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Effects of feeding frequency on the growth of young estuary grouper, Epinephelus tauvina (Forskål), cultured in floating net-cages
Aquaculture, 14 (1978) 31-47 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
EFFECTS OF FEEDING FREQUENCY ESTUARY GROUPER, EPINEPHELUS IN FLOATING NET-CAGES
31
ON THE GROWTH OF YOUNG Z’AUVINA (FORSKAL), CULTURED
CHUA THIA-ENG and TENG SENG-KEH
School of Biological Sciences, Universiti Sains Malaysia, Penang (Malaysia) (Received 5 December 1977; revised 28 February 1978)
ABSTRACT Chua Thia-Eng and Teng Seng-Keh, 1978. Effects of feeding frequency on the growth of young estuary grouper, Epinephelus tauvina (For&l), cultured in floating net-cages.
Aquaculture,
14: 3147.
Studies on the effects of feeding frequency on the growth of young estuary groupers
(Epinephelus tauuina) with initial size ranging from 16.2 to 16.9 Frn in total length were con ducted in floating net-cages. Seven feeding frequencies in the order of one feeding in 5 days, 4 days, 3 days, 2 days, 1 day, two feedings daily and three feedings daily were studied. Optimal growth and good food conversion ratio as well as higher survival rate were obtained in groups fed to satiation with one feeding in 2 days. Weight gains were substantially reduced in groups fed to satiation with one feeding in 5, 4 or 3 days and were not enhanced when the feeding frequencies were increased to two or three feedings daily. The fact that food conversion ratios were similar in fish fed to satiation with one feeding in 5, 4, 3 and 2 days suggests food intake to be important as a growth limiting factor. Total food intake per feeding was appreciably higher in fish fed once in 2 days. The intake of food was found to be closely related to the amount of food remaining in the stomach, intake being maximal when the stomach was empty. The food deprivation time in estuary groupers was found to be about 36 hours at which over 95% of the food was digested and less than 0.5% body weight of food remained in the stomach. Hence, feeding the fllh at 43hour intervals, i.e. once in 2 days, greatly enhanced maximum intake and efficient utilization of the food. INTRODUCTION
Growth of fishes is affected by biotic and abiotic factors. Among them, food is probably the most potent one. In captivity, a fish is restricted in movement and the supply of food solely depends on its captor and its growth is therefore governed by the kind of food given, ration size, frequency of feeding, stocking density, etc. Increasing-the feeding frequency has been reported to improve the growth of fishes. In filefish, puffer, yellowtail and rainbow trout, the daily food ration changed directly with the frequency of feeding (Ishiwata, 1969a,b). Similar results have been reported in other species of fish (Palmer et al., 1951; Kono and Nose, 1971; Andrews and Page, 1975).
32
The present paper attempts to present the results of experiments on the effects of frequency of feeding on the growth of young estuary groupers cultured in floating net-cages. MATERIALS
AND METHODS
Experimental fish
The fish used for the present study were collected from the Middle Bank in the Southern Channel of the Penang Straits. The young groupers were found in shallow waters amongst the green algae, Ulua reticulata, and red algae, Gracilaria spp. and were collected by a beach seine during the peak season from October to December (Chua and Teng, 1977). All the fish caught were immature; adults are found in much deeper water. The ctilture cages
The netrcages used for the culture experiments were contained in a wooden platform of size about 28 X 18 ft. A wooden platform of this size was able to accommodate 8 net-cages, each about 6 ft X 7 ft X 5 ft 6 in in size. Sealed empty plastic cans were used as floats and secured at regular intervals along the periphery of the platform (Fig.1). The net-cage was made of %-in mesh polyethylene netting and was removable from the wooden platform for cleaning, transferring of fish and other maintenance work. The sides of the net-cage were reinforced with polyethylene ropes. The cages were placed in
Fig.1. Floating net-cages used for the feeding experiments with estuary groupers.
33
the Western Channel of the Penang Straits near where the young groupers were found. The general layout and maintenance of the cages were described in an earlier paper by Chua and Teng (1977). Tidal currents made possible free circulation of water in the cage. The food
The fish in the net-cages were fed with chopped trash fish in pieces of approximately l-in. The trash fish used were anchovy (Engrculis), sciaenids (Pseudosciaena) and small carrangids (Seluroides). The chopped pieces were thoroughly mixed before feeding to the experimental fish. The chemical composition and moisture content of the main species of trash fish used were analyzed. Not much variation in their chemical composition and moisture content was found (Table I). Thus, the above species of trash fish were seleckd and used throughout the experiment. TABLE I Chemical composition and moisture content of trash fish used as feed for estuary groupers Species
Eflgmulis mystax Pseudosciaena acuta Selaroides leptolepis
Moisture content (W)
Chemical composition (% dry wt) Protein
Fat
Carbohydrate
Ash
81.56 84.81 63.23
9.20 6.17 6.88
1.16 1.72 4.30
8.08 7.24 5.59
79.58 30.24 71.47
Hydrology of the culture site
Regular water samples were collected inside and outside the cages during the course of the present study. Salinity and water temperature were determined by a portable Beckman’s conductive sahnometer. Water temperature was counter checked by a mercury thermometer. A battery-operated Metrohm Hersan’s pH meter was used to determine the pH value. Dissolved oxygen content was measured by the standard Winkler’s method (Strickland and Parsons, 1972). Data analysis
The data collected were analyzed for the net-yield per cage, mean fish weight, food conversion ratio, fatness and survival rate of the fish. These terms were defined as follows.
34
W0 : initial total weight of fish; wt : total weight of fish surviving at t days. (b) Mean fish weight : the average weight of fish at t days. wet weight of food eaten (c) Food conversion ratio : wet weight gained by fish’ (d) Fatness: \ it: mean weight of fish at t days. vt 3 X 1000 (Harada, 1965) it : mean length of fish at t days. (a) Net-yield per cage: Wt--W.
I
The ‘cube-law’ of the length in this calculation was based on a formula of length-weight relationship of young E. tuuuina caught from the same locality as the fish used in this feeding experiment were collected. The formula is W = 0.01472L2*g841* (N = 334, size range: 35 mm to 285 mm in total length) (Teng and Chua, MS-a). (e) Survival rate::
X 100 1
number of fish surviving at t days. initial number of fish at the N1 : start of experiment.
Nt
:
Statistical analysis
The above growth parameters were subjected to analysis of variance and New Duncan’s Multiple Range Test to determine if the differences in means were statistically significant (Sokal and Rohlf, 1969; Vann, 1972). Experimental design
The fish used for the experiments were acclimatized to the experimental cages for a few weeks until they were able to take in sliced food voluntarily. Fish of approximately the same size were used (Table II) and were randomly allocated to the experimental cages. In each cage, 100 fish were stocked and seven net-cages were used for the whole experiment. The fish in each cage were treated with one of the following seven feeding regimes: Feeding Regime
Notation
3 times daily 2 times daily 1 time daily 1 feeding in 2 days 1 feeding in 3 days 1 feeding in 4 days 1 feeding in 5 days
3/l 2/l l/l l/2 l/3 l/4 l/5
35
TABLE II Feeding frequency, size and number of fish stocked Feeding frequency No. of feeding(s)/day(s)
l/5 l/4 l/3 l/2 l/l 2/l 3/l
No. of fish stocked
Size of fish stocked Mean length (cm)
S.D.*
16.2 16.5 16.4 16.6 16.9 16.6 16.9
1.1 0.7 0.9 0.9 0.7 0.9 0.6
Mean weight
SD.”
(g) 62.0 67.3 64.0 66.4 72.1 67.6 70.3
13.1 11.6 10.6 11.4 11.0 10.1 10.5
100 100 100 100 100 100 100
*Standard deviation of the mean.
