ABUNDANCE AND SPECIES COMPOSITION OF THE FISHES IN BLUE NILE RIVER BELOW THE TISS ISSAT FALL, ETHIOPIA

Abstract

In the present study we evaluate the relative abundance and species composition of fishes in Blue Nile River below the fall during the wet season (September-October 2010) and dry season (March-April 2011). Fish samples were collected by using monofilaments gillnets (5-55 mm) and multifilament gillnets, having mesh sizes of six, eight, ten, twelve and fourteen centimeter stretched bar mesh, having a length of twenty five meter and depth of one and half meter, on three sampling sites of the Blue Nile River below Tisisat Fall. Eight hundred fifty seven fish specimens that belong to a single class, Actinopeterygii (ray-finned fishes), four orders, and five families and 6 genera were collected. The most dominant species were Labeobarbus intermedius, Labeo forskalii and Mormyrus kannume. The site harbors large flock of L. intermedius population. Sefiana site had the higher diversity (average H'=3.02). Labeobarbus intermedius was the most dominant (39.67% by number) followed by Labeo forskalii (27.77%) and M. kannume (11.67%). The other species, L. nedgia, B. docmak, L. crassibarbis, C. gariepinus and O. niloticus were found in 9.57%, 5.13%, 3.50%, 1.98% and 0.70%, respectively. All fish species except C. gariepinus and O. niloticus were found in all sites. All the fish species except L. crassibarbis, B. docmak and C. gariepinus showed significant differences in abundance between seasons with overall catch composition of 39.67%, 27.77%, 9.57%, and 11.67% for L. intermedius, L .forskalii, L. nedgia and M. kannume, respectively. L. intermedius, L. forskalii, L. nedgia and M. kannume were the most important species in both seasons and in most of the sampling sites. The studied habitats are in danger being eroded and therefore catchment rehabilitation should be considered and the massive seasonal fishing by the local communities should be reduced