conversion ratio) EXP. no. __ .._
Temp.
3 6 6
10
equations
FCR
t
0.23 1.29
Wt = 0.042 Wt = 0.009
+ 0.00076 + 0.00047
33 33
cm cmlzp
Wt = 0.042 Wt = 0.009
+ 0.00046 + 0.0049
t
0.15 1.23
33 28
cm cm
Wt = 0.155
+ 0.0011 + 0.0027
t t
0.12 0.28
28 28
cm
Wt = 0.355
+ 0.005
cm/m
Wt = 0.245
+ 0.013
cm
Wt = 0.355 Wt = 0.245
+ 0.00036 + 0.0085
4
5
Growth
cmlzp
28 28
2
Diet CIll
1 7
9
(‘0
33 33
cm/w
Wt = 0.155
t I t t 1
t t
6.13
20.5
15.14
0.19 1.13
8.82
0.02 9.0
1 t
t 3
72
Food conversion ratio (FCR) The FCR is expressed as a ratio of the food intake (wet weight) to the increase in the mean weight (wet) of fry under each experimental condition. The FCR ranged between 0.185 and 0.230 and 0.020 and 0.150 in fry maintained on a diet of coconut meal at 28 and 33°C respectively, and it varied between 1.13 and 1.29 and 1.04 and 1.23 in fry maintained on a mixed diet of coconut meal and zooplankton at 28 and 33°C respectively. There was a general trend for the percentage conversion efficiency, expressed as the increase per unit intake of food to decrease with increasing size of fry (Fig. 3).
0
004
1
t
0
I
I
I
0.20
12 WEIGHT
I
0 28
I
1 0.36
(g)
Fig. 3. Relationship of the percent conversion efficiency to mean weight of grass carp fry maintained on a coconut meal diet at 28 and 33°C.
Food habits The proportion of different food items occurring in grass carp fry of five length classes, expressed as a percentage of all food items is shown in Fig. 4. Grass carp fry in the early stages of growth tend to feed almost exclusively on zooplankton, primarily on Brachionus sp. There is a gradual change from a carnivorous habit to a herbivorous one at a size of about 25 mm. Fry longer than 25 mm do not appear to feed on zooplankton. It is evident that with the adoption of the herbivorous habit the importance of Pediastrum increases gradually, accounting for nearly 40% of the diet in 30-40 mm long fry. Digestion From the results of each sacrifice
experiment
the time taken for complete
73
80
70 F 50-
-$40kG W
E30-
8 s
20-
lo- 1 I I / I
LENGTH
GROUP (mm
1
Fig. 4. The predominant food items, expressed as a percentage of the total ingested in five length groups of grass carp fry (see De Silva (1973) for the method of calculations).
of the gut was computed by regression analysis (Perera and De Silva, 1978). The time taken for complete evacuation appears to decrease with temperature as well as with size (Fig. 5), the latter contrary to expected results. The evacuation time for grass carp fry varied between 420 and 249 min for fry ranging in weight from 0.06 to 0.36 g at 28°C and between 340 and 225 min for similar size fry at 33” C.
evacuation
DISCUSSION
The day-to-day variation in food intake has been reported for almost all the fish species studied (Brown, 1957; Pandian, 1970; De Silva and Perera, 1976) and the reasons for such variations have been hypothesized by Brown (1957). The statistical relationships for food intake to body weight, for any particular diet, did not differ significantly at the two experimental temperatures of 28 and 33°C. Kinne (1960), however, found the food intake to be significantly different at different temperatures in Cyprinodon naculurius and attributed this to differences in the appetite. Winberg (1956) concluded that under standard conditions particular values for the exponent b of the standard equation of food intake to body weight
Fig. 5. Relationship of the time for complete evacuation of the gut to mean weight of grass carp fry at 28 and 33” C.