The total length (to the nearest 1 mm) and body weight (to the nearest 0.1 g) of all the test fish were measured once a month during the experiment which lasted for three months. In each feeding, the fish were fed with sliced trash fish to satiation. Satiation is reached when excess food given was not taken in lo-15 minutes. Excessive food was collected by a small lift-net placed at one comer of the netcage. Uneaten food was weighed and the difference between the initial weight of food and the weight of uneaten food was taken as the quantity of food consumed by the fish. When the fish were given one feeding in 5, 4, 3 and 2 days and one feeding per day, the food was given between 6 and 7 p.m. If two feedings were given, the fish were fed once between 6 and 7 a.m. and the second time between 6 and 7 p.m. For three feedings a day, the additional feeding was given between noon and 1 p.m. Results of a previous study indicated that estuary groupers in net-cages showed three active feeding periods in the day, namely between 6 and 7 a.m., noon and 1 p.m. and 6 and 7 p.m. Poor feeding activities were observed during the night (Teng and Chua, MS-b). In nature, serranids of the genera Epinephelus, Mycteroperca and Petrometopon were found to feed both day and night, with feeding peaks around sunrise and sunset (Starck and Davis, 1966; Randall, 1967). Experiment
on gastric digestion of food
Gastric digestion of food in estuary groupers was studied by the autopsy method (Windell, 1967). Before the commencement of the experiment, 100 young groupers ranging from 20.5 cm to 27.1 cm in total length that had been previously acclimatized to feed voluntarily on chopped trash fish were kept in a net-cage of size 6 ft X 7 ft X5 ft 6 in %-in mesh) without feeding for two days. Three fish were sampled immediately after feeding and thereafter
36
at regular intervals of time. They were killed, their stomachs dissected and the amount of food in the stomach weighed. Length and weight of the fish were also taken. The amount of food remaining in the stomach was calculated and expressed as a percentage of the wet w-eight of fish (Fig.6). RESULTS
In general, fish in the higher feeding regime grew faster than those in the lower feeding regime. Fig.2 shows a clear segregation of the mean fish weights into two distinct groups. Those with the higher feeding frequency from one to three feedings daily and one feeding in 2 days showed accelerated growth when compared with those feeding once in 3, 4 or 5 days. Among fish with higher feeding frequency, those fed two and three times daily exhibited the best growth. Fish fed once daily did not appear to grow better than those fed once in 2 days. The average growth rates in relation to different feeding frequencies are shown in Table III. The average growth rate over the three months was much higher in the higher feeding regime, varying from 54.5 g per fish per month to 72.9 g per fish per month. The growth rate seemed to fluctuate in those fish which were fed once, twice, or three times daily. Fish fed once in 2 days increased weight at a rate of 58 g per month. The difference in growth rates in the higher frequencies of feeding was minimal as compared to those in the lower feeding regime (Table III). Results of the analysis of variance (F-values) of the effects of feeding fre300 r
O10 Time
of
culture
(days)
Fig.2. Relationship of feeding frequency and mean fish weight in estuary groupers. X ) One feeding in 5 days, (o----o ) one feeding in 4 days@(x‘) one feeding in 3 days, (WV ) one feeding in 2 days, (OF) once daily, (0 -0) twice daily, =) thrice daily. (a-
37
TABLE III Average growth rate per fish (g/month) Month
Feeding frequency
- No. of feeding(s)/day(s)
l/5
l/4
l/3
l/2
l/l
2/l
3/l
1st 2nd 3rd
24.6 25.6 25.0
25.0 25.0 27.4
32.1 38.1 37.8
56.4 58.7 58.7
42.4 66.5 54.5
61.1 74.3 66.9
63.4 86.1 59.2
Average
25.0
26.5
36.2
58.6
54.5
67.6
72.9
TABLE IV Analysis of variance (F-values) of the effects of feeding frequency on the net-yield per cage, mean fish weight, food conversion ratio, fatness and survival rate for the estuary grouper
Feeding frequency
Net-yield per cage
Mean fiih weight
Food conversion ratio
Fatness
Survival rate
13.10* *
5.95**
21.84**
6.19**
6.62**
**p=G 0.01.
quency on the main growth parameters for the estuary groupers are shown in Table IV. The data indicate that the effects of the feeding frequency on the net-yield per cage, mean fish weight, food conversion ratio, fatness and survival rate are statistically significant (P < 0.01). In terms of net-yield per cage, fish in the feeding regime of one feeding in 2 days to three feedings daily gained more weight (15.24-17.12 kg after three months) than those in the lower feeding frequencies (6.87-10.52 kg after three months). In view of the higher mortality suffered in the higher feeding regime, the net-yield per cage over the three months was found to be higher in fish which were fed once in 2 days which suffered the least mortality ( Fig. 3a,d). Fish subjected to the lower feeding regime showed considerable fluctuations in fatness whilst those in the higher feeding regime showed a consistent monthly increase (Fig.3b). The difference in fatness between fish fed with higher feeding frequencies and those in the lower feeding regime was statis? tically significant (Duncan’s Multiple Range Test, at 0.05 level). Within the feeding regimes tested, fish which were fed once in 5 days showed the best food conversion ratio ranging from 2.29 to 3.41 with an average conversion ratio of 2.93. Fish fed once in 2, 3 or 4 days also showed
30 Time
60 of culture
90 (days)
Fig.3. Effect of feeding frequency on net-yield per cage, fatness, food conversion ratio and survival rate in estuary groupers. ) One feeding in 5 days, (o----o) one feeding in 4 days, (A--_A) one feeding (X -X in 3 days, (H ) one feeding in 2 days, (.) once daily, (o----u ) twice daily, .) thrice daily. (.-
good food converison ratio from 3.02 to 3.27 (Fig.3c). The food conversion ratio for fish fed once, twice or three times daily ranged between 4.45 and 4.67. Statistical analysis of food conversion ratio obtained for the different feeding regimes showed a significant difference between fish fed once to three times daily and fish fed once in 2 days to once in 5 days (Duncan’s Multiple Range Test, at 0.05 level). A higher feeding rate seemed to induce higher mortality, viz. 10 to 20% (Fig.4). The survival rate at the lower feeding regime was fairly good, varying
39
from 99 to 95%. The best survival rate was obtained in cages where the fish were fed once in 2 days (Fig. 3d). The net-yield per cage was also highest at this feeding level (Fig.4). Fig.5 shows the relationship between food conversion ratio, weight of food eaten per fish per feeding and weight of food eaten per fish per month. There was a positive correlation between food conversion ratio and quantity of food eaten per fish per month (r = + 0.8908). Although the total quantity of food eaten per fish per month was high at the higher regime, the conversion ratio was rather poor, whilst a good conversion ratio was noted for fish at the lower feeding regime. Although fish were fed to satiation each feeding, the actual quantity of food eaten per feeding in the high feeding regimes was much less than those taken by fish in the lower feeding regimes (Table V). Fish fed once in 2 days showed the best conversion ratio as well as consuming the largest amount of food given per feeding. The amount of food consumed per feeding in fish fed once in 3, 4 or 5 days was about the same and showed insignificant variation. An inverse relationship existed between food conversion ratio and the total weight of food eaten per fish per feeding (r = -0.9596). The quantity of food eaten per fish per feeding was in fact lower in the higher feedingregime whilst a better conversion ratio was obtained in the lower feeding regime. The high consumption rate of food per fish per feeding at the lower feeding regime was found to be associated with the deprivation time of food in the stomach as indicated in the experiment on gastric digestion of food consumed (Fig.6). The fish which ranged between 20.5 cm and 27.1 cm in total length at a water temperature between 29.2”C and 31.5” C required about 35 k 1 hours to completely digest and evacuate food in their stomachs. The graphs in Fig.6 show that the fish required about 11,19 and 27 hours to digest and evacuate 50, 75 and 90% of the food in the stomach, respectively. The length distribution of fish under different feeding frequencies is shown in Fig.7. The distribution histograms for fish in the higher feeding
ItI
ill
543
I
I
2
1 f
Feeding
Frequency-
+
1
1
No.
of
feedIng
/
day(s)
Fig.4. Relationship of net-yield per cage and survival rate at the end of the experiment with estuary groupers subjected to different frequencies of feeding. (X X ) Net-yield, ) survival rate. (0 --0
40
.,
I Pm
e
20-
0o_4oo-j
- 1.0
r
$ ,
- 2.0 8
-3.0
2-
. LII 11 I 143
I 1 5 Feeding
L I ~wuen~y
-
I tl
z kl - 4.0 2
------x-----__________________x 40-
s
‘ji
.
