Effects of fry stocking densities on growth, survival rate and production of Hypophthalmichthys molitrix, Cyprinus carpio var. specularis and Labeo rohita in earthen ponds at Natore fish farm, Natore, Bangladesh

The experiment was conducted to determine the effects of fish population density on the growth and production of carps fries (Silver carp, Mirror carp and Rui) in polyculture for a period of 90 days in earthen ponds. Mean individual stocking weight (wt) (g) of the fry of silver carp, mirror carp and rui were 0.10, 0.103 and 0.08 under treatment-I and were 0.17, 0.142 and 0.11 under treatment-II. In the ponds under both treatments, inorganic and supplementary balanced feed (50% per body weight) was used to the cultured ponds for spawn to fish fingerlings. During the experimental period, the ranges of water temperature (26 to 34 0 C), transparency (28 to 41 cm), dissolved oxygen (2.45 to 5.5 mg/L), pH (7.0 to 8.5), total alkalinity (130 to 182 mg/L), and ammonia nitrogen (0.12 to 0.3 mg/L) found were within the productive limit and more or less similar in all the ponds under treatment-I and II. The survival rate of silver carp was 38.60 and 66.48 under treatments I and II. The survival rate of mirror carp was 31.20% and 45.50% under treatment I and II and the survival rate of rui was 31.51% and 53.35% under treatment I and II, respectively. The calculated net fish production of the ponds under treatment-I was 1905.13±141.95 kg ha -1 90d -1 and that of the ponds under treatment-II was 3831.74±411.35 kg ha -1 90d -1 . It was found that net fish growth, survival rate and productions was better in treatment-II than treatmentI. Finally it is concluded that the growth, survival rate and production of fry up to fingerlings would be better by intervention of proper stocking density of various fish species in pond fish culture.