Abstract

As microalgal blooms are very common and making serious problems in water bodies throughout Bangladesh, an investigation was carried out to see the composition and succession of noxious blue-green algae in pangasiid catfish (Pangasianodon hypophthalmus) ponds. During the course of the study, 20 species of Cyanophyceae were recorded, and among them Microcystis aeruginosa was the most abundant compared to other species. Significant occurrence of Microcystis viridis was also observed. Efforts were made to study certain physico-chemical factors and their influence on the composition and seasonal abundance of these species. Peak abundance of M. aeruginosa was observed from July to August. Moderately higher water temperature, lower rainfall and NO₃-PO₄ enrichment increased the biomass of both M. aeruginosa (168.72×10³cells/L) and M. viridis (8×10³cells/L) in the experimental ponds. Higher feeding rate in monoculture of pangasiid catfish (P. hypophthalmus) made the ponds hyper nutrified by unutilized feed and fish excreta that supported the higher abundance of these Cyanophyceae. In composite culture ponds, silver carp (Hypophthalmichthys molitrix) effectively grazed down the microalgae and as a result, algal bloom was not noticed.

Keywords

algal bloom, cyanophyceae, Microcystis aeruginosa, Microcystis viridis, pangasiid catfish