Fish diversity and relative abundance at mesohabitat level in Gumara River, Lake Tana Sub-basin, Ethiopia.

Abstract

Information regarding fish diversity and relative abundance at mesohabitat level plays important roles in monitoring, protecting or managing fish populations and their habitats. Although the presence of different fish species has been reported in Gumara River by various studies, organized information on abundance and diversity of fish species at mesohabitat levels were not available. Such information is very important for the management of the declining fish fauna of Lake Tana. So, this study aimed at investigating the abundance and diversity of fish species at the mesohabitat level. Diversity and relative abundance of fishes have been studied in the Gumara River and its tributaries from November 2018 to April 2019. Physico-chemical parameters of water were measured using the in-situ multi-probe system. Fish sampling was conducted using a technique called point abundance sampling by electrofishing. Fish species identification was done by using reference books and specimens deposited in the laboratory at Bahir Dar fisheries and other aquatic life research center. A total of 3,880 fish specimens were collected from all sampling sites. Among the collected specimens, the most (53.14%) and least (0.26%) dominant were Enteromius humilis and Labeobarbus intermedius, respectively. Both of them are cyprinids. In addition to cyprinids, specimens from family Cichlidae (O. niloticus) and Clariidae (C. gariepinus) were examined and contributed only 0.67 and 0.34%, respectively. There was a significant variation in the abundance of species between habitats and sampling months. Shannon’s index (H'=1.21) and evenness value (J'=0.53) in the Gumara River indicate moderate pollution and uniform distribution of individuals. Among the six sampling sites, the highest (H'=1.30) and lowest (H'=0.94) diversity indices were recorded at sites in the upstream near Wanzaye hot spring and below the bridge, respectively. In terms of mesohabitat, the species diversity and evenness were higher in riffle (H'=1.25, J'=0.57) than run (H'=1.15, J'=0.55) and the pool (H'=1.11, J'=0.50). The result revealed that the abundance and diversity of fish in Gumara River varied between sites and mesohabitats and this might be due to attitudinal difference, physico-chemical parameters and impact of different human activities around the river. Therefore, emphasis should be given to the factors which may lead to the collapse of the fish habitats, especially water abstraction for irrigation. Detailed studies on the diversity, abundance, reproductive biology by collecting yearround data should be done to use them as management tools.