Abstract
The ecology of 20 species of fishes belonging to 10 fami- lies has been investigated in a 7.5-acre artificial and perennial lake located on the campus of the Bangladesh Agri- cultural University, Mymensingh.
The physical environment of the fishes was studied with respect to the size of the habitat, source of water supply, depth of water, transparency of water, seasonal and diel changes in the temperature of air and water, and also the colour of water. The maximum and minimum depths of water in the lake were 261.5 cm and 109.3 cm respectively. The trans- parency of water showed correlation with the volume of water. No thermal stratification was detected in the lake. The colour of water was grey to brownish green.
The chemical environment of the fishes was studied with respect to seasonal and diel changes in dissolved oxygen, free CO2, ph and alkalinity of the water, and to pH, phosphorus, nitrogen, calcium and potassium of the bottom soil. The dissol- ved oxygen content of water was inversely related with tempera- ture. Free CO2 and dissolved oxygen held an inverse relation- ship in the water. Direct relationships between phi and total alkalinity, and dissolved oxygen and total alkalinity, and inverse relationship between free CO2 and carbonate alkalinity were observed in the lake. The changes in dissolved oxygen, free CO2, pli and alkalinity contents observed in the water column indicate that the lake was fairly productive. The phi, available phosphorus, total calcium and available potassium in the bottom soil indicate that the lake was fairly productive. The lake was, however, poor in available nitrogen.
The biological environment of the fishes was studied with respect to aquatic macroflora, phyto- and zoo-plankton, peri- phyton and benthos. Twenty six species of aquatic macrophytes belonging to 22 genera and 12 families were recorded from the lake. Their seasonal dynamics were determined. These plants provided food, shelter and breeding sites to the fishes.
Forty six genera of phytoplankton belonging to Chlorophyceae (22 genera), Bacillariophyceae (12 genera), Euglenophyceae (5 genera), and Myxophyceae (7 genera); and seven groups of zoo- plankton belonging to Protozoa (3 genera), Rotifera (12 genera), Cladocera (6 genera), Cope poda (3 genera), Ostracoda, Hydra carinae and Insecta were detected in the lake. Eugleno- phyceae and Chlorophyceae were the most dominant groups of phytoplankton. They showed summer and winter maxima. Rotifera was the most abundant and dominant group of zooplankton. Zooplankton did not show any seasonal rhythms. The density of zooplankton populations was higher than phytoplankton populations in the lake. They played significant role in the food chain of fishes. The seasonal dynamics of both phytoplank- ton and zooplankton have been determined.