The data used in the present study were collected from a semi-intensive culture farm, "Gazi Fish Culture Ltd" Dakope, Khulna. It is a Shrimp Culture Project of SABINCO (Saudi Bangladesh Industrial and Agriculture Investment Company Ltd.), Bangladesh. The culture was conducted for 110 days from July 20 to November 10, 2007.
Experimental ponds: Out of eighty grow out ponds of the farm, six ponds were selected (for three treatments with two replicates) for the present study. Each pond was 4000 m2 in size. Three salinity levels such as, 10 ppt, 7 ppt and 5 ppt for the treatments T1, T2 and T3 respectively with two replicates were maintained in the experiments. All the ponds were prepared following same procedure. Each pond was equipped with 2 inlets, 2outlets and 2 paddle wheels for exchanging and maintaining water quality. The water depth was maintained at 1.1-1.2 m throughout the culture period. Shrimp fry of 5g mean body weight were collected from the hatchery of Gazi Fish Culture Ltd. After 40 days of rearing, the juvenile shrimp were released into the grow out ponds with the same density of 4 individuals m-2. A commercial pelleted feed, CP Feed was used to feed the stock
Estimation of growth, survival and production: Sampling of shrimp weight was carried at 14 days intervals by using cast net. Feeding tray was used to monitor shrimp health and growth. The shrimp from each sample were weighed individually to estimate the growth. After 110 days of culture survival, body weight and production was estimated through complete harvesting by draining out the pond water. Calculations for estimating survival, average body weight and production per hectare were done for each treatment separately. The growth rate (GR) was calculated by using following formula of Bagnal (1978).
Growth Rate (GR) = Weight (g) gained on nth days/ Total culture days (up to nth day)
Where, “n” represent the shrimp age
Calculation for economics: The economic analysis was done on the basis of production costs and sales value of the crop and the economic return among the different treatments were compared. Juvenile: The juvenile shrimp was bought at a price of tk. 2500 per thousand. Feed: The price of feed used (CP shrimp feed) varies with the types of feed (starter - finisher). The costs of feed were calculated for different treatments separately. Labour: Generally, single culture cycle per year is practiced in the culture ponds. Yearly salary for pond associated personnel was calculated to estimate the costs for labour for the production per hectare per year.
Power: Power costs include costs for pumping, aeration and lighting. The total costs for fuel used in generators and running pumps during the culture period were recorded. The power cost for production per hectare was estimated. Value of the crop: At harvest, the selling price for the heads-on shrimp was determined based on the offered price for each grade of the harvested shrimp. The recognized grades and the price offered for each grade are presented in Table 1
Estimation of economic return: The economic return was estimated by subtracting the production cost/ha from the value of the produced shrimp/ha in different treatments. Percentage of economic return in different treatments also has been calculated by using the following formula.
Economic return ha-1= (Crop value ha-1) – (Production cost ha-1)
% of Economic Return = (Economic return ha-1/Production cost) × 100