Abstract
Bangladesh. The study was conducted to determine the natural reproductive success of major carp in Kaptai Lake. The study was carried out at the four previously identified natural breeding grounds of Kaptai Lake from 2016 to 2018. Based on observed values of Gonadosomatic Index (GSI) of major carp species, it can be regarded that May and June are the peak breeding season in each year. Post-nursing period survey results indicated that fingerlings of different carps (Rui, Catla, Mrigal, Calibaush, Bata) are present in the breeding and nursing grounds. Among the identified species, 28% Rui, 12% Catla, 29% Mrigal, 8% Kalibaush, and 23% Bata. In the present study, investigations were made on a few physical and chemical factors of the water in the breeding grounds of the lake. The recorded values of air and water temperature, pH, water depth, and transparency did not change significantly among the sampling areas (P>0.05). Dissolved oxygen (DO) was found higher in the Chengi channel, followed by Rainkhiang, Kasalong, and Barkal channels. Also, higher free CO2 concentration was found in the Chengi and Rainkhiang channels than in Kasalong and Barkal. The total alkalinity was found higher in the Chengi and Rainkhiang channels, followed by Kasalong and Barkal. The contribution of total hardness was also exhibited higher in the Barkal channel than in those of Chengi, Rainkhiang, and Kasalong. Among Phytoplankton and Zooplankton, the dominant orders were Chlorophyceae and Rotifers, respectively. The highest rainfall in the lake area was found in June and July, which has a direct impact on the natural breeding of carps in Kaptai Lake.