POLYCULTURE OF CARPS WITH SMALL INDIGENOUS SPECIES (SIS) MOLA (Amblypharyngodon mola) AT GAZIPUR AREA OF BANGLADESH

Abstract

An experiment was carried out to evaluate the impact of pond sizes on the production potential of mola, Amblypharyngodon mola with carps for a period of 5 months from mid August 2003 to mid January 2004 at Sreepur Upazila in Gazipur district. Fifteen ponds were divided into three treatments each with five replicates. Rohu (Labeo rohita), catla iCatla catla), mrigal iCirrhinus cirrhosusi and exotic silver carp iHypophthalnnchthys molitrix) were stocked at the stocking densities of 10,0001ha at the ratio of I :0.5:0.5: I, while small indigenous fish mola (Amblypharyngodon mo/a) were stocked at 25,0001ha and grass carp (Ctenopharyngodon ide/la) was stocked at 5001ha. Major carps and mola were common in all treatments. All ponds were subjected to same regime of feeding and fertilization. The commonly available agricultural byproduct rice bran (100%) was used once per day as supplementary feed at the rate of 3% body weight of standing crop of fish. Soft grasses and banana leaves were supplied for grass carp on daily basis up to satiation. All ponds were fertilized with manure (cow dung) at the rate of 1,000 kg/ha at fortnightly intervals. All feeds and fertilizer inputs were supplied from farmers' households. Various water quality parameters such as water temperature, transparency, dissolved oxygen, pH, alkalinity and chlorophyll-a were monitored at monthly interval and found almost similar in three treatments. The mean values of various water quality parameters were within the suitable ranges for freshwater aquaculture in Bangladesh. The survival rates of carp species were fairly high and ranged from 79.63 to 91.67%. The production of carps and small fish were together 2,413.25, 2,492.94 and 2,346.66 kg/ha in treatments 1,2 and 3, respectively, which were not significantly different. The overall best production was obtained in Treatment 2 where the pond size was 10-20 decimal. It was observed that if partial harvesting is made, polyculture of major carps with small fish, mol a is a better proposition in terms of biological, nutritional and economic point of view. The farmers can keep the small fish for their family consumption and can sell the large carps as cash crop.