Abstract
Polyculture and monoculture of mola (Amblypharyngodon mola), punti (Puntius sophore), and chela (Chela cachius) with carps along with some aspects of their food, feeding habits and reproductive biology were carried out in the field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh from August 1996 to December 1998. To study the effect of mola on the production of carp, an experiment was conducted with two treatments. Three species of carp were stocked in treatmnet-1 while three species of carp along with mola were stocked in treatment-2. After four months of rearing, production of 1,479+79.13 and 1,274+78.70 kg/ha was obtained from treatments-1 and 2, respectively. Treatment to treatment variation in fish production was found to be significant (P<0.05), which indicated that mola exerted a negative effect on the production of carp. In the polyculture of carps with mola, punti and chela, carps were stocked at 7,500/ha and each of mola, punti and chela were stocked at 50,000/ha. A production of 1,863+10.50, 1,901+48.13, 2,128+68.70, 2,001+95.12 and 2,016+45.42 kg/ha was obtained in treatments-1, 2, 3, 4 and 5, respectively. The best production (2,128 kg) was given by treatment-3, where punti was stocked. It was also observed that if partial harvesting could be made, polyculture of Indian major carps with small fish was a better proposition in terms of biological production and economic return. While the monoculture of mola, punti and chela over a period of six months at a density of 100,000/ha gave a production of 805+25.94, 1,120+18.50 and 509+40.81 kg/ha, respectively. The production of punti was 39.13% higher than that of mola and 120% higher than that of chela. One hundred and twenty samples of each species of mola (Amblypharyngodon mola), punti (Puntius sophore) and chela (Chela cachius) were examined to determine their food and feeding habits. Mola and chela were found to be planktivorous and feed in the surface while, punti was an omnivore and feed in the water column. For the estimation of fecundity of mola (Amblyoharyngodon mola) punti (Puntius sophore) and chela (Chela cachius), 100 gravid females of each species were examined. The fecundity of mola, punti and chela were found to range from 1,023 to 6,803, from 3,267 to 30,288 and from 920 to 2,825, with mean number of 3,133+1,629, 9,431+6,790 and 2,140+7,56, respectively. The GSI values for female mola, punti and chela were found to range from 1.78±0.88 to 17.06±2.66, 1.16±0.36 to 24.81+1.50 and 1.34+0.64 to 10.19±2.17, respectively. The mean value of ova diameter was found to increase considerably in May and continued to increase up to October. Month wise variations in the histological structure of ovary indicate that mola, punti and chela spawned at least twice a year, once during May-July and again during September-October.