Brood fish collection: Mature males (10 pairs) and females (20 pairs) having an average weight of 1.5 kg and 1.65 kg respectively were collected from Bangladesh Fisheries Research Institute, Mymensingh and reared in an earthen pond. The brood fish were provided with a supplementary diet composed of fishmeal (20%), mustard oil cake (20%), sesame oil cake (12%), soybean oil cake (12%), wheat bran (15%), rice bran (15%), wheat flour (5%), and vitamin premix (1%) (Mollah, 2001). The supplemental feed was administered twice a day (at 9.00 and 16.00 h) at the rate of 3-5% of their body weight, which enhances the gonadal maturation in fishes.
Breeding and spawn collection: Five pairs of ready-to-spawn male and ten pairs of female common carp were collected from the stocking pond and kept in a hapa (152.4 x 106.7 x 121.9 cm3) with water hyacinth for spawning. The fertilized eggs were collected from hapa and incubated in a cistern having aeration facilities from the porous plastic pipe for a period of 72 hours. Hatching was started after 58 hours of incubation and completed within 72 hours. After absorption of egg yolk, the hatchlings were collected from the cistern and transferred into the rectangular size tray (96.52 x 36.83 x 10.16 cm3) and reared up to three days. Then the spawn was fed with boiled chicken egg yolk.
Experimental setup The feeding experiment was divided into two phases; the first one was done in the Wet laboratory of Fisheries Faculty, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh for a period of 35 days. Three days old spawns of common carp were stocked in a plastic bowl having a water holding capacity of 10 liter and continuous flow of water from porous pipe and outlet facilities. The experiment was designed with 4 treatments (T1, T2, T3 and T4) .and each treatment contained 3 replications. Each replicate bowl contained 200 larvae (average length 5.45±0.25 mm and weight 5.31±1.029 mg) at a stocking density of 20 larvae/L of water. The feed was formulated according to the different amounts of 17 a-methyl testosterone hormone. At the first defined amount of 17 a-methyl testosterone were dissolved in 250 ml ethanol and then were mixed with per kg nursery feed Starter-I (SABINCo).
The second trial was performed with the same larvae (35 days hormone-treated common carp) reared for another 90 days in four experimental hapa (152.4 x 106.7 x 121.9 cm3) that were placed in a pond of Field Complex, Faculty of Fisheries, Bangladesh Agricultural University (BAU), Mymensingh. During the rearing of post-hormone treated fry, they were fed a nursery feed (starter-Ill) at the rate of 8-12% of their biomass. The feed contained 92.21% dry matter, 23.39% protein, 11.49% lipid, 8.72% crude fibre, 29.98% NFE and 20.42% ash.
Rearing of larvae The water of each bowl was exchanged by half of the volume with fresh deep tube-well water twice a day. The fecal output and waste of feed were removed from the bowl by siphoning twice a day. The feed was provided at the rate of approximately 8-12% body weight twice a day (at 9.00 and 16.00 h). The physicochemical parameters such as dissolved oxygen (DO), free carbon dioxide (CO2), total alkalinity (carbonate and bicarbonate), pH and temperature were estimated weekly in each bowl.
Sex identification Sex of fish was determined by examining the gonads. The fish was dissected and the gonad was stained with an aceto-carmine solution and then squashed with gentle pressure on the slide to observe their sex with a light microscope. Fish with recognizable ovarian and testicular portions were classified as female and male respectively. Fish with filiform (thread lik9) gonads were classified as sterile.
Analytical method The Physico-chemical parameters such as temperature, pH, dissolved oxygen (DO) and ammoniacal nitrogen were estimated weekly in each aquarium with the help of Aqua mate water testing kit (Model WAQ-IA). The proximate composition of the feed ingredients was analyzed by standard methods (AOAC, 1980). The fish were sampled at weekly intervals to determine the change in their growth (length and weight). Sampling was done in the early morning when the fish stomach was empty. The specific growth rate (SGR) was calculated as the percentage increase in body weight per day over a given time interval by the following equation:
Specific growth rate = (LnW2 - LnWI) / (T2 — T1) x 100 where, W2 = final live body weight (g) at time T2 W1 = initial live body weight (g) at time T1
Data analysis: The length gain (mm), weight gain (g), percent length gain, percent weight gain and specific growth rate and survival rate of larvae were tested using one-way analysis of variance (ANOVA). Significant results (P<0.05) were further tested using Duncan's. New Multiple Range Test (DMRT) to identify significant differences among means. This statistical analysis was performed with the aid of the computer software MSTAC program.