ABSTRACT
The experiment was conducted to evaluate the effect of stocking density on the growth and production performance of tilapia (Oreochron:is niloticus) in ponds. Three stocking densities were used as 150, 200 and 250 fish/decimal and designated as treatment T1, T2 and T3 respectively having three replicates. All the fishes were of same age group having body weight of 12.5 g. A formulated feed (28.25% protein) was applied @ 5% body weight, at the beginning of the experimental period and reduced to 3% of their body weight and continued up to harvesting period. The result of the present study showed that the fish in the treatment T1 resulted with the best individual weight gain (124.37g) followed by treatments T2 and T3 respectively. The specific growth rates (SGR) are 2.65, 2.60 and 2.36 and the food conversion ratio (FCR) values arel.82, 1.77 and 2.04 in treatment T1, T2 and T3 respectively. There was no significant (P<0.05) differences among the survival rate of fishes which ranged from 94.2 to 96.99%. The fish productions were 18.09, 22.76 and 21.74 kg/decimal in treatments T1, T2 and T3, respectively. But the highest production 22.76 kg/decimal was obtained from the treatment T2 with a stocking density of 200 fish /decimal.
Key words: FCR, Growth, Production, SGR, Stocking density and tilapia
INTRODUCTION
Modern fish culture means improvement of culture practices through adopting different measures such as proper doses of fertilizer application, regular feeding, optimum stocking density, maintenance of physicochemical factors, disease prevention and various control measures (Balarin and Hailer, 1982). The stocking density is the major concern for mono-culture. Some times excellent fish fry do not perform satisfactory growth unless correct stocking practices (Sanches et at 1999). In general the stocking density and growth of fish are very much related. The optimum stocking density ensures sustainable aquaculture providing proper utilization of feed, maximum production, sound environment and health. In comparison to low stocking density, high stocking density exerts many negative impacts such as competition for food and shelter and rapid out break of disease if occurred. Therefore it is important to optimize the stocking density for the target species in aquaculture for desired level of production. Tilapia has good resistance to poor water quality and disease, tolerance to a wide range of environmental conditions, ability to convert efficiently the organic and domestic waste into high quality protein, rapid growth rate and good flavour (Ballarin and Hallar, 1982). Tilapias are currently having important impacts on poor people in developing countries, both as cultured species in household-management systems and through access to fish produced in informal and formal fisheries (Edwards, 2003; and Little, 2003). But the culture practice of tilapia varies to a great extent from country to country and even among the different farming systems.
In view of above facts, the present experiment was undertaken to achieve the following objectives, to study the effect of stocking density on the growth and production performance of tilapia in ponds and determine the suitable stocking density for culture of tilapia in ponds.
MATERIALS AND METHOD
Study area
The experiment was carried out during the period from 151 March to 30th May, 2007 in ponds located at the South-West corner of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh.
Pond preparation ,
The pond dykes and embankments were raised and repaired properly in broken places and unwanted species was removed by-using rotenone @ 50 gm/decimal. After one week ponds were limed at a dose of 1 kg/decimal and fertilization of the pond was done with cow-dung, urea, and TSP (Triple Super Phosphate) @ 7 kg/decimal, 100gm/decimal and 100gm/decimal respectively.
Experimental design and stocking
The experiment was conducted in 9 mini ponds with three treatments in CRD i.e. T1, T2, and T3 each having three replications. The ponds were stocked with 150, 200 and 250 tilapia fingerlings per decimal in T1, T2 and T3.
Post stocking management
Fertilization
Fertilization of the ponds was done fortnightly with cow dung, urea and triple super phosphate (TSP). Cow dung was applied Q 3 kg/ decimal and urea and TSP fertilizers were applied @ 40 g /decimal. Urea and TSP were applied after dissolving them in water in a bucket and then spreaded over the pond surface manually.
Feeding
Throughout the experiment supplemental feed which contains 28.25% protein was given at the rate of 5% (151 month), 4% (2nd month) and 3% up to harvesting of their body weight. The feed was supplied in the dried form and feeding was done directly without any feeding trays. Half of the ration was supplied at 8.00 am and remaining half was supplied at 4.00 pm.
Water quality parameter monitoring
The four major water quality parameters such as water temperature, dissolved oxygen, transparency and pH were measured at 9 am by using a commercial kit box (Model: FF-3, USA) at monthly intervals.