I a i NO. Of feeding(S) / day(S)
- 4.8
I T
Fig. 5. Relationship of food consumption and food conversion ratio in estuary groupers subjected to different frequencies of feeding. ) average weight of food eaten/ Average weight of food eaten/fish/month, (X -X (1,--‘) fish/feeding, (e-e) average food conversion. TABLE V Food consumption of young estuary grouper cultured in floating net-cages with different feeding frequencies Feeding frequency No. of feeding(s)/day(s)
*
l/5
l/4
l/3
l/2
l/1
211
3/l
Total amount of food eaten (kg/month)
1 2 3 A
5.64 6.89 7.43 6.65
7.87 7.96 8.33 8.05
9.34 11.78 12.46 11.19
14.45 17.81 19.55 17.27
13.42 20.98 22.41 18.94
21.14 26.97 28.52 25.54
22.68 23.59 23.76 23.34
Weight of food eaten per fiih (g/month)
1 2 3 A
56.4 69.8 77.4 68.5
78.7 79.6 84.1 81.1
93.4 119.0 127.1 113.6
144.5 179.0 197.5 173.9
136.9 231.8 265.2 217.8
212.5 285.4 318.7 277.8
229.1 263.6 296.2 273.2
Weight of food eaten per fiih per feeding (g)
1 2 3 A
9.4 11.6 12.9 11.3
9.8 10.0 10.5 .lO.l
9.3 11.9 12.7 11.3
9.6 11.9 13.2 11.6
4.6 7.7 8.8 7.0
3.5 5.0 4.8 4.4
2.5 2.9 3.3 2.9
*l, 2, 3 : lst, 2nd and 3rd month, respectively. A, average.
regime are slightly skewed towards the right whilst a normal distribution histogram is obtained for fish fed in the lower feeding frequencies. The modal length for fish fed once in 5 days was found to be 21 cm. The percentage of fish in each feeding regime exceeding 21 cm was found to be 54,66,75,92, 98, 98 and 98% for fish fed once in 5,4,3 and 2 days, once daily, twice
41
daily and three times daily, respectively. A higher percentage of fish attaining the modal length of 21 cm is therefore obvious in fish in the higher feeding regime. Fish that were fed once in 2 days did not vary much from those in the higher feeding frequencies. Table VI shows the changes in the dissolved oxygen content, water temperature, salinity and pH inside and outside the net-cages over the period of the experiment. Fig.8 shows the diurnal changes of the dissolved oxygen content, salinity, pH and water temperature inside and outside the net-cages. Inside the net-cages, the water was found to be saturated with dissolved oxygen from 1200 hours to 0600 hours, with values varying from 3.04 cc/l to 5.24 cc/l, and the lowest oxygen content of 1.27 cc/l was found at 0900 hours. Diurnal fluctuation of salinity was found to vary from 28.93 ppt at 1500 hours to 29.32 ppt at 1200 hours; pH from 7.85 at 0900 hours to 8.38 at 1800 hours; water temperature from 29.5”C at 1800 hours to 30.3”C at 0900 and 1200 hours. Outside the net-cages, diurnal changes in the dissolved oxygen content were found to range from 2.58 cc/l at 0900 hours to 4.53 cc/l at 1800 hours; salinity from 28.85 ppt at 2100 hours to 29.36 ppt at 1200 hours; pH from 7.85 at 0900 and 2100 hours to 8.26 at 1800 hours; water temperature from 29.5“ C at 2400 and 0300 hours to 31.5”C at 1800 hours. No significant variation in these physical and chemical parameters was found inside and outside the net-cages.
c
2
6
‘10
14
18 Time
22
26
30
34
38
(hours)
Fig.6. Rate of gastric digestion in estuary grouper. Curve with broken bars represents the digestion curve calculated from the 2nd degree polynomial equation: Y = 11.7886-0.6477X + 0.0094X, where Y = food remaining in the stomach (% body wt of fish), X = time of autopsy in hours. Curve with solid line indicates the percent of food digested in the stomach calculated by interpolation from the digestion curve. Circles and vertical bars show the mean and standard deviation, respectively, of three fish sampled.
N=95
(53.77.)
N.96
(66.3%)
N=96 (74.5%)
N&4
401(G)
(926%)
N-80(97.5%)
13 14 15 16 17 16 19 20 21 22 23 24 25 .% W 29 29 30 31 Length (cm)
Fig.7. Histograms showing the length distribution of young estuary groupers subjected to different feeding frequencies. A, B, C, D represent the distribution of fish at the feeding frequency of one feeding in 5, 4, 3, 2 days, respectively; E, F, G at one, two and three feedings per day. The percentage in brackets indicates the percent of fish above the size of 21 cm total length, the modal length of fish at the feeding frequency of one feeding in 5 days. Shaded histograms show the distribution of fish at the end of the experiment; unshaded histograms, the initial distribution.
DISCUSSION
There is a positive relation between growth and feeding frequency. Fish in the higher feeding regime, naturally, grow faster, gain in weight and fatness. However, there is a maximum limit to intensive feeding at which the increase is negligible when considering the amount of food given. The present study clearly reveals that fish grew well, increased in weight and fatness and showed good food conversion ratio and higher survival rate when they were fed to satiation once in 2 days. Higher feeding intensity beyond once in 2 days did not show corresponding increase in mean fish weight, net-yield and fatness, but on the contrary tended to lower the survival rates. Although fish
-.
7.9 + 0.1
7.9 +_0.2
30.93+ 0.64
Salinity (PPt)
PH
30.9 f 0.7
Water (“C) temp.3O - g * o - 6
30.87~ 0.63
3.74* 1.21
3.64 f 0.90
Dissolved oxygen content (cc/l)
8.0 +_0.2
31.00* 0.63
31.0 f 0.4
3.42 f 0.88
Feeding frequency - Feeding(s)/day(s) l/5 l/4 113
Inside the net-cages
8.1 * 0.1
31.01+ 0.56
31.1 ?r 0.6
3.60* 1.16
l/2
8.0 f 0.1
30.98 j10.62
31.1 f 0.4
3.48* 1.32
111
7.9 + 0.3
30.99 + 0.60
31.0 f 0.5
3.38 f 0.98
2/l
8.0 f 0.3
30.97 + 0.58
30.9 f 0.5
3.54 f 0.80
3/l
8.0 + 0.1
30.83* 0.59
30.1 +_1.0
4.24 * 0.67
Outside the net-cages
Changes in the dissolved oxygen content, water temperature, salinity and pH inside and outside the net-cages. Each value is the mean + standard deviation of eight measurements taken at intervals of two weeks (from 21 June 1974 to 28 September 1974)
TABLE VI
-
0900
1200
1500
1800 2400 2100 Time (hours)
0300
0600
Fig.8. Diurnal changes of dissolved oxygen content, salinity, pH and water temperature in the culture site. 0-0 : Outside the cage; l - - -0 : Inside the cage.
in the lower feeding regime, i.e. once in 3, 4 and 5 days, showed good food conversion ratio and high consumption rate, the overall growth rate was much lower than those in the higher feeding frequency. Hence, the optimum feeding frequency for groupers is taken as one feeding in 2 days. The optimum feeding frequency may vary with species. In the case of yellowtail, Seriola quinquaradiata T and S, the fish when fed to satiation, grew better with a feeding regime of twice a day (Harada, 1965); in filefish, the optimum frequency of satiation feeding to obtain the highest growth was 2-3 times daily, and for yellowtail l-2 times daily (Ishiwata, 196913); in stripped bass, the growth rate, food conversion and survival rate were greatly enhanced when the fish were fed to satiation 4 times daily (Powell, 1972); optimal growth and food efficiency were obtained in catfish fed to satiation twice a day (Andrews and Page, 1975). The intake of food is affected by the amount of food remaining in the stomach, a maximum being attained when the stomach is empty. The food
45
deprivation time in groupers is found to be about 36 hours at which time over 95% of the food is digested and less than 0.5% body weight of food remained in the stomach. Hence, feeding the fish at 4%hour intervals, i.e. once in 2 days, greatly enhanced maximum intake and efficient utilization of the food. When the feeding interval is prolonged, i.e. one feeding in 72,96 and 120 hours which are equivalent to feeding once in 3,4 and 5 days, there is no appreciable increase in appetite.The maximum intake is about the same as that of fish fed at 48-hour intervals. When feeding frequency increases, the total intake of food per feeding drops considerably due to the capacity of the stomach, ;is most of the food in the stomach is still not digested. The daily rate at which food can be consumed is related to the capacity of the stomach and the rate of digestion (Brett, 1971). The stomach resumes its full capacity when gastric digestion is completed (Brett and Higgs, 1970). A similar observation is also recorded, namely that the satiation amount of fish varies inversely with the amount of food in the stomach and reaches a peak when the stomach content approaches zero (Ishiwata, 1968a,b). The maximum single intake in groupers of sizes ranging between 20.5 cm and 27.1 cm is in the region of 10-13% body weight. This may vary with size as, for example, young sockeye salmon (Oncorhynchus nerka) consumed 3-13s of its body weight while larger fish consumed l-5% of their body weight (Brett, 1971). The maximum intake varies also with the different species (Ivlev, 1961; Beukema, 1968; Magnuson, 1969; Brett, 1971). In sunfish (Lepomis macrochirus), prolonged starvation decreased the intake of food due to some degenerative changes of the pyloric caeca, the site for enzyme production and absorption (Windell, 1966,1967). The appetite of the sunfish increased initially and reached a maximum on the 4th day of starvation but decreased on further prolongation of starvation. The appetite for groupers on 3, 4 and 5 days starvation was still good although there was sign of decline. The poor food conversion ratio at high feeding regime indicates that a portion of the food consumed might have been wasted. Incomplete digestion leads to poor utilization of food. Dawes (1930) found that in Pleuronectes, if a second meal is taken a short interval after the first, the food leaves the stomach and passes down the alimentary tract more quickly; under such circumstances digestion may well be less efficient. He therefore believes that fish supplied with intermediate quantities of food would make better use of it than those given maximum ration. Moore (1941), in his experiment on Apomotis and Perca, found that although fish would accept food more frequently than once per day, the total amount ingested when averaged over several weeks, was no more than if they had been fed only once per day, while fish fed several times daily did not appear to gain weight more rapidly than those fed once per day. Hickling (1962) stated that fish given an unlimited food supply may pass food through the gut faster than fish given limited food. Although the food conversion ratio for fish fed at intervals of 3, 4 and 5 days is somewhat similar to that of feeding once in 2 days, the growth rate is slow due probably to the effect of starvation.
