Fusarium - A new threat to fish population in reservoirs of Kumaun, India

Fusarium moniliforme and F. udum (Moniliales: Deuteromycetes) were found to be natural pathogens of freshwater fish in reservoirs, causing mycosis and high mortality in Barbus rana, Channa punctatus, Labeo rohita, Mastaceambl us armatus, Mystus tengra, Puntius sophore and Wallago attu. Both the speci es produced clinical symptoms similar to natural infection in C. punctatus and P. sophore and caused 40-80% mortality under artificial inoculation, Th ough 9 other species of extra aquatic fungi belonging to 8 genera of hyphom ycetes were also associated with the diseased fish in the reservoir, they w ere unable to infect the test fish. Fusarium species parasitize fish more c ommonly during summer through rainy season. A temperature above 25 degrees C, coupled with relatively low pH (7.1-7.7) and DO (8.3-9.5 mg l(-1)) encou raged association and infection of these fungi, whereas low temperature dur ing winter (<20 degrees C) adversely affected their colonization on the fis h. Notably mycosis due to watermolds is prevalent during winter-spring, whi le extra-aquatic fungi dominate during summer through the rainy season, thu s posing a continual threat to fish in the reservoirs. This necessitates an integrated approach to combat mycosis in reservoirs. Besides, prophylatic measures to protect fingerlings before being introduced into the reservoirs , intensive research on biological control of fish diseases caused by Fusar ium and other fungal species is warranted, not only to increase production in reservoirs but also to conserve several rare fish species.