Abstract
Cultures of the blue green algae (cyanobacteria)Anabaena wisconsinense andOscillatoria curviceps were isolated from fish farms and their antimicrobial effects were studied. Solvent extracts of exponential phase algae were screened for antimicrobial activity against different species of Gram positive (Lactobacillus sp. andBacillus firmus) and Gram negative (Aeromonas hydrophila, Pseudomonas fluorescens andPseudomonas anguilliseptica) bacteria and the fungi (Aspergillus niger andSaprolegnia parasitica) which were all isolated from diseased fish. Maximum antimicrobial activity was observed with ethanolic extract ofO. curviceps againstLactobacillus sp. andAeromonas hydrophilia, whereas, methanol extracts ofA. wisconsinense andO. curviceps had antibacterial effects againstB. firmus, A. hydrophila, P. fluorescens, P. anguilliseptica, and the fungiA. niger andS. parasitica. It was also observed that solvent extracts ofA. wisconsinense when injected intoOreochromis niloticus which was already injected intraperitoneally with 2 × 106 CFU/mlP. anguilliseptica significantly decreased fish mortality from 50 to 12.5%.
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