46
The high mortality rate at the higher feeding regime has also been observed by Harada (1965) in yellowtail. During the experiments, there was no noticeable infection in the test fish nor any drastic changes of the environment as illustrated by the hydrology of the culture site during the period of the study. Since the stocking rate for each cage (17-18 fish/m3) was far below that of the optimum stocking density (60 fish/m3, Teng and Chua, MS-c), the high mortality at the higher feeding regime is not due to overcrowding. The possible explanation, therefore, lies in the physiological stress caused by intense feeding. In teleosts, food in the stomach stimulates gastric secretion (Prosser, 1973) and distention of the stomach wall can evoke secretion of gastric juices (Smit, 1967; Kapoor et al., 1975). Fish at the higher feeding regime always have their stomachs distended with food and this may cause over secretion of gastric juices causing physiological disturbances which may weaken the fish. However, this postulation needs further supporting evidence. ACKNOWLEDGEMENTS
The authors wish to express their gratitude to the International Foundation for Sciences (IFS), Sweden and the Universiti Sains Malaysia for providing financial assistance for research on the culture of estuary groupers in floating net-cages. Thanks are also due to Mr Lim Tack Khoon, owner of the present fish farm, for his permission to use some of his facilities in the farm and Mr Ong Liang Seng for typing the manuscript. REFERENCES Andrews, J.W. and Page, J.W., 1975. The effects of frequency of feeding on culture of catfish. Trans. Am. Fish. Sot., 104(2): 317-321. Beukema, J.J., 1968. Predation by the three-spined stickleback (Gastoristeus aculeatus L.). The influence of hunger and experience. Behaviour, 31: l-126. Brett, J.R., 1971. Satiation time, appetite and maximum food intake of sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Board Can., 28: 409-415. Brett, J.R. and Higgs, D.A., 1970. Effects of temperature on the rate of gastric digestion in fingerling sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Board Can., 27: 17671779. Chua Thia-Eng and Teng Seng-Keh, 1977. Floating fishpens for rearing fishes in coastal waters, reservoirs and mining pools in Malaysia. Fisheries Bulletin 20, Ministry of Agriculture, Malaysia, 36 pp. Dawes, B., 1930. The absorption of fats and lipoids in plaice. J. Mar. Biol. ASSOC.U.K., 17: 75-102. Harada, T., 1965. Studies on propagation of yellowtail (Seriola quinquaradiata T & S) with special reference to relationship between feeding and growth of fish reared in floating net crawl. Memoir of the Faculty of Agriculture, Kinki Univ., No.3, 269 pp, Hickling, C.F., 1962. Fish Culture. Faber and Faber, London, 295 pp. Ishiwata, N., 1968a. Ecological studies on the feeding of fishes - III. Degree of hunger and satiation amount. Bull. Jpn. Sot. Sci. Fish., 34(7): 604-607. Ishiwata, N., 1968b. Ecological studies on the feeding of fishes - IV. Satiation curve. Bull. Jpn. Sot. Sci. Fish., 3448): 691-694.
41
Ishiwata, N., 1969a. Ecological studies on the feeding of fishes - VII. Frequency of feeding and satiation amount. Bull. Jpn. Sot. Sci. Fish., 35(10): 979-984. Ishiwata, N., 1969b. Ecological studies on the feeding of fishes - VIII. Frequency of feeding and growth. Bull. Jpn. Sot. Sci. Fish., 35(10): 985-990. Ivlev, V.S., 1961. Experimental Ecology of the Feeding of Fishes. Yale Univ. Press, New Haven, Connecticut, 302 pp. Kapoor, B.G., Smit, H. and Verighina, I.A., 1975. The alimentary canal and digestion in teleosts. Adv. Mar. Biol., 13: 109-239. Kono, H. and Nose, Y., 1971. Relationship between the amount of food taken and growth in fishes - I. Frequency of feeding for maximum daily ration. Bull. Jpn. Sot. Sci. Fish., 37(3): 169-175. Magnuson, J.J., 1969. Digestion and food consumption by skipjack tuna (Kutsuwonus pelamis). Trans. Am. Fish Sot., 98: 379-392. Moore, W.G., 1941. Studies on the feeding habits of fishes. Ecology, 22: 91-96. Palmer, D.D., Robinson, L.A. and Burrows, R.E., 1951. Feeding frequency: its role in the rearing of blueback salmon fingerlings in troughs. Prog. Fish Cult., 13(4): 205-212. Powell, M.R., 1972. Cage and raceway culture of stripped bass in brackish water in Alabama. Proceeding of the 26th Annual Conference of the Southeastern Association of Games and Fish Commissions, 1972, pp. 553-565. Prosser, C.L., 1973. Stimulation of secretion of digestive fluids. In: C.L. Prosser (Editor), Comparative Animal Physiology, Vol. 1. W.B. Saunders Company, London, pp. 154156. Randall, J.E., 1967. Food habits of reef fishes of the West Indies. Stud. Trop. Oceanogr., 5: 665-847. Smit, H., 1967. Influence of temperature on the rate of gastric juice secretion in the brown bullhead, Zctalurus nebulosus. Comp. Biochem. Physiol., 21: 125-132. Sokal, R.R. and Rohlf, F.J., 1969. Biometry - The Principles and Practice of Statistics in Biological Research. W.H. Freeman and Co., San Francisco, 776 pp. Starck, W.A.,II, and Davis, W.P., 1966. Night habits of fishes of Alligator Reef, Florida. Ichthyol. Aquarium J., 38: 313-356. Strickland, J.D.H. and Parsons, T.R., 1972. A practical handbook of seawater analysis. Fish. Res. Board Can., Bulletin 167 (2nd Edition), 310 pp. Teng Seng-Keh and Chua Thia-Eng (MS-a). Length-weight relationship and growth of young estuary grouper (Epinephelus tauuina Forsk%l) caught from the Middle Bank, Penang Straits. Teng Seng-Keh and Chua Thia-Eng (MS-b). Diurnal feeding activities of the estuary grouper (Epinephelus tauvina Forsk%l) in floating net-cages. Teng Seng-Keh and Chua Thia-Eng (MS-c). Effect of stocking density on the growth of estuary grouper (Epinephelus tauuina Forsk?d) cultured in floating net-cages. Vann, E, 1972. Fundamentals of Biostatistics. D.C. Heath and Co., London, 189 pp. Windell, J.T., 1966. Rate of digestion in the bluegill sunfish. Invest. Indiana Lakes Streams, 7: 185-214. Windell, J.T., 1967. Rate of digestion in fishes. In: S.D. Gerking (Editor), The Biological Basis of Freshwater Fish Production. Blackwell Scientific Publications, Oxford, pp. 151-173.
