Experimental Fry Collection: The fry of leather carp (C. carpio var. nudus) were collected from Chanchra of Jessore district and transferred to the Fish Physiology and Breeding Laboratory of FMRT Discipline, Khulna University with the oxygenated bag. The fry was then kept in the hapa at the university pond for a few days.
Acclimatization: The species were brought into the laboratory from hapa and then given prophylactic treatment with both in 0.5 ppm KMnO4 solution. Before starting the experiment, the fish were acclimatized to the experimental system for one week. During this period, the fish were fed with formulated pelleted feed containing 25% protein (prepared in the fish nutrition laboratory).
Feed Formulation Ingredient selection: Feed ingredients that were used in the experiment were a fish meal, rice bran, wheat bran, wheat flour, and mustard oil cake collected from the local market. Ingredient analysis: The collected ingredients were analyzed to evaluate the protein ratio (%). Proximate composition (protein, lipid and moisture) of the prepared feed were analyzed according to AOAC (1980). Protein was determined by Kjeldahl and Soxhlet apparatus. Protein level was maintained according to the Pearson square method (Pearson, 1976). Five types of diet were prepared by adjusting these ingredients in such a way to obtain 25%, 30%, 35%, 40% and 45% protein and treated as T1, T2, T3, T4 and T5, respectively. Pegabind, a synthetic binder, was used as a binder of fish feed while fish meal and oil cake were used as basal ingredients. Thereafter, water was added to the mixture in such an amount that the feed was in semi-moist form. An electrical extruder pellet machine was used to make the feed pelleted and dried in sun and preserved in the deep freeze.
Experimental Procedure: The experiment was conducted for seven weeks in the Fish Physiology and Breeding Laboratory of FMRT Discipline, Khulna a University. Collected fry was reared in aquaria (50x30x30cm3) containing 15 liters of water at a stocking density of 15 fry/aquarium. Each treatment was conducted with two replications. The average initial weight and length of fry were 2.62 ± 0.02 g and 4.32 ± 0.04 cm, respectively. The fry was fed twice daily between 9.00 am to 7.00 pm at the rate of 5% of their body weight. About two-third of the water from each aquarium was partially replaced with clean water every day before feeding. Proper aeration was done to supply sufficient oxygen into the aquaria and it was continued till the completion of the research. The feces in each aquarium were removed by siphoning and the dead fry (if any) were removed and counted in the morning and in the evening prior to each feeding. Adhered dirt inside the aquarium walls was cleaned twice a week. Weekly sampling was done for length and weight.
Water Quality -Parameters: Water quality parameters such as temperature, dissolved oxygen (DO), pH were recorded daily throughout the experimental period, but the result is presented in a weekly basis. The temperature and DO of each tank were recorded by a centigrade thermometer and DO meter (Lutron DO5510), respectively. The pH was determined with the help of a pH meter (Hanna, ISO 9001). The alkalinity of the water sample was determined with the neutralization titration method and total alkalinity was calculated by the following equation:
Biological Data Collection Dead fish was counted daily when noticed. Measurement of weight and total length of more than seventy-five percent fry from each aquarium was taken every seven days interval. Electric balance (B303-S, Mettler Toledo) was used to determine the weight in g. A measuring scale was used to determine the length at cm level. Weight gain, length gain, specific growth rate, survival rate and feed conversion ratio were determined according to the following formula:
a) Growth Rate (g/day) = W 2 -W1 / T2 -T1
Where, W2 = Weight (g) at time T2 WI = Weight (g) at time T 1 T 2 = Date of last sampling T 1 = Date of previous sampling.
b) Weight gain (g) = Mean final weight -mean initial weight.
c) Length gain (cm) = mean final length - mean initial length
d) Specific Growth rate (%) = In final weight (g)- In initial weight (g) / Time (days) x 100
e) Feed Conversion Ratio (FCR) = Dry weight of feed / Wet weight gain
f) Survival rate (%) = Number of live fish / Total number stocked fish x 100