Y = aI@ characterises all fish species, being close to 0.8 at standard levels of metabolism. The higher values of the exponent observed in the present study, for the coconut meal diet, possibly indicates that the food material ingested was being primarily utilized for energy rather than growth. Dabrowski and Kozak (1979) also found the growth rate of grass carp fry to be linear, when maintained on a diet of fish meal and soya bean. In the present study the rate of increase in weight of fry maintained on a mixed diet of coconut meal and zooplankton did not appear to decrease with increasing weight, in contrast to those on a diet of coconut meal alone. It is possible that this may be either due to (a) low protein level of coconut meal, (b) presence of growth inhibitory factors in coconut meal and (c) lack or insufficiency of certain essential amino acids. Presence of aflatoxins and similar products have been demonstrated in coconut meal (Samarajeewa et al., 1977) Similarly deficiences of soya bean meal, a commonly used supplementary feed in the tropics, have been noted by Dabrowski and Kozak (1979) and Smith (1977). Stroband (1977) also has reported that animal food stimulates rapid growth in grass carp juveniles. Most reported work on growth of grass carp has been on larger size groups, the closest to the present study being that of Dabrowski and Kozak (1979), where the initial weight
75
of fry used in the experiments was 0.4 g, compared to the range of 9 to 330 mg in this study. Thus itwould be erroneous to compare growth in absolute terms. However, the percentage increases and the FCR reported here are high, and the FCR compares well with a factor of 1.46 reported for Tilapia aurea fry and that reported for grass carp (initial weight 3 g) fed with fresh duck weed (Shireman et al., 1978). Opuszynski (1969) reported that chironomid and zooplankton dominated the food of grass carp fry 36-42 mm long, while Stroband (1977) suggested that they remain carnivorous in the first 7 months after hatching. The present study indicates that grass carp fry exhibited selectivity from the early stages, with a distinct change to a herbivorous diet rather early in life, as also reported by Hickling (1966). The decrease in evaluation time with increasing weight of fry, contrary to expectations, could possibly be due to the inability of the fry to process zooplankton effectively, with growth. This is probably also indicative of a change in both gut morphology and physiology at this stage of growth.
REFERENCES Brown, M.E., 1957. Experiments on studies on growth. In: M. Brown (Editor), Physiology of Fishes. Vol. 1, Academic Press, London, pp. 361-398. Davis, A.T. and Stickney, R.R., 1978. Growth responses of Tilupia aurea to protein dietary quality and quantity. Trans. Am. Fish. Sot., 107: 479-483. Dabrowski, K., 1977. Protein requirements of grass carp fry (Cfenopharyngodon idella Val.). Aquaculture, 12: 63-73. Dabrowski, K. and Kozak, B., 1979. The use of fish meal and soya bean meal as protein source in the diet of grass carp fry. Aquaculture, 18: 107-114. De Silva, S.S., 1973. Food and feeding habits of the herring Clupea harengus and the sprat C. sprattus in inshore waters of the west coast of Scotland. Mar. Biol., 20: 682-690 De Silva, S.S. and Balbontin, F., 1974. Laboratory studies on food intake, growth and food conversion of young herring (Clupea harengus L.). J. Fish Biol., 6: 645-658. De Silva, S.S. and Perera, P.A.B., 1976. Studies on the young grey mullet, Mugil cephalus L. I. Effects of salinity on food intake, growth and food conversion. Aquaculture, 7 : 327-338. Hickling, C.F., 1966. Observations on the growth of the Chinese grass carp Ctenopharyngodon idella C. et Val. Fish. Cult. Res. Stn., Malacca, pp. 43-49. Jhingran, V.G. and Gopalakrishnan, V., 1974, Catalogue of cultivated aquatic organisms. FAO Fish Tech. Pap. No. 130, 83 pp. Jhingran, V.G., Sehgal, K.L., Dumar, K. and Ghosh, B.B., 1979. Rearing advanced fry of major Indian carp species in recirculating-filtering ponds at Barrackpore, West Bengal. Aquaculture, 18: 45-60. Kinne, O., 1960. Growth, food intake and food conversion in a europlastic fish exposed to different temperatures and salinities. Physiol. Zool., 33: 228-317. Murty, D.S., Dey, R.K. and Reddy, P.V.G.K., 1978. Experiments on rearing exotic carp fingerlings in composite fish culture in India. Aquaculture, 13: 331-338. Opuszynski, K., 1972. Use of phytophagous fish to control aquatic plants. Aquaculture, 1: 61-74. Pandian, T.J., 1970. Intake and conversion of food in the fish Limanda limanda, exposed to different temperatures. Mar. Biol., 5: l-17. Perera, P.A.B. and De Silva, S.S., 1978. Studies on the young grey mullet Mugil cephalus L. digestion. Mar. Biol., 44: 383-387.
