Bloom Forming Cyanobacteria: A Threat to Aquaculture Practice in India

Abstract

In recent years, due to increase in eutrophication of water bodies, which involves enrichment of plant nutrients, specially phosphorus components, there has been a major shift in phytoplankton community leading towards 'bloom forming' toxic cyanobacteria. These species are capable of producing potentially lethal toxins and have been implicated in numerous instances of fish kills and deaths of domestic livestock. In Darbhanga, three such cases were recorded. Studies revealed a thick cyanobacterial bloom dominated by Microcystis aeruguinosa (7.6 x 10 units/ml) and Anabaena. Other toxic cyanobacterial genera included Nostoc, Oscillatoria, Gleotrichia and Aphanizomenon. Bioassay test was conducted on Channa punctatus. The aliquot was prepared from the cellular sediments collected from thick bloom situation of the respective ponds by lysing the cell walls. All the fish died within 18 hours indicating the sample to be positive. In moribund fish, the symptoms characterising neurotoxic effects of algal poisoning were well marked. In India, the literature, of late, suggests that the physical and chemical qualities of inland water is rapidly changing towards eutrophication due to pollution. As a consequence frequency of the 'toxic-algalblooms' can be expected to increase posing a threat to aquaculture practices.