Abstract
Both qualitative and quantitative fluctuations of different group and species of plankton and benthos during the two years period from November 1978 until October 1980 were studied. Twenty seven species of phytoplankton, thirty two species of zooplankton and twenty five species of benthos were recorded and their mean, standard error and relative percent abundance were calculated. Some group and species were numerically more important than the others. Month and depthwise abundance of phytoplankton differed significantly during the first year but during the second year, only the monthwise abundance of phytoplankton differed significantly. The intra-species variations of phytoplankton were observed during both the years. The different group and species of phytoplankton, zooplankton and benthos generally had their peak of abundance in different months. The combined effect of various group and species of phytoplankton, zooplankton and benthos was observed on the growth and abundance of another and some significant results were recorded during both the years. The rainfall, total hours of sunshine, pH, temperature and transparency of water had significant combined effect upon the abundance and growth of various species of phytoplankton, zooplankton and benthos, specially during the first year. During both the years, various species and group of phytoplankton, zooplank- ton and benthos were directly or inversely correlated with one another. Again, phytoplankton, zooplankton and benthos as groups were either directly or inversely correlated with one an- other during both the years.
During the study of food and feeding habits of Labeo rohita, 120 fishes were examined but none of the fish was found with empty stomachs. The average indices of fullness of the stomachs were the highest in February and March in the first year and September in second year. The fish was found to feed on a variety of food items and the main food categories recorded were Myxophyceae, Chlorophyceae, Bacillariophyceae, Debris, Rotifers, Cladocera and Copepoda. Although the fish was omnivorous, plant food contributed to the bulk of the food.
The stomach contents of 120 specimen of Catla catla were examined but none of the guts were found to be empty. The average index of fullness of the stomachs was the highest in September in the first year and February and March in second year. Although the fish was found to feed on variety of food items, it showed preference for animal food group.
During the study of food and feeding habits of C. mrigala the stomach contents of 120 fishes were examined and no gut was found empty. The average indices of fullness of the guts were the highest in November in first year and December and January in the second year. Plants appeared to be the most preferred food for this species although a small amount of animal food was contributed from animal food. Presence of sand and mud in the gut contents indicated that it was a bottom feeder.