Assessment of fish diversity and composition in alwero reservoir, baro akobo basin, southwest Ethiopia

Abstract

This study was conducted to assess diversity and composition of fishes, identify relative abundance, and determined the length weight relationship and condition factor for the most abundant fish species in Alwero Reservoir located in Baro-Akobo Basin, Gambella Region, Southwest Ethiopia. Additionally, some environmental factors related to fish abundance were also studied. Fish specimens were collected from selected sites using gill nets of various mesh sizes (6cm, 8cm 10cm, 12cm, 14cm, 16cm). Fish sampling was done in two months, one for dry season (May, 2018) and one for wet season (October, 2018). A total of 427 specimens were caught from the reservoir. These were identified into 17 species, 16 genera, 13 families and 6 orders. Shannon diversity index for the reservoir is 1.6. Family Mormyridae was the most diverse consisting three species. Cilchlidae, Citharinidae, Alestiidae and Auchenoglanidae were the best represented families with respect to abundance constituting 223(52.2 %), 84 (9.67%), 36 (8.43%) and 26 (6.09%) of the total catches respectively. Oreochromis niloticus (63.78% Index of Relative Important), was the most represented fish species in terms of number, weight, frequency of occurrence and Index of Relative Important in Alwero reservoir. Analysis of the Length-weight relationship for the most abundant species showed that the relationship was strong by reffering b-value for Oreochromis niloticus (b-3.027) attains isometric growth, positive allowmetric growth for both Brycinus macrolepidontis (b-3.228) and Auchenoglanis occidentalis (b-3.195) and negative allowmetric growth for Citharinus citharus (b-2.85). Seasonal variations in the mean Fulton Condition Factors of the most dominant species were statistically significant (P<0.05). In the present observation, most of the physicochemical parameters of reservoir were conducive for growth of fish fauna. Chlorophyll a, pH and temperature appeared to be the most important in the structure abundance of fish species among measured environmental factors in CCA analysis. Since some variables are negetively correlated, extra analyses on environmental factors are neccessary to give inclusive results on which parameters are the most important.