Species collection: A total of 200 pairs of mature healthy brood fishes were collected from the local market which were previously caught from Kopotakkha river and transported to Arabpur Fish Farm, Jessore where the experiment was conducted.
Induced breeding: Eight trial doses for female and three for male were used to find out the breeding performance with pituitary gland. The interval between first and second injection was 6 hrs for female but a single dose was administered to male during the first dose of female.
Female and male brood separation: The fishes were separated by sex and kept in plastic bucket after applying the required doses of PG. The plastic bucket was filled up to 25 cm, continuous tap water for each plastic bucket with nylon mesh windows at three sides to discharge water. A mesh net was placed on the top of the plastic bucket to prevent the escape of fishes by jumping until the females received their second dose of PG.
Hormonal extract preparation and injection: The acetone dried PGs were first placed on blotting paper so as to remove the excess acetone as much as possible followed by weighing with a sensitive scientific balance to pool the desired amount of PG. The pooled amount of PGs were finely crushed by tissue homogenizer and diluted with required amount (fish was injected with no more than 0.4 to 0.5 ml, to avoid injury) of distilled water. The solution was centrifuged to settle the tissue residue at the bottom and the resulting supernatant solution was then taken for injection with diabetic syringe. According to Rottmann et al. (1991), the concentration of hormone mixed in recommended dose, multiplied by the approximate weight of individual brood fish, was divided by the desired volume of the injection.
The volumes of injections were controlled at 0.1 to 0.2 ml for each parent fish. Various doses of PG were administered intramuscularly about 4 mm up from the lateral line longitudinal to the first spine of the dorsal fin. The second injection for female was administered at the opposite side of the first injection. In this regard, the fish was hold in one hand while administering the injection.
The volumes of injections were controlled at 0.1 to 0.2 ml for each parent fish. Various doses of PG were administered intramuscularly about 4 mm up from the lateral line longitudinal to the first spine of the dorsal fin. The second injection for female was administered at the opposite side of the first injection. In this regard, the fish was hold in one hand while administering the injection.
Determination of percentage and duration of different stages: Fertilization percentage of eggs collected from the leaves of date twigs were determined under compound microscope after 4 hrs of spawning. Hatching rate was calculated by the following: number of hatchlings/number of fertilized eggs x 100. Deformities rates were also estimated by eye observation. The experiment was designed in eight independent treatments and there were three replicates in each treatment.
Fry nursing: Nursery practices from yolk sac absorption to juvenile stages in tank nursery were done from 11 to 28 June, 2002. Physico-chemical parameters from the rectangular nursery tank were not measured because the exchange of water was done for several times.
Nursery tank preparation: Rotifer was cultured in (15 cm X 10 cm X 5 cm) rectangular tanks so as to meet the nursery requirement regularly. The selected tanks were thoroughly cleaned and filled with filtered freshwater for one feet and constantly aerated. The tanks were covered with closed mesh nets to avoid the interference of dragon fly and when necessary covered by white polythene especially during rainfall. The tanks were treated with mustard oil cake, triple super phosphate and urea at rate 75 mg l-1, 7 mg l-1, and 8 mg l -1, respectively. These fertilizers were kept in a container for 12 hr with water for conditioning and the resulting extracts were used as fertilizer every morning at 10 am. After fertilization, phytoplankters taken from pond water (by filtering with 60 µm mesh cloth dominated by Chlorella) was inoculated as a food for rotifer culture. However, application of fertilizer was stopped for certain days to avoid excess bloom of plankters. Seeds of rotifer were collected from pond water by filtering through a 150 µm mesh sieve and inoculate into the tank. The population of rotifer started to grow massively after three days of fertilizer application and the spawn was released into the tank just after 7 days of first manuring.