Assessment of Zooplankton Community Structure of the Bahir Dar Gulf of Lake

The zooplankton composition of the Bahir Dar gulf of Lake Tana was studied in June and July, 2007. A total of forty four zooplankton species made up of 16 species of rotifers, 16 species of cladocerans and 12 species of copepods and their developing stages were recorded in the following order of dominance; Rotifera> Cladocera> Cylopoida> Calanoida. The number of species was not too different among the three sampling Stations, however, average zooplankton abundance, was significantly higher (P<0.05) at the littoral stations 3 and 2 than the open water Station 1 due to the small-bodied nauplii stages, small rotifers and cladocerans particularly Bosmina longirostris. In general, species richness, evenness, and diversity increased as average abundance increased in the littoral zones of the lake. The dominant zooplankton were Bosmina longirostris, Daphnia lumholtzi, Thermodiaptomus galebi, Thermocyclops ethiopiensis, Diaphanosoma sarsi, Keratella sp., Brachionus sp., Filinia sp. and Trichocerca longiseta. The rotifers particularly, the brachionids consistently occurred at all stations and was the most dominant zooplankton group in terms of abundance and diversity. This study showed that the lake is not polluted, and has a high potential for thriving fishery