Fish diversity, relative abundance and some related environmental parameters of Gilgel Gibe and Gojeb rivers, Omo-Turkana Basin, Southwest Ethiopia

Abstract

Fish diversity, relative abundance, length-weight relationship, condition factor, sex ratio, and some environmental parameters of Gilgel Gibe and Gojeb rivers were studied in two seasons. A total of 256 fish specimens were collected from both rivers during wet and dry seasons using appropriate gears. Nine fish species were identified which were included in eight genera and six families. The represented families include Mormyridae, Alestiidae, Cyprinidae, Bagridae, Clariidae and Cichlidae. Family Cyprinidae was the most diverse consisting of four species (44.4%) and all the remaining families were the least diverse represented only with one species each. The diversity of fish species in Gojeb (H’=0.691) was higher than that of Gilgel Gibe River (H’ =0.636). Labeobarbus intermedius (52.04 % IRI) in Gilgel Gibe River and (34.81 % IRI) in Gojeb River, Bagrus bajad (13.54 % IRI) in Gojeb River and Labeo forskalii (8.30 % IRI) in Gojeb River were the first three most abundant fish species, respectively. Raiamas senegalensis in Gojeb River stood the least abundant species with 0.62 % IRI. The length-weight relationships fitted for Labeobarbus intermedius (in Gilgel Gibe and Gojeb rivers), Bagrus bajad and Labeo forskalii (both in Gojeb River) using a power function.. The mean Fulton condition factor (FCF) for Labeobarbus intermedius was 1.12) in Gilgel Gibe River and 1.19 in Gojeb River. There was no significant variation (ANOVA, P > 0.05) in mean FCF of Labeobarbus intermedius in the two rivers. Bagrus bajad and Labeo forskalii that occurred in Gojeb River had mean FCF of 1.23 and 1.09 respectively. Males were more numerous than females in both rivers throughout the study period with the exception of Labeobarus intermedius fish species collected from Gojeb River. Statistically significant variation was observed between males and females for Labeobarus intermedius fish species collected from Gojeb River (Chi-square, P < 0.05). However, in case of Labeobarus intermedius collected from Gilgel Gibe River, Labeo forskalii and Bagrus bajad (both collected from Gojeb River). Statistically no significant variation was observed between males and females fish species (Chi-square, P > 0.05) from the theoretical 1:1 ratio during the study period.