76 Samarajeewa, U., Arsecularatne, S.N. and Bandunatha, C.H.S.R., 1977. Degradation of aflatoxins in coconut oil and copra meal (poonac). J. Natnl. Sci. Coun. Sri Lanka, 5: 1-12. Shireman, J.V., Colle, D.E. and Rottman, R.W., 1977. Intensive culture of grass carp, Ctenopharyngodon idella, in circular tanks. J. Fish Biol., 11: 267-271. Singh, B.N., Sinha, V.R.P. and Charkraborty, D.P., 1979. Effects of protein quality and temperature on the growth of fingerlings of rohu, Labeo rohita (Hamilton). Proc. World Symp. Finfish Nutr. Fish Technol., 1: 267-271. Sinha, V.R.P. and Gupta, M.V., 1975. On the growth of grass carp Ctenopharyngodon idella Val. in composite fish culture at Dalyani, West Bengal. Aquaculture, 5: 283-290 Smith, R.R., 1977. Recent research invilving full-fat soya bean meal in salmonid diets. Salmonid, 1: 8-l 1. Stroband, H.W.J., 1977. Growth and diet dependent structural adaptation of the digestive tract in juvenile grass carp (Ctenopharyngodon idella Val.). J. Fish Biol., 11: 167-174. Van Dyke, J.M. and Sutton, D.L., 1977. Digestion of duckweed (Lemna sp.) by the grass carp (Ctenopharyngodon idella). J. Fish Biol., 11: 271-278. Venkatesh, B. and Shetty, P.C., 1978. Studies on the growth rate of the grass carp Ctenopharyngodon idella (Valenciennes) fed on two aquatic weeds and a terrestrial grass. Aquaculture, 13: 45-53. Winberg, G.G., 1956. Rate of metabolism and food requirements of fishes. MinskBelorusskogo Nauchnye Trudy Belorussk, Gos. Univ. imeni. V.I. Lenina, 253 pp. (Translation Fish. Res. Board Can., No. 194).
67 Amsterdam
- Printed
GROWTH, FOOD INTAKE AND EVACUATION CTENOPHAR YNGODON IDELLA FRY
S.S. DE SILVA* *Department
in The Netherlands
RATES OF GRASS CARP,
and D.E.M. WEERAKOON**
of Zoology, Ruhuna University College, Matara (Sri Lanka)
**Ministry of Fisheries, Inland Fisheries Division, Galle Face, Colombo 3 (Sri Lanka) (Accepted
12 November
1980)
ABSTRACT De Silva, S.S. and Weerakoon, D.E.M., 1981. Growth, food intake and evacuation of grass carp, Ctenopharyngodon idella fry. Aquaculture, 25: 67-76.
rates
Grass carp fry ranging in weight from 9 mg to 300 mg were used in experiments to determine their response to diets of coconut meal and a 1:3 mixture, by weight, of coconut meal and zooplankton at 28 and 33” C. The food intake was generally higher in those fry maintained on the mixed diet at 33” C. The rate of growth was always found to be higher in those fry maintained on a mixed diet at 28” C. The rate of weight increase of fry expressed as a percentage of the initial body weight tended to decrease in fry maintained on a diet of coconut meal, whilst the reverse was observed for others. A maximum food conversion ratio of 1.29 was recorded for fry maintained on a mixed diet of coconut meal and zooplankton at 28” C. Fry of grass carp changed from an almost exclusively carnivorous to a herbivorous one at a length of 25-30 mm. The evacuation time was both temperatureand weight-dependent, decreasing with increasing weight at a particular temperature.