EFFECTS OF FEEDING FREQUENCY ESTUARY GROUPER, EPINEPHELUS IN FLOATING NET-CAGES
31
ON THE GROWTH OF YOUNG Z’AUVINA (FORSKAL), CULTURED
CHUA THIA-ENG and TENG SENG-KEH
School of Biological Sciences, Universiti Sains Malaysia, Penang (Malaysia) (Received 5 December 1977; revised 28 February 1978)
ABSTRACT Chua Thia-Eng and Teng Seng-Keh, 1978. Effects of feeding frequency on the growth of young estuary grouper, Epinephelus tauvina (For&l), cultured in floating net-cages.
Aquaculture,
14: 3147.
Studies on the effects of feeding frequency on the growth of young estuary groupers
(Epinephelus tauuina) with initial size ranging from 16.2 to 16.9 Frn in total length were con ducted in floating net-cages. Seven feeding frequencies in the order of one feeding in 5 days, 4 days, 3 days, 2 days, 1 day, two feedings daily and three feedings daily were studied. Optimal growth and good food conversion ratio as well as higher survival rate were obtained in groups fed to satiation with one feeding in 2 days. Weight gains were substantially reduced in groups fed to satiation with one feeding in 5, 4 or 3 days and were not enhanced when the feeding frequencies were increased to two or three feedings daily. The fact that food conversion ratios were similar in fish fed to satiation with one feeding in 5, 4, 3 and 2 days suggests food intake to be important as a growth limiting factor. Total food intake per feeding was appreciably higher in fish fed once in 2 days. The intake of food was found to be closely related to the amount of food remaining in the stomach, intake being maximal when the stomach was empty. The food deprivation time in estuary groupers was found to be about 36 hours at which over 95% of the food was digested and less than 0.5% body weight of food remained in the stomach. Hence, feeding the fllh at 43hour intervals, i.e. once in 2 days, greatly enhanced maximum intake and efficient utilization of the food. INTRODUCTION
Growth of fishes is affected by biotic and abiotic factors. Among them, food is probably the most potent one. In captivity, a fish is restricted in movement and the supply of food solely depends on its captor and its growth is therefore governed by the kind of food given, ration size, frequency of feeding, stocking density, etc. Increasing-the feeding frequency has been reported to improve the growth of fishes. In filefish, puffer, yellowtail and rainbow trout, the daily food ration changed directly with the frequency of feeding (Ishiwata, 1969a,b). Similar results have been reported in other species of fish (Palmer et al., 1951; Kono and Nose, 1971; Andrews and Page, 1975).
32
The present paper attempts to present the results of experiments on the effects of frequency of feeding on the growth of young estuary groupers cultured in floating net-cages. MATERIALS
AND METHODS
Experimental fish
The fish used for the present study were collected from the Middle Bank in the Southern Channel of the Penang Straits. The young groupers were found in shallow waters amongst the green algae, Ulua reticulata, and red algae, Gracilaria spp. and were collected by a beach seine during the peak season from October to December (Chua and Teng, 1977). All the fish caught were immature; adults are found in much deeper water. The ctilture cages
The netrcages used for the culture experiments were contained in a wooden platform of size about 28 X 18 ft. A wooden platform of this size was able to accommodate 8 net-cages, each about 6 ft X 7 ft X 5 ft 6 in in size. Sealed empty plastic cans were used as floats and secured at regular intervals along the periphery of the platform (Fig.1). The net-cage was made of %-in mesh polyethylene netting and was removable from the wooden platform for cleaning, transferring of fish and other maintenance work. The sides of the net-cage were reinforced with polyethylene ropes. The cages were placed in
Fig.1. Floating net-cages used for the feeding experiments with estuary groupers.
33
the Western Channel of the Penang Straits near where the young groupers were found. The general layout and maintenance of the cages were described in an earlier paper by Chua and Teng (1977). Tidal currents made possible free circulation of water in the cage. The food
The fish in the net-cages were fed with chopped trash fish in pieces of approximately l-in. The trash fish used were anchovy (Engrculis), sciaenids (Pseudosciaena) and small carrangids (Seluroides). The chopped pieces were thoroughly mixed before feeding to the experimental fish. The chemical composition and moisture content of the main species of trash fish used were analyzed. Not much variation in their chemical composition and moisture content was found (Table I). Thus, the above species of trash fish were seleckd and used throughout the experiment. TABLE I Chemical composition and moisture content of trash fish used as feed for estuary groupers Species
Eflgmulis mystax Pseudosciaena acuta Selaroides leptolepis
Moisture content (W)
Chemical composition (% dry wt) Protein
Fat
Carbohydrate
Ash
81.56 84.81 63.23
9.20 6.17 6.88
1.16 1.72 4.30
8.08 7.24 5.59
79.58 30.24 71.47
Hydrology of the culture site
Regular water samples were collected inside and outside the cages during the course of the present study. Salinity and water temperature were determined by a portable Beckman’s conductive sahnometer. Water temperature was counter checked by a mercury thermometer. A battery-operated Metrohm Hersan’s pH meter was used to determine the pH value. Dissolved oxygen content was measured by the standard Winkler’s method (Strickland and Parsons, 1972). Data analysis
The data collected were analyzed for the net-yield per cage, mean fish weight, food conversion ratio, fatness and survival rate of the fish. These terms were defined as follows.
34
W0 : initial total weight of fish; wt : total weight of fish surviving at t days. (b) Mean fish weight : the average weight of fish at t days. wet weight of food eaten (c) Food conversion ratio : wet weight gained by fish’ (d) Fatness: \ it: mean weight of fish at t days. vt 3 X 1000 (Harada, 1965) it : mean length of fish at t days. (a) Net-yield per cage: Wt--W.
I
The ‘cube-law’ of the length in this calculation was based on a formula of length-weight relationship of young E. tuuuina caught from the same locality as the fish used in this feeding experiment were collected. The formula is W = 0.01472L2*g841* (N = 334, size range: 35 mm to 285 mm in total length) (Teng and Chua, MS-a). (e) Survival rate::
X 100 1
number of fish surviving at t days. initial number of fish at the N1 : start of experiment.
Nt
:
Statistical analysis
The above growth parameters were subjected to analysis of variance and New Duncan’s Multiple Range Test to determine if the differences in means were statistically significant (Sokal and Rohlf, 1969; Vann, 1972). Experimental design
The fish used for the experiments were acclimatized to the experimental cages for a few weeks until they were able to take in sliced food voluntarily. Fish of approximately the same size were used (Table II) and were randomly allocated to the experimental cages. In each cage, 100 fish were stocked and seven net-cages were used for the whole experiment. The fish in each cage were treated with one of the following seven feeding regimes: Feeding Regime
Notation
3 times daily 2 times daily 1 time daily 1 feeding in 2 days 1 feeding in 3 days 1 feeding in 4 days 1 feeding in 5 days
3/l 2/l l/l l/2 l/3 l/4 l/5
35
TABLE II Feeding frequency, size and number of fish stocked Feeding frequency No. of feeding(s)/day(s)
l/5 l/4 l/3 l/2 l/l 2/l 3/l
No. of fish stocked
Size of fish stocked Mean length (cm)
S.D.*
16.2 16.5 16.4 16.6 16.9 16.6 16.9
1.1 0.7 0.9 0.9 0.7 0.9 0.6
Mean weight
SD.”
(g) 62.0 67.3 64.0 66.4 72.1 67.6 70.3
13.1 11.6 10.6 11.4 11.0 10.1 10.5
100 100 100 100 100 100 100
*Standard deviation of the mean.