Growth and production monitoring
The growth and production of fishes were measured monthly through random sampling method. The weight of fish (in gm) was measured by using a portable balance (Model: OHAUS) and were calculated by following formula.
Weight gain (g) = Mean final weight (g) -mean initial weight (g)
Mean final fish wt - Mean initial fish wt.
(%) Weight gain = _________________________________________ x 100
Mean initial fish wt.
).
Specific Growth Rate, (SGR% per day) = (Log, WZ -Log, W, ____ x 100
T, - Tz
Where, W1= the initial live body weight at time T1 W2= the final live body weight at time T2 Tz_ Ti = Duration of the experiment (day)
Food conversion ratio (FCR) = Feed fed (dry weight). x 100 Live weight gain Survival (%) = No-.of fish harvested.
x100
No. of fish stocked
Production = No of fish harvested x Final weight of fish Data analysis
Analysis of the data was done by using the software SPSS (Statistical Package for Social Science) version 11.5 significance was assigned at 0.05% level.
RESULTS AND DISCUSSION
Water quality parameters
The results of the water quality parameters such as temperature, pH, dissolved oxygen and transparency during the experimental period are presented in Tables 1 and Fig. 1.
Transparency
Water transparencies of the experimental ponds under different treatments are presented in Table 1.The mean values of transparency were 30.653.43, 31.751.08 and 35.7(5.6) for treatment T1, T2 and T3 respectively. There was no significant variation of transparency among different treatments. The present findings agreed with the findings of Kohinoor (2000) who recorded transparency values ranging from 15 to 58 cm. Wahab et al. (1994) found transparency ranging from 15 to 75 in polyculture pond. Rahman (1992) concluded that the transparency of productive water bodies should be 40 cm or less.
Water Temperature (°C)
During the study period, the water temperature varied from 26.65°C to 29.65°C in Tt , 26.60°C to 30.10°C in T2 and 26.65°C to 29.10°C in T3 (Table 1). The mean values of temperature in TI, T2 and T3 were 30.03 3.25, 28.623.52, and 27.533.20 respectively. Dewan et al. (1991) recorded the water temperature ranged from 29.3 to 34.OoC whereas Kohinoor (2000) observed the water temperature ranged from 24.2 to 33.30C. So the results of this study were similar to the findings of above authors.
Table 1. Average (Mean±SD) values of water quality parameters under different treatments throughout the study period
| Treatment | Water | temperature (°C) | Dissolved | oxygen | (mg/L) | | pH | Transparency (cm) | |
| Ti | 28.46.38 | 5.630. | 56 | 7.860.31 | 30.653.43 | ||||
| T2 | 28.62.52 | 5.710.51 | | 7.950.30 | 31.754.08 | ||||
| T3 | 27.53.50 | 5.160.74 | | 8.490.62 | 35.715.61 | ||||
Figures indicates mean values lstandard deviation
TI
T2
Treatments
T3
Fig I Average value of water quality parameters under
different treatments throughout the study period
different treatments throughout the study period
Dissolved Oxygen
During the study period, the dissolved oxygen contents of water were varied from 4.85 to 6.65 mg/L in T1, 5.10 to 6.65 mg/L in T2 and 4.35 to 6.65 in T3 (Table 1). The mean values of dissolved oxygen content obtained in treatments T1, T2 and T3 were 5.63 #3.56, 5.71, ± 0.51, 5.16, X1.74. Wahab et n1. (1995) recorded DO ranging form 2.2 to 7.1 mg/L in nine ponds of Bangladesh Agricultural University Campus, Mymensingh, while Kohinoor (2000) measured DO 2.0 to 7.9 mg/L in the seasonal ponds of BAU Campus, Iviy>nensingh.
. pH
The pH values under different treatments are presented in (Table 1). During the study period, the range of pH values recorded in treatment T1. Tz and T3 were found to vary between 7.35 to 8-05, 7.55 to 8.15 and 7.55 to 9.25 respectively. The mean values of pH obtained in the treatments T1, T2 and T3 were 7.86fl.31, 7.958.30 and 8.4937.62 respectively (Fig. 1). Hussain ( 1997) found pH 6.7 to 8.3, while Kohinoor et al. (1998) reported pH 7.2 to 7.3 in the research ponds of BAU Campus, Mymensingh.
