Abstract
Feeding and breeding biology and some population parameters of Gudusia chapra (Hamilton, 1822) locally called chapila in Rajdhala beel (24°70' to 25°80' N and 90°29' to 90°48' E), Purbadhala. Netrakona, Bangladesh were studied during January 2003 to December 2004. Among the different small fish species of Rajdhala beel G. chapra contributed about 23% to the total catch in 1996-97. The annual fish production of the beel has been reported to show a gradual decreasing trend, about 13.4 tons in 1997-1998. 8.4 tons in 1998-1999 and 5.9 tons in 2002-2003, and this reduction was found to be mainly due to reduction in G. chapra catch. In this context, it was felt desirable to explore the specific causes of stock depletion in order to maintain sustainable stock and catch of G. chapra in the beel. Results showed that the physico-chemical characteristics of Rajdhala beel were found to be congenial for fish life. Thirty-eight genera of phytoplankton under five major groups and thirteen genera of zooplankton belonging to two major groups were recorded from the beel. The gut content analysis revealed that G. chapra is a plankton feeder, consumed chlorophytes (51.02%), cyanophytes (37.01%), bacillariophytes (6.2%), dinophytes (1.33%). crustaceans (3.03%), and rotifers (1.41%). The Gonadosomatic index and histological study of gonad revealed that G. chapra spawned during February to August, but the peak spawning was in March while a second minor peak was in July. The fecundity was found to range from 32.798 to 1.80,329 with a mean of 1,13,465±19,876. The mean K, value was found to be 1.09 in 2003 and 0.99 in 2004 indicating that the fish were in good condition. The growth of G. chapra in the beel was isometric in the first year and towards allometric in the second year of the study period. Analysis of length- frequency data using FISAT computer software package indicated that the fish recruited twice in a year and the present fishing pressure has exceeded the optimum level. Participatory Rural Appraisal (PRA) analysis showed decline in biodiversity of different small indigenous species (SIS) of fishes. The declining trend of annual G. chapra production is possibly due to over fishing (24%) of chapila and stocking of fingerlings of major carps like silver carp (Hypophthalmichthys molitrix) and catla (Catla catla) has led to food competition by the stocked majc. carps having similar food and feeding habits. Use of chemical fertilizers, pesticides and insecticides in the nearby agricultural land may also have some effect on declining biodiversity of fish in the beel. It was observed that the beel fishery as a whole and chopila in particular play a pivotal role in various ways in the family nutrition and livelihood of the rural poor community living around the beel.