The total length (to the nearest 1 mm) and body weight (to the nearest 0.1 g) of all the test fish were measured once a month during the experiment which lasted for three months. In each feeding, the fish were fed with sliced trash fish to satiation. Satiation is reached when excess food given was not taken in lo-15 minutes. Excessive food was collected by a small lift-net placed at one comer of the netcage. Uneaten food was weighed and the difference between the initial weight of food and the weight of uneaten food was taken as the quantity of food consumed by the fish. When the fish were given one feeding in 5, 4, 3 and 2 days and one feeding per day, the food was given between 6 and 7 p.m. If two feedings were given, the fish were fed once between 6 and 7 a.m. and the second time between 6 and 7 p.m. For three feedings a day, the additional feeding was given between noon and 1 p.m. Results of a previous study indicated that estuary groupers in net-cages showed three active feeding periods in the day, namely between 6 and 7 a.m., noon and 1 p.m. and 6 and 7 p.m. Poor feeding activities were observed during the night (Teng and Chua, MS-b). In nature, serranids of the genera Epinephelus, Mycteroperca and Petrometopon were found to feed both day and night, with feeding peaks around sunrise and sunset (Starck and Davis, 1966; Randall, 1967). Experiment
on gastric digestion of food
Gastric digestion of food in estuary groupers was studied by the autopsy method (Windell, 1967). Before the commencement of the experiment, 100 young groupers ranging from 20.5 cm to 27.1 cm in total length that had been previously acclimatized to feed voluntarily on chopped trash fish were kept in a net-cage of size 6 ft X 7 ft X5 ft 6 in %-in mesh) without feeding for two days. Three fish were sampled immediately after feeding and thereafter
36
at regular intervals of time. They were killed, their stomachs dissected and the amount of food in the stomach weighed. Length and weight of the fish were also taken. The amount of food remaining in the stomach was calculated and expressed as a percentage of the wet w-eight of fish (Fig.6). RESULTS
In general, fish in the higher feeding regime grew faster than those in the lower feeding regime. Fig.2 shows a clear segregation of the mean fish weights into two distinct groups. Those with the higher feeding frequency from one to three feedings daily and one feeding in 2 days showed accelerated growth when compared with those feeding once in 3, 4 or 5 days. Among fish with higher feeding frequency, those fed two and three times daily exhibited the best growth. Fish fed once daily did not appear to grow better than those fed once in 2 days. The average growth rates in relation to different feeding frequencies are shown in Table III. The average growth rate over the three months was much higher in the higher feeding regime, varying from 54.5 g per fish per month to 72.9 g per fish per month. The growth rate seemed to fluctuate in those fish which were fed once, twice, or three times daily. Fish fed once in 2 days increased weight at a rate of 58 g per month. The difference in growth rates in the higher frequencies of feeding was minimal as compared to those in the lower feeding regime (Table III). Results of the analysis of variance (F-values) of the effects of feeding fre300 r
O10 Time
of
culture
(days)
Fig.2. Relationship of feeding frequency and mean fish weight in estuary groupers. X ) One feeding in 5 days, (o----o ) one feeding in 4 days@(x‘) one feeding in 3 days, (WV ) one feeding in 2 days, (OF) once daily, (0 -0) twice daily, =) thrice daily. (a-
37
TABLE III Average growth rate per fish (g/month) Month
Feeding frequency
- No. of feeding(s)/day(s)
l/5
l/4
l/3
l/2
l/l
2/l
3/l
1st 2nd 3rd
24.6 25.6 25.0
25.0 25.0 27.4
32.1 38.1 37.8
56.4 58.7 58.7
42.4 66.5 54.5
61.1 74.3 66.9
63.4 86.1 59.2
Average
25.0
26.5
36.2
58.6
54.5
67.6
72.9
TABLE IV Analysis of variance (F-values) of the effects of feeding frequency on the net-yield per cage, mean fish weight, food conversion ratio, fatness and survival rate for the estuary grouper
Feeding frequency
Net-yield per cage
Mean fiih weight
Food conversion ratio
Fatness
Survival rate
13.10* *
5.95**
21.84**
6.19**
6.62**
**p=G 0.01.
quency on the main growth parameters for the estuary groupers are shown in Table IV. The data indicate that the effects of the feeding frequency on the net-yield per cage, mean fish weight, food conversion ratio, fatness and survival rate are statistically significant (P < 0.01). In terms of net-yield per cage, fish in the feeding regime of one feeding in 2 days to three feedings daily gained more weight (15.24-17.12 kg after three months) than those in the lower feeding frequencies (6.87-10.52 kg after three months). In view of the higher mortality suffered in the higher feeding regime, the net-yield per cage over the three months was found to be higher in fish which were fed once in 2 days which suffered the least mortality ( Fig. 3a,d). Fish subjected to the lower feeding regime showed considerable fluctuations in fatness whilst those in the higher feeding regime showed a consistent monthly increase (Fig.3b). The difference in fatness between fish fed with higher feeding frequencies and those in the lower feeding regime was statis? tically significant (Duncan’s Multiple Range Test, at 0.05 level). Within the feeding regimes tested, fish which were fed once in 5 days showed the best food conversion ratio ranging from 2.29 to 3.41 with an average conversion ratio of 2.93. Fish fed once in 2, 3 or 4 days also showed
30 Time
60 of culture
90 (days)
Fig.3. Effect of feeding frequency on net-yield per cage, fatness, food conversion ratio and survival rate in estuary groupers. ) One feeding in 5 days, (o----o) one feeding in 4 days, (A--_A) one feeding (X -X in 3 days, (H ) one feeding in 2 days, (.) once daily, (o----u ) twice daily, .) thrice daily. (.-
good food converison ratio from 3.02 to 3.27 (Fig.3c). The food conversion ratio for fish fed once, twice or three times daily ranged between 4.45 and 4.67. Statistical analysis of food conversion ratio obtained for the different feeding regimes showed a significant difference between fish fed once to three times daily and fish fed once in 2 days to once in 5 days (Duncan’s Multiple Range Test, at 0.05 level). A higher feeding rate seemed to induce higher mortality, viz. 10 to 20% (Fig.4). The survival rate at the lower feeding regime was fairly good, varying
39
from 99 to 95%. The best survival rate was obtained in cages where the fish were fed once in 2 days (Fig. 3d). The net-yield per cage was also highest at this feeding level (Fig.4). Fig.5 shows the relationship between food conversion ratio, weight of food eaten per fish per feeding and weight of food eaten per fish per month. There was a positive correlation between food conversion ratio and quantity of food eaten per fish per month (r = + 0.8908). Although the total quantity of food eaten per fish per month was high at the higher regime, the conversion ratio was rather poor, whilst a good conversion ratio was noted for fish at the lower feeding regime. Although fish were fed to satiation each feeding, the actual quantity of food eaten per feeding in the high feeding regimes was much less than those taken by fish in the lower feeding regimes (Table V). Fish fed once in 2 days showed the best conversion ratio as well as consuming the largest amount of food given per feeding. The amount of food consumed per feeding in fish fed once in 3, 4 or 5 days was about the same and showed insignificant variation. An inverse relationship existed between food conversion ratio and the total weight of food eaten per fish per feeding (r = -0.9596). The quantity of food eaten per fish per feeding was in fact lower in the higher feedingregime whilst a better conversion ratio was obtained in the lower feeding regime. The high consumption rate of food per fish per feeding at the lower feeding regime was found to be associated with the deprivation time of food in the stomach as indicated in the experiment on gastric digestion of food consumed (Fig.6). The fish which ranged between 20.5 cm and 27.1 cm in total length at a water temperature between 29.2”C and 31.5” C required about 35 k 1 hours to completely digest and evacuate food in their stomachs. The graphs in Fig.6 show that the fish required about 11,19 and 27 hours to digest and evacuate 50, 75 and 90% of the food in the stomach, respectively. The length distribution of fish under different feeding frequencies is shown in Fig.7. The distribution histograms for fish in the higher feeding
ItI
ill
543
I
I
2
1 f
Feeding
Frequency-
+
1
1
No.
of
feedIng
/
day(s)
Fig.4. Relationship of net-yield per cage and survival rate at the end of the experiment with estuary groupers subjected to different frequencies of feeding. (X X ) Net-yield, ) survival rate. (0 --0
40
.,
I Pm
e
20-
0o_4oo-j
- 1.0
r
$ ,
- 2.0 8
-3.0
2-
. LII 11 I 143
I 1 5 Feeding
L I ~wuen~y
-
I tl
z kl - 4.0 2
------x-----__________________x 40-
s
‘ji
.