INTRODUCTION
Ctenopharyngodon idella (Cuv. B Val), the Chinese grass carp, has come into much prominence and has been the subject of intensive studies during the last decade due to its importance as a cultivable species, particularly in the tropics. Grass carp has been introduced widely (Jhingran and Gopalakrishnan, 1974) throughout the tropical world. Even though the grass carp has been artificially propogated and reared to marketable size in most countries, most of the scientific documentation on this species is limited to adult fish, in particular to aspects related to growth in culture systems (Sinha and Gupta, 1975; Shireman et al., 1977; Venkatesh and Shetty, 1978; Jhingran et al., 1979) and on digestion (van Dyke and Sutton, 1977; Stroband, 1977; Singh et al., 1979). There is very little known on the biology of grass carp in its early stages of life. Dabrowski (1977) studied the protein requirements of grass carp fry, while most of the others
0044-8486/81/0000-0000/$02.50
o 1981 Elsevier
Scientific
Publishing
Company
68
have been on aspects related to fry rearing (Murty et al., 1978; Jhingran et al., 1979). Grass carp were introduced into Sri Lanka in 1977 when a hatchery was established by the Government of the People’s Republic of China in Udawalawe, in the Sabaragamuwa province. The details of the hatchery and layout of fry and brood ponds have been dealt with by Weerakoon (in prep.). This paper is the first in a series of investigations into the biology of the grass carp fry aimed at elucidating the suitability of this species for culture in Sri Lanka. In this paper results of investigations on the growth of grass carp fry, maintained under two dietary regimes and at two temperatures is presented, together with a comparison of the growth of fry in outdoor ponds. In addition to this, investigations relating to the feeding habits of fry in rearing ponds together with results of experiments on digestion are presented. MATERIALS
AND METHODS
Grass carp fry obtained by induced breeding in 1978 and stocked at the rate of 125000-300 000/0.13 ha were used in this study. Fry ranging in length from 10 to 35 mm were netted, anaesthetized in 1: 10 000 MS 222 (Sandoz) and their length and weight determined. The fry were divided in to four size groups: 8-10 mm (Group I), 12-15 mm (Group II), 20-23 mm (Group III) and 29-30 mm (Group IV) for experiments on growth. Each experimental group consisted of 15-30 fry and were introduced into porcelain tanks of 32 X 52 X 18 cm. Experiments were carried out at 28°C (ambient) and at 33”C, the maximum recorded in the rearing ponds; fry being acclimatized over a 24-h period for the latter experiments. The two dietary regimes used were coconut meal (commonly known as poonac) which has a protein content of l&--21% and a mixture of 1 : 3 coconut meal and zooplankton, by wet weight. Fry were fed in excess and left over food was siphoned out after 3-4 h. Approximately half the volume of water in each experimental tank was replenished daily. Constant aeration was provided for all the tanks. Sampling was carried out every fifth to seventh day as far as possible: fish being anaesthetized in MS 222 solution, length and weight determined and reintroduced into the tanks. Table I summarises the experimental details. In addition regular fry samples were netted from the ponds for growth observations. The experiments were carried out for a 20 day period for each group of fry. The food habits of grass carp fry were investigated by netting 30-40 fry from the rearing ponds between 07.00 and 08.00 h and analysing the gut contents; the methodology adopted being that of De Silva (1973). For the digestion experiments methodology described by Perera and De Silva (1978) was adopted. Experiments were carried out at 28 and 33°C and the food material used was filtered zooplankton. Sacrifices were made every 20 min from the commencement of each experiment.
69
TABLE I Summarv of exnerimental conditions
__~
~_~~
Experimental no.
Temperature (“C)
Size group (mm)
Food* regime
No. of fry
% mortality
1 2 3 4 5 6 7 8 9 10
28 28 28 33 33 33 28 28 33 33
12-15 20-23 29-30 12-15 20-23 29-30 08-10 29-30 08-10 29-30
cm cm cm cm em cm
15 20 15 30 35 15 25 15 25 15
Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil
(II) (II) (IV) (II) (III) (IV) (I) (IV) (I) (IV)
cmlzp cm/w cm/w cm/w
*cm, coconut meal; zp, zooplankton.
