2.1 Pond selection and preparation The experiment was carried out for a period of two months from 14 March to 18 May 2015 to evaluate the effects of stocking density on growth and production of monosex male tilapia in nine experimental ponds situated in the Field Laboratory Complex, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh. The area of each pond was 2 decimal with an average depth of 1.2 m all ponds were rectangular in shape possessed similar size, basin confirmation and bottom type. Prior to stocking, ponds were dried and cleaned for weeds and unwanted aquatic animals. The dried ponds were left exposed to sunlight for several days and then limed at the rate of 250 kg/ha. Five days after liming, ponds were filled-up with deep tube well water up to the depth of 1 meter. After three days, ponds were fertilized with cowdung at the rate of 1,000 kg/ha.
2.2 Experimental design The ponds were selected randomly to accumulate the relevant treatments.
2.3 Collection of fries The monosex male tilapia fries (O. niloticus) were collected from the Reliance Hatchery, Shikarikanda, Mymensingh and transported to the farm in oxygen filled polythene bags covered by jute bags. After acclimatization the fries were transferred to culture ponds. During stocking sufficient care was taken in respect to physico-chemical condition.
2.4 Fish stocking Fries of monosex male tilapia (O. niloticus) were stocked in 20 March 2015 according to the experimental design. All ponds of various sizes were divided into three groups viz. group-1, group-2 and group-3. The ponds belongs to group-1, group-2 and group-3 were stocked with monosex male tilapia fries at the stocking density of 12,500 (T1), 25,000 (T2) and 75,000/ha (T3), respectively.
2.5 Feeding strategy At the beginning of the experiment feed was supplied at the rate of 30% of the body weight of reared monosex male tilapia and gradually it was readjusted to 25%, 20%, 15%, 14%, 13%, 12% and 10%, respectively. 2.6 Water sampling and analysis Water quality parameters such as water temperature, transparency, pH, dissolved oxygen (DO) and total alkalinity were determined at weekly interval between 0900 to 1000 hrs. Temperature was recorded using a Celsius thermometer, dissolve oxygen was measured by a portable digital DO meter (Jenco 9713) and pH was measured by pH meter (Hanna pH 300).
2.7 Analysis of experimental data on growth performances Experimental data was collected during the growth trial were used to determine mean weight gain (g), average daily weight gain (g), specific growth rate (%/day) and survival rate (%).
2.8 Production (kg/dec/2 months) At the end of the experiments, most of the fishes were caught by net and the rest by draining out the ponds. It was calculated as: Production = No. of fish harvested × Average final weight of fish (g).
2.9 Statistical analysis The data obtained on the growth performance of fish, survival rate and production were statistically analyzed to see whether the influence of different treatments (stocking densities) on these parameters were significant or not. One way analysis of variance (ANOVA) was done with the help of SPSS (Statistical Package for the Social Sciences).