Growth performance offish
For the evaluation of growth performance of fish in different treatments in terms of initial weight gain, specific growth rate (SGR% per day), food conversion ratio (FCR), survival rate (%) and production (kg/decimal/90 days) were calculated and are shown in Table 2. The present experiment showed the highest mean weight gain of fish in treatment Tl which was stocked at lower densities although same feed and feeding rate were applied in all the treatments.
Weight gain _
No significant (PO.05) variation was recorded in initial weight of fish under different treatments (Fig. 2). The mean weight gain of fish at the end of the experiment was significantly higher in Tl (124.375 g) than those of treatments Tz (118.6 g) and T3 (92.35 g). The mean lowest weight gain was obtained in T3 treatments which stoking rate was 250 fish/decimal. Kohinoor et al. (1998) obtained the highest growth of tilapia stocked at the rate of 80 fish/decimal fed with supplemental feed compared to those which received only fertilizer application.
160
--*--T1 -a--T2 -*-- T3
140 -
120 - 100
-
rn
o, 80 -
--y
3 so -
40 - 20 -
a
60
90
30 45
Days
Fig 2. Growth of tilapia into rms of increase in weight (g) in
diffarent treatments during the experimental period
diffarent treatments during the experimental period
75
0
15
Specific growth rate (SGR) and Food Conversion Ratio (FCR)
The mean specific growth rate of tilapia in different treatments ranged between 2.363 to 2.655. The significantly (P< 0.05) highest SGR values (2.65) was recorded in treatment Ti while the lowest (2.363) was obtained in T3. In the present study, the food conversion ratio was higher (2.04) in treatment T3 than T1 (1.82) and T2 (1.77) treatments.
Survival rate and production of fish
The survival as recorded in the present study was fairly high which ranged from 94.2 to 96.99% (Table 2). The survival rate recorded in present study is higher that the survival rate recorded by Hussain et al. (1987), which might be attributed to the relatively larger size of fingerlings (12.5 g) stocked in the present study. Although the mean weight gain in treatment T1 was the highest, the total yield of fish were highest in
treatment T2 followed by treatment Tl which is due to the higher stocking density i.e. the higher number of fish used in treatments T2 and T3 (Fig. 3). The present results supports the findings of Dirnitroy (1976) who achieved the best production from higher stocking densities (80 fish/m3) when compared to that achieved with the lower ones (15 and 50 fish/m3). Thus, the results of the present study indicated that a stocking density of 200 fish per decimal is optimum for tilapia culture in ponds.
Table 2. Growth parameters of tilapia observed in different Treatments
| Growth | | Treatment | |
| parameters | T1 | T2 | T3 |
| Mean initial weight (g) | 12.50-(@)) | 12.50 a (8) | 12.50 a (ffi) |
| Mean final weight (g) | 136.87a (8.17) | 131.10 b (8.56) | 104.85 r(fl.21) |
| Weight gain (g) | 124.37- (8.17) | 118.60 n (8.56) | 92.35 x(8.21) |
| Weight gain | 995.00 a (4.41) | 948.80 n (4.52) | 778.80 c (1.69) |
| SGR (% per day) | 2.65 a (01.0071) | 2.60 b (8.0071) | 2.36 c (8.0021) |
| FCR | 1.82 b (8.0085) | 1.77 1 (8.0148) | 2.04 a (8.0141) |
| Survival rate (%) | 96.99 a (8.47) | 96.00 a (8.70) | 94.20 a (8.84) |
| Fish production (kg/decimal/90 days) | 18.09 b (8.11) | 22.76 x(8.28) | 21.74 x(8.14) |
*Values in the same row having the same superscript are not significantly different (P<0.05), values are given with t standard deviation
CONCLUSIONS'
By concluding the conducted study the effect of stocking density on the growth and production .performance of Tilapia in ponds fed with formulated diet for a period of three months in nine experimental ponds, the different issues related to experiment i.e. the water quality parameters such as temperature, dissolved oxygen, pH and transparency and growth performance of fish in different treatments in terms of initial weight gain , specific growth rate (SGR% per day), food conversion ratio (FCR), survival rate (%) and production (kg/decimal/90 days) were calculated, analyzed and discussed. From the experiment it may be suggested that the optimum stocking density (200 fish/decimal) performs the better results.
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