o-l,,
]
0
, L
,
,
,
,
(
,
,
,
12
8
#
,
,
,,
16
(I
1
20
DAV
Fig. 1. Food consumption/fish/day as a percentage of the initial body weight of grass carp fry in experiments 1, 4, 7 and 9. RESULTS
Food
intake
Daily food intake/fish/day expressed as a percentage of the initial body weight for fry in experiments 1, 4, 7 and 9, randomly selected, is shown in Fig. 1. The food intake as seen from the figure was found to be variable at both
70
temperatures, irrespective of the diet. Generally a day or two of high intake was followed by a decrease and the intake at 33°C was higher than at 28°C. The same trends were apparent in all the experiments. It is also seen that the intake of fry maintained on a mixed diet of coconut meal and zooplankton tended to be higher, most of the time. The mean intake/fish day and mean body weight at each weighing was obtained and the statistical relationship of the former to the body weight of grass carp fry at 28 and 33°C maintained on the two diets were computed and are as follows: coconut meal log Y = 0.92 log W - log 1.31 (28°C) log Y = 0.981 log w - log 1.21 (33OC) coconut
meal/zooplankton
log Y = 0.41 Iog W -log log Y = 0.35 log W-log
1.80 (28°C) 1.85 (33°C)
where Y = mean intake/fish/day (g) and W = body weight (g). Statistical tests carried out indicated that there was no significant difference in the intake of grass carp fry maintained on a particular diet at 28 and 33°C. But the intake was found to differ significantly (P < 1%) between those maintained on different diets. Growth Absolute increase in weight of grass carp fry maintained on different diets at 28 and 33°C is shown in Fig. 2. Also shown in the figure is the increase in weight of fry reared in the outdoor ponds. The most obvious fact that is apparent is the large increase in weight of fry reared in the ponds, which is to be expected (average 0.192 g/day). The rate of increase was almost always lower at 33 than at 28°C. Also the rate of increase tended to decrease with time in fry fed on coconut meal alone as opposed to those fed on the mixed diet. The growth of fry in the ponds was decidedly higher than that of those in the tanks. The statistical relationships describing the growth of fry in experimental tanks are given in Table II. It was found that a linear relationship of Wt = IV, + bt, where Wt and W0 refer to weight (g) at time t and initial weight fitted the data best. Results of statistical tests carried out to test the significance of the rate of growth of fry of similar size (initial) and maintained on the same diet at 28 and 33°C indicated that they were not significantly different from each other. However, the rates of growth of fry maintained on different diets were found to differ significantly from each other at 1% (P< 0.01).
71 061meal/4p uwal *-m-.c 28Cb.--A
+.
. pond
.Q /’
-
3x-
I’ 8’ /’ I’
‘
5
0
DAY
10
20
15
Fig. 2. Mean weight of grass carp fry at each sampling in the different experimental groups, together with that of fry in the rearing ponds. The number of each experiment is indicated against the lines. TABLE
II
Growth equations for each of the experimental groups of fry, the conversion ratio and results of statistical tests carried out to test the significance of the rate of growth of grass carp fry of similar size groups maintained at the same temperature but on different diets (FCR, food conversion ratio) EXP. no. __ .._
Temp.
3 6 6
10
equations
FCR
t
0.23 1.29
Wt = 0.042 Wt = 0.009
+ 0.00076 + 0.00047
33 33
cm cmlzp
Wt = 0.042 Wt = 0.009
+ 0.00046 + 0.0049
t
0.15 1.23
33 28
cm cm
Wt = 0.155
+ 0.0011 + 0.0027
t t
0.12 0.28
28 28
cm
Wt = 0.355
+ 0.005
cm/m
Wt = 0.245
+ 0.013
cm
Wt = 0.355 Wt = 0.245
+ 0.00036 + 0.0085
4
5
Growth
cmlzp
28 28
2
Diet CIll
1 7
9
(‘0
33 33
cm/w
Wt = 0.155
t I t t 1
t t
6.13
20.5
15.14
0.19 1.13
8.82
0.02 9.0
1 t
t 3
72
Food conversion ratio (FCR) The FCR is expressed as a ratio of the food intake (wet weight) to the increase in the mean weight (wet) of fry under each experimental condition. The FCR ranged between 0.185 and 0.230 and 0.020 and 0.150 in fry maintained on a diet of coconut meal at 28 and 33°C respectively, and it varied between 1.13 and 1.29 and 1.04 and 1.23 in fry maintained on a mixed diet of coconut meal and zooplankton at 28 and 33°C respectively. There was a general trend for the percentage conversion efficiency, expressed as the increase per unit intake of food to decrease with increasing size of fry (Fig. 3).
0
004
1
t
0
I
I
I
0.20
12 WEIGHT
I
0 28
I
1 0.36
(g)
Fig. 3. Relationship of the percent conversion efficiency to mean weight of grass carp fry maintained on a coconut meal diet at 28 and 33°C.
