Diversity Relative Abundance And Biology Of Fishes In Beles And Gilgel Beles Rivers Abay Basin Ethiopia

Diversity, relative abundance and biology of fish species of Beles and Gilgel BelesrnRivers were studied during November 2005 to May 2006. Physical and chemicalrnparameters were also measured during this study. Fishes were sampled using gillrnnets of various stretched mesh sizes, and hooks and lines. Identification of fish wasrnmade to species level by comparing the sample characters with taxonomic keysrnfound in literatures and specimens deposited. An index of relative importance (IRI)rnand Shannon diversity index (H`) were used to evaluate relative abundance andrnspecies diversity of fishes, respectively. Mean temperature, river width and secchirndepth showed apparent longitudinal trends. A total of 1124 individual fishesrnbelonging to 5 orders, 7 families, 13 genera and 23 species were caught in Belesrnand Gilgel Beles Rivers. Cyprinidae was best-represented family with the highestrnnumber of fish species in the rivers while Labeo and Labeobarbus were the bestrepresentedrngenera. A higher number of species were recorded in the Beles Riverrn(22 species) than in the Gilgel Beles River (5 species). L. nedgia, L. forskalii, L.rnintermedius and O. niloticus were found in both rivers. The diversity index wasrnhigher in the Beles River (H´=2.43) than in the Gilgel Beles River (H´ = 0.88).rnAmong sampling sites, diversity index was highest at Babizenda (H’ = 2.32) andrnlowest at College (H’ = 0.76). Cyprinidae was the most dominant family in Belesrnand Gilgel Beles Rivers. L. intermedius was the most abundant species according tornIRI (38.86%), while L. forskalii was second (24.68%) and L. bynni third (18.36%)rnin total catch. L. intermedius was the most abundant species in the total catchrnduring the wet season, while L. forskalii in the dry season. L. intermedius had betterrnmean % IRI in Gilgel Beles River than in Beles River (P < 0.05). However, therernwas no significant difference in % IRI between the two rivers for L. nedgia, L.rnforskalii and O. niloticus (P > 0.05). L. forskalii showed isometric growth while L.rnintermedius exhibited positive allometric growth in Beles and Gilgel Beles Rivers. L.rnforskalii and L. intermedius were found to be in better condition in both riversrn(ANOVA < 0.05). Females were in better condition than males in both rivers. L.rnforskalii had a better condition factor (FCF) in the dry than in the wet season (ANOVA < 0.05). However, L. intermedius had better mean FCF in wet than in dryrnseason (ANOVA > 0.05). Females were more numerous than males in the totalrnsexed specimens. Absolute fecundity of L. intermedius increased with an increase inrnfish size, and ranged from 1535 to 13864 with a mean of 3173 eggs. In general,rnBeles River is richer than Gilgel Beles River, in terms of total numbers of fishrncaught and number of species recorded. In order to have a better knowledge of thernfish populations in the study area, further studies are required on diversity,rnabundance and biology of the fishes.rnKey words/phrases: Rivers, Beles, Gilgel Beles, relative Abundance, diversity,rnLength-weight relationship, Fulton condition factor, Fecundity, Sex ratio.

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