I a i NO. Of feeding(S) / day(S)
- 4.8
I T
Fig. 5. Relationship of food consumption and food conversion ratio in estuary groupers subjected to different frequencies of feeding. ) average weight of food eaten/ Average weight of food eaten/fish/month, (X -X (1,--‘) fish/feeding, (e-e) average food conversion. TABLE V Food consumption of young estuary grouper cultured in floating net-cages with different feeding frequencies Feeding frequency No. of feeding(s)/day(s)
*
l/5
l/4
l/3
l/2
l/1
211
3/l
Total amount of food eaten (kg/month)
1 2 3 A
5.64 6.89 7.43 6.65
7.87 7.96 8.33 8.05
9.34 11.78 12.46 11.19
14.45 17.81 19.55 17.27
13.42 20.98 22.41 18.94
21.14 26.97 28.52 25.54
22.68 23.59 23.76 23.34
Weight of food eaten per fiih (g/month)
1 2 3 A
56.4 69.8 77.4 68.5
78.7 79.6 84.1 81.1
93.4 119.0 127.1 113.6
144.5 179.0 197.5 173.9
136.9 231.8 265.2 217.8
212.5 285.4 318.7 277.8
229.1 263.6 296.2 273.2
Weight of food eaten per fiih per feeding (g)
1 2 3 A
9.4 11.6 12.9 11.3
9.8 10.0 10.5 .lO.l
9.3 11.9 12.7 11.3
9.6 11.9 13.2 11.6
4.6 7.7 8.8 7.0
3.5 5.0 4.8 4.4
2.5 2.9 3.3 2.9
*l, 2, 3 : lst, 2nd and 3rd month, respectively. A, average.
regime are slightly skewed towards the right whilst a normal distribution histogram is obtained for fish fed in the lower feeding frequencies. The modal length for fish fed once in 5 days was found to be 21 cm. The percentage of fish in each feeding regime exceeding 21 cm was found to be 54,66,75,92, 98, 98 and 98% for fish fed once in 5,4,3 and 2 days, once daily, twice
41
daily and three times daily, respectively. A higher percentage of fish attaining the modal length of 21 cm is therefore obvious in fish in the higher feeding regime. Fish that were fed once in 2 days did not vary much from those in the higher feeding frequencies. Table VI shows the changes in the dissolved oxygen content, water temperature, salinity and pH inside and outside the net-cages over the period of the experiment. Fig.8 shows the diurnal changes of the dissolved oxygen content, salinity, pH and water temperature inside and outside the net-cages. Inside the net-cages, the water was found to be saturated with dissolved oxygen from 1200 hours to 0600 hours, with values varying from 3.04 cc/l to 5.24 cc/l, and the lowest oxygen content of 1.27 cc/l was found at 0900 hours. Diurnal fluctuation of salinity was found to vary from 28.93 ppt at 1500 hours to 29.32 ppt at 1200 hours; pH from 7.85 at 0900 hours to 8.38 at 1800 hours; water temperature from 29.5”C at 1800 hours to 30.3”C at 0900 and 1200 hours. Outside the net-cages, diurnal changes in the dissolved oxygen content were found to range from 2.58 cc/l at 0900 hours to 4.53 cc/l at 1800 hours; salinity from 28.85 ppt at 2100 hours to 29.36 ppt at 1200 hours; pH from 7.85 at 0900 and 2100 hours to 8.26 at 1800 hours; water temperature from 29.5“ C at 2400 and 0300 hours to 31.5”C at 1800 hours. No significant variation in these physical and chemical parameters was found inside and outside the net-cages.
c
2
6
‘10
14
18 Time
22
26
30
34
38
(hours)
Fig.6. Rate of gastric digestion in estuary grouper. Curve with broken bars represents the digestion curve calculated from the 2nd degree polynomial equation: Y = 11.7886-0.6477X + 0.0094X, where Y = food remaining in the stomach (% body wt of fish), X = time of autopsy in hours. Curve with solid line indicates the percent of food digested in the stomach calculated by interpolation from the digestion curve. Circles and vertical bars show the mean and standard deviation, respectively, of three fish sampled.
N=95
(53.77.)
N.96
(66.3%)
N=96 (74.5%)
N&4
401(G)
(926%)
N-80(97.5%)
13 14 15 16 17 16 19 20 21 22 23 24 25 .% W 29 29 30 31 Length (cm)
Fig.7. Histograms showing the length distribution of young estuary groupers subjected to different feeding frequencies. A, B, C, D represent the distribution of fish at the feeding frequency of one feeding in 5, 4, 3, 2 days, respectively; E, F, G at one, two and three feedings per day. The percentage in brackets indicates the percent of fish above the size of 21 cm total length, the modal length of fish at the feeding frequency of one feeding in 5 days. Shaded histograms show the distribution of fish at the end of the experiment; unshaded histograms, the initial distribution.
DISCUSSION
There is a positive relation between growth and feeding frequency. Fish in the higher feeding regime, naturally, grow faster, gain in weight and fatness. However, there is a maximum limit to intensive feeding at which the increase is negligible when considering the amount of food given. The present study clearly reveals that fish grew well, increased in weight and fatness and showed good food conversion ratio and higher survival rate when they were fed to satiation once in 2 days. Higher feeding intensity beyond once in 2 days did not show corresponding increase in mean fish weight, net-yield and fatness, but on the contrary tended to lower the survival rates. Although fish
-.
7.9 + 0.1
7.9 +_0.2
30.93+ 0.64
Salinity (PPt)
PH
30.9 f 0.7
Water (“C) temp.3O - g * o - 6
30.87~ 0.63
3.74* 1.21
3.64 f 0.90
Dissolved oxygen content (cc/l)
8.0 +_0.2
31.00* 0.63
31.0 f 0.4
3.42 f 0.88
Feeding frequency - Feeding(s)/day(s) l/5 l/4 113
Inside the net-cages
8.1 * 0.1
31.01+ 0.56
31.1 ?r 0.6
3.60* 1.16
l/2
8.0 f 0.1
30.98 j10.62
31.1 f 0.4
3.48* 1.32
111
7.9 + 0.3
30.99 + 0.60
31.0 f 0.5
3.38 f 0.98
2/l
8.0 f 0.3
30.97 + 0.58
30.9 f 0.5
3.54 f 0.80
3/l
8.0 + 0.1
30.83* 0.59
30.1 +_1.0
4.24 * 0.67
Outside the net-cages
Changes in the dissolved oxygen content, water temperature, salinity and pH inside and outside the net-cages. Each value is the mean + standard deviation of eight measurements taken at intervals of two weeks (from 21 June 1974 to 28 September 1974)
TABLE VI
-
0900
1200
1500
1800 2400 2100 Time (hours)
0300
0600
Fig.8. Diurnal changes of dissolved oxygen content, salinity, pH and water temperature in the culture site. 0-0 : Outside the cage; l - - -0 : Inside the cage.
in the lower feeding regime, i.e. once in 3, 4 and 5 days, showed good food conversion ratio and high consumption rate, the overall growth rate was much lower than those in the higher feeding frequency. Hence, the optimum feeding frequency for groupers is taken as one feeding in 2 days. The optimum feeding frequency may vary with species. In the case of yellowtail, Seriola quinquaradiata T and S, the fish when fed to satiation, grew better with a feeding regime of twice a day (Harada, 1965); in filefish, the optimum frequency of satiation feeding to obtain the highest growth was 2-3 times daily, and for yellowtail l-2 times daily (Ishiwata, 196913); in stripped bass, the growth rate, food conversion and survival rate were greatly enhanced when the fish were fed to satiation 4 times daily (Powell, 1972); optimal growth and food efficiency were obtained in catfish fed to satiation twice a day (Andrews and Page, 1975). The intake of food is affected by the amount of food remaining in the stomach, a maximum being attained when the stomach is empty. The food
45
deprivation time in groupers is found to be about 36 hours at which time over 95% of the food is digested and less than 0.5% body weight of food remained in the stomach. Hence, feeding the fish at 4%hour intervals, i.e. once in 2 days, greatly enhanced maximum intake and efficient utilization of the food. When the feeding interval is prolonged, i.e. one feeding in 72,96 and 120 hours which are equivalent to feeding once in 3,4 and 5 days, there is no appreciable increase in appetite.The maximum intake is about the same as that of fish fed at 48-hour intervals. When feeding frequency increases, the total intake of food per feeding drops considerably due to the capacity of the stomach, ;is most of the food in the stomach is still not digested. The daily rate at which food can be consumed is related to the capacity of the stomach and the rate of digestion (Brett, 1971). The stomach resumes its full capacity when gastric digestion is completed (Brett and Higgs, 1970). A similar observation is also recorded, namely that the satiation amount of fish varies inversely with the amount of food in the stomach and reaches a peak when the stomach content approaches zero (Ishiwata, 1968a,b). The maximum single intake in groupers of sizes ranging between 20.5 cm and 27.1 cm is in the region of 10-13% body weight. This may vary with size as, for example, young sockeye salmon (Oncorhynchus nerka) consumed 3-13s of its body weight while larger fish consumed l-5% of their body weight (Brett, 1971). The maximum intake varies also with the different species (Ivlev, 1961; Beukema, 1968; Magnuson, 1969; Brett, 1971). In sunfish (Lepomis macrochirus), prolonged starvation decreased the intake of food due to some degenerative changes of the pyloric caeca, the site for enzyme production and absorption (Windell, 1966,1967). The appetite of the sunfish increased initially and reached a maximum on the 4th day of starvation but decreased on further prolongation of starvation. The appetite for groupers on 3, 4 and 5 days starvation was still good although there was sign of decline. The poor food conversion ratio at high feeding regime indicates that a portion of the food consumed might have been wasted. Incomplete digestion leads to poor utilization of food. Dawes (1930) found that in Pleuronectes, if a second meal is taken a short interval after the first, the food leaves the stomach and passes down the alimentary tract more quickly; under such circumstances digestion may well be less efficient. He therefore believes that fish supplied with intermediate quantities of food would make better use of it than those given maximum ration. Moore (1941), in his experiment on Apomotis and Perca, found that although fish would accept food more frequently than once per day, the total amount ingested when averaged over several weeks, was no more than if they had been fed only once per day, while fish fed several times daily did not appear to gain weight more rapidly than those fed once per day. Hickling (1962) stated that fish given an unlimited food supply may pass food through the gut faster than fish given limited food. Although the food conversion ratio for fish fed at intervals of 3, 4 and 5 days is somewhat similar to that of feeding once in 2 days, the growth rate is slow due probably to the effect of starvation.
