In many fish ponds, blue-green algae (Cyanobacteria) constitute the greater part of the phytoplankton. Of the blue-green algae common in fish ponds, Microcystis aeruginosa is said to be a noxious species. Itsometimes forms spectacular water blooms, often with harmful consequences such as depletion of oxygen, poor growth of fish and even mass mortality among the fish. The present study was aimed atinvestigating the influence of different levels of M. aeruginosa on the water quality and fish production of carp culture ponds. For the present study, three carp culture ponds with high, moderate and low levels ofM. aeruginosa were selected. In the three ponds, physico-chemical parameters of water, phyto- and zooplankton and fish production were studied. The results indicated that the fish yield was low withconcomitant fish mortalities in the pond with high levels of M. aeruginosa compared to the other two ponds. The influence of the different levels of M. aeruginosa on other planktonic groups and in turn their effect on fish production were analyzed and discussed in the light of the existing literature