Food habits The proportion of different food items occurring in grass carp fry of five length classes, expressed as a percentage of all food items is shown in Fig. 4. Grass carp fry in the early stages of growth tend to feed almost exclusively on zooplankton, primarily on Brachionus sp. There is a gradual change from a carnivorous habit to a herbivorous one at a size of about 25 mm. Fry longer than 25 mm do not appear to feed on zooplankton. It is evident that with the adoption of the herbivorous habit the importance of Pediastrum increases gradually, accounting for nearly 40% of the diet in 30-40 mm long fry. Digestion From the results of each sacrifice
experiment
the time taken for complete
73
80
70 F 50-
-$40kG W
E30-
8 s
20-
lo- 1 I I / I
LENGTH
GROUP (mm
1
Fig. 4. The predominant food items, expressed as a percentage of the total ingested in five length groups of grass carp fry (see De Silva (1973) for the method of calculations).
of the gut was computed by regression analysis (Perera and De Silva, 1978). The time taken for complete evacuation appears to decrease with temperature as well as with size (Fig. 5), the latter contrary to expected results. The evacuation time for grass carp fry varied between 420 and 249 min for fry ranging in weight from 0.06 to 0.36 g at 28°C and between 340 and 225 min for similar size fry at 33” C.
evacuation
DISCUSSION
The day-to-day variation in food intake has been reported for almost all the fish species studied (Brown, 1957; Pandian, 1970; De Silva and Perera, 1976) and the reasons for such variations have been hypothesized by Brown (1957). The statistical relationships for food intake to body weight, for any particular diet, did not differ significantly at the two experimental temperatures of 28 and 33°C. Kinne (1960), however, found the food intake to be significantly different at different temperatures in Cyprinodon naculurius and attributed this to differences in the appetite. Winberg (1956) concluded that under standard conditions particular values for the exponent b of the standard equation of food intake to body weight
Fig. 5. Relationship of the time for complete evacuation of the gut to mean weight of grass carp fry at 28 and 33” C.
Y = aI@ characterises all fish species, being close to 0.8 at standard levels of metabolism. The higher values of the exponent observed in the present study, for the coconut meal diet, possibly indicates that the food material ingested was being primarily utilized for energy rather than growth. Dabrowski and Kozak (1979) also found the growth rate of grass carp fry to be linear, when maintained on a diet of fish meal and soya bean. In the present study the rate of increase in weight of fry maintained on a mixed diet of coconut meal and zooplankton did not appear to decrease with increasing weight, in contrast to those on a diet of coconut meal alone. It is possible that this may be either due to (a) low protein level of coconut meal, (b) presence of growth inhibitory factors in coconut meal and (c) lack or insufficiency of certain essential amino acids. Presence of aflatoxins and similar products have been demonstrated in coconut meal (Samarajeewa et al., 1977) Similarly deficiences of soya bean meal, a commonly used supplementary feed in the tropics, have been noted by Dabrowski and Kozak (1979) and Smith (1977). Stroband (1977) also has reported that animal food stimulates rapid growth in grass carp juveniles. Most reported work on growth of grass carp has been on larger size groups, the closest to the present study being that of Dabrowski and Kozak (1979), where the initial weight
75
of fry used in the experiments was 0.4 g, compared to the range of 9 to 330 mg in this study. Thus itwould be erroneous to compare growth in absolute terms. However, the percentage increases and the FCR reported here are high, and the FCR compares well with a factor of 1.46 reported for Tilapia aurea fry and that reported for grass carp (initial weight 3 g) fed with fresh duck weed (Shireman et al., 1978). Opuszynski (1969) reported that chironomid and zooplankton dominated the food of grass carp fry 36-42 mm long, while Stroband (1977) suggested that they remain carnivorous in the first 7 months after hatching. The present study indicates that grass carp fry exhibited selectivity from the early stages, with a distinct change to a herbivorous diet rather early in life, as also reported by Hickling (1966). The decrease in evaluation time with increasing weight of fry, contrary to expectations, could possibly be due to the inability of the fry to process zooplankton effectively, with growth. This is probably also indicative of a change in both gut morphology and physiology at this stage of growth.