46
The high mortality rate at the higher feeding regime has also been observed by Harada (1965) in yellowtail. During the experiments, there was no noticeable infection in the test fish nor any drastic changes of the environment as illustrated by the hydrology of the culture site during the period of the study. Since the stocking rate for each cage (17-18 fish/m3) was far below that of the optimum stocking density (60 fish/m3, Teng and Chua, MS-c), the high mortality at the higher feeding regime is not due to overcrowding. The possible explanation, therefore, lies in the physiological stress caused by intense feeding. In teleosts, food in the stomach stimulates gastric secretion (Prosser, 1973) and distention of the stomach wall can evoke secretion of gastric juices (Smit, 1967; Kapoor et al., 1975). Fish at the higher feeding regime always have their stomachs distended with food and this may cause over secretion of gastric juices causing physiological disturbances which may weaken the fish. However, this postulation needs further supporting evidence. ACKNOWLEDGEMENTS
The authors wish to express their gratitude to the International Foundation for Sciences (IFS), Sweden and the Universiti Sains Malaysia for providing financial assistance for research on the culture of estuary groupers in floating net-cages. Thanks are also due to Mr Lim Tack Khoon, owner of the present fish farm, for his permission to use some of his facilities in the farm and Mr Ong Liang Seng for typing the manuscript. REFERENCES Andrews, J.W. and Page, J.W., 1975. The effects of frequency of feeding on culture of catfish. Trans. Am. Fish. Sot., 104(2): 317-321. Beukema, J.J., 1968. Predation by the three-spined stickleback (Gastoristeus aculeatus L.). The influence of hunger and experience. Behaviour, 31: l-126. Brett, J.R., 1971. Satiation time, appetite and maximum food intake of sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Board Can., 28: 409-415. Brett, J.R. and Higgs, D.A., 1970. Effects of temperature on the rate of gastric digestion in fingerling sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Board Can., 27: 17671779. Chua Thia-Eng and Teng Seng-Keh, 1977. Floating fishpens for rearing fishes in coastal waters, reservoirs and mining pools in Malaysia. Fisheries Bulletin 20, Ministry of Agriculture, Malaysia, 36 pp. Dawes, B., 1930. The absorption of fats and lipoids in plaice. J. Mar. Biol. ASSOC.U.K., 17: 75-102. Harada, T., 1965. Studies on propagation of yellowtail (Seriola quinquaradiata T & S) with special reference to relationship between feeding and growth of fish reared in floating net crawl. Memoir of the Faculty of Agriculture, Kinki Univ., No.3, 269 pp, Hickling, C.F., 1962. Fish Culture. Faber and Faber, London, 295 pp. Ishiwata, N., 1968a. Ecological studies on the feeding of fishes - III. Degree of hunger and satiation amount. Bull. Jpn. Sot. Sci. Fish., 34(7): 604-607. Ishiwata, N., 1968b. Ecological studies on the feeding of fishes - IV. Satiation curve. Bull. Jpn. Sot. Sci. Fish., 3448): 691-694.
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Ishiwata, N., 1969a. Ecological studies on the feeding of fishes - VII. Frequency of feeding and satiation amount. Bull. Jpn. Sot. Sci. Fish., 35(10): 979-984. Ishiwata, N., 1969b. Ecological studies on the feeding of fishes - VIII. Frequency of feeding and growth. Bull. Jpn. Sot. Sci. Fish., 35(10): 985-990. Ivlev, V.S., 1961. Experimental Ecology of the Feeding of Fishes. Yale Univ. Press, New Haven, Connecticut, 302 pp. Kapoor, B.G., Smit, H. and Verighina, I.A., 1975. The alimentary canal and digestion in teleosts. Adv. Mar. Biol., 13: 109-239. Kono, H. and Nose, Y., 1971. Relationship between the amount of food taken and growth in fishes - I. Frequency of feeding for maximum daily ration. Bull. Jpn. Sot. Sci. Fish., 37(3): 169-175. Magnuson, J.J., 1969. Digestion and food consumption by skipjack tuna (Kutsuwonus pelamis). Trans. Am. Fish Sot., 98: 379-392. Moore, W.G., 1941. Studies on the feeding habits of fishes. Ecology, 22: 91-96. Palmer, D.D., Robinson, L.A. and Burrows, R.E., 1951. Feeding frequency: its role in the rearing of blueback salmon fingerlings in troughs. Prog. Fish Cult., 13(4): 205-212. Powell, M.R., 1972. Cage and raceway culture of stripped bass in brackish water in Alabama. Proceeding of the 26th Annual Conference of the Southeastern Association of Games and Fish Commissions, 1972, pp. 553-565. Prosser, C.L., 1973. Stimulation of secretion of digestive fluids. In: C.L. Prosser (Editor), Comparative Animal Physiology, Vol. 1. W.B. Saunders Company, London, pp. 154156. Randall, J.E., 1967. Food habits of reef fishes of the West Indies. Stud. Trop. Oceanogr., 5: 665-847. Smit, H., 1967. Influence of temperature on the rate of gastric juice secretion in the brown bullhead, Zctalurus nebulosus. Comp. Biochem. Physiol., 21: 125-132. Sokal, R.R. and Rohlf, F.J., 1969. Biometry - The Principles and Practice of Statistics in Biological Research. W.H. Freeman and Co., San Francisco, 776 pp. Starck, W.A.,II, and Davis, W.P., 1966. Night habits of fishes of Alligator Reef, Florida. Ichthyol. Aquarium J., 38: 313-356. Strickland, J.D.H. and Parsons, T.R., 1972. A practical handbook of seawater analysis. Fish. Res. Board Can., Bulletin 167 (2nd Edition), 310 pp. Teng Seng-Keh and Chua Thia-Eng (MS-a). Length-weight relationship and growth of young estuary grouper (Epinephelus tauuina Forsk%l) caught from the Middle Bank, Penang Straits. Teng Seng-Keh and Chua Thia-Eng (MS-b). Diurnal feeding activities of the estuary grouper (Epinephelus tauvina Forsk%l) in floating net-cages. Teng Seng-Keh and Chua Thia-Eng (MS-c). Effect of stocking density on the growth of estuary grouper (Epinephelus tauuina Forsk?d) cultured in floating net-cages. Vann, E, 1972. Fundamentals of Biostatistics. D.C. Heath and Co., London, 189 pp. Windell, J.T., 1966. Rate of digestion in the bluegill sunfish. Invest. Indiana Lakes Streams, 7: 185-214. Windell, J.T., 1967. Rate of digestion in fishes. In: S.D. Gerking (Editor), The Biological Basis of Freshwater Fish Production. Blackwell Scientific Publications, Oxford, pp. 151-173.