Diversity, Relative Abundance, Species Composition and Some Biological Aspects of Fishes in Gilgel Abay and Andassa Rivers, Blue Nile Basin, Ethiopia

Abstract

Diversity, relative abundance and some biological aspect of fishes in Gilgel Abay and Andassa Rivers were studied from September 2010 to June 2011 by using gillnets of mesh sizes 6 cm, 8 cm, 10 cm and 12 cm, monofilaments of different mesh sizes, cast net, hook and lines. Fish species identification was done by using literature and specimen deposited in the laboratory. Abiotic parameters such as temperature, conductivity, pH, total dissolved solids and transparency of the rivers were also taken, using multi-meters. The analysis of independent ttest showed that there was significant deference in pH and transparency between seasons in Andassa River (p<0.05). In Gilgel Abay River, there was significant difference in temperature and transparency (p<0.05) between seasons. Totally 939 fish specimens were collected from Gilgel Abay and Andassa Rivers. Three families and thirteen species of fishes were identified from Andassa and Gilgel Abay Rivers. Labeobarbus intermedius, Varicorhinus beso, L. nedgia and Clarias gariepinus were the most dominant fish species found in both Rivers. Index of Relative Importance (IRI) and Shannon Diversity Index (H') were used to evaluate the abundance and diversity of fish species. Andassa River had higher diversity (H'=4.06) than Gilgel Abay River (H'=4.05) in dry season but lower than Gilgel Abay in wet season which was (H'=3.32) and 4.35, respectively. In wet season, the most abundant species in Andassa River were L. intermedius, V. beso, C. gariepinus and L. crassibarbis. L. intermedius, L. nedgia and C. gariepinus were the most abundance species in Gilgel Abay during wet season. In both seasons, L. intermedius was the most important species at Andassa and Gilgel Abay Rivers. In Gilgel Abay River, the most important fish