REFERENCES Brown, M.E., 1957. Experiments on studies on growth. In: M. Brown (Editor), Physiology of Fishes. Vol. 1, Academic Press, London, pp. 361-398. Davis, A.T. and Stickney, R.R., 1978. Growth responses of Tilupia aurea to protein dietary quality and quantity. Trans. Am. Fish. Sot., 107: 479-483. Dabrowski, K., 1977. Protein requirements of grass carp fry (Cfenopharyngodon idella Val.). Aquaculture, 12: 63-73. Dabrowski, K. and Kozak, B., 1979. The use of fish meal and soya bean meal as protein source in the diet of grass carp fry. Aquaculture, 18: 107-114. De Silva, S.S., 1973. Food and feeding habits of the herring Clupea harengus and the sprat C. sprattus in inshore waters of the west coast of Scotland. Mar. Biol., 20: 682-690 De Silva, S.S. and Balbontin, F., 1974. Laboratory studies on food intake, growth and food conversion of young herring (Clupea harengus L.). J. Fish Biol., 6: 645-658. De Silva, S.S. and Perera, P.A.B., 1976. Studies on the young grey mullet, Mugil cephalus L. I. Effects of salinity on food intake, growth and food conversion. Aquaculture, 7 : 327-338. Hickling, C.F., 1966. Observations on the growth of the Chinese grass carp Ctenopharyngodon idella C. et Val. Fish. Cult. Res. Stn., Malacca, pp. 43-49. Jhingran, V.G. and Gopalakrishnan, V., 1974, Catalogue of cultivated aquatic organisms. FAO Fish Tech. Pap. No. 130, 83 pp. Jhingran, V.G., Sehgal, K.L., Dumar, K. and Ghosh, B.B., 1979. Rearing advanced fry of major Indian carp species in recirculating-filtering ponds at Barrackpore, West Bengal. Aquaculture, 18: 45-60. Kinne, O., 1960. Growth, food intake and food conversion in a europlastic fish exposed to different temperatures and salinities. Physiol. Zool., 33: 228-317. Murty, D.S., Dey, R.K. and Reddy, P.V.G.K., 1978. Experiments on rearing exotic carp fingerlings in composite fish culture in India. Aquaculture, 13: 331-338. Opuszynski, K., 1972. Use of phytophagous fish to control aquatic plants. Aquaculture, 1: 61-74. Pandian, T.J., 1970. Intake and conversion of food in the fish Limanda limanda, exposed to different temperatures. Mar. Biol., 5: l-17. Perera, P.A.B. and De Silva, S.S., 1978. Studies on the young grey mullet Mugil cephalus L. digestion. Mar. Biol., 44: 383-387.
76 Samarajeewa, U., Arsecularatne, S.N. and Bandunatha, C.H.S.R., 1977. Degradation of aflatoxins in coconut oil and copra meal (poonac). J. Natnl. Sci. Coun. Sri Lanka, 5: 1-12. Shireman, J.V., Colle, D.E. and Rottman, R.W., 1977. Intensive culture of grass carp, Ctenopharyngodon idella, in circular tanks. J. Fish Biol., 11: 267-271. Singh, B.N., Sinha, V.R.P. and Charkraborty, D.P., 1979. Effects of protein quality and temperature on the growth of fingerlings of rohu, Labeo rohita (Hamilton). Proc. World Symp. Finfish Nutr. Fish Technol., 1: 267-271. Sinha, V.R.P. and Gupta, M.V., 1975. On the growth of grass carp Ctenopharyngodon idella Val. in composite fish culture at Dalyani, West Bengal. Aquaculture, 5: 283-290 Smith, R.R., 1977. Recent research invilving full-fat soya bean meal in salmonid diets. Salmonid, 1: 8-l 1. Stroband, H.W.J., 1977. Growth and diet dependent structural adaptation of the digestive tract in juvenile grass carp (Ctenopharyngodon idella Val.). J. Fish Biol., 11: 167-174. Van Dyke, J.M. and Sutton, D.L., 1977. Digestion of duckweed (Lemna sp.) by the grass carp (Ctenopharyngodon idella). J. Fish Biol., 11: 271-278. Venkatesh, B. and Shetty, P.C., 1978. Studies on the growth rate of the grass carp Ctenopharyngodon idella (Valenciennes) fed on two aquatic weeds and a terrestrial grass. Aquaculture, 13: 45-53. Winberg, G.G., 1956. Rate of metabolism and food requirements of fishes. MinskBelorusskogo Nauchnye Trudy Belorussk, Gos. Univ. imeni. V.I. Lenina, 253 pp. (Translation Fish. Res. Board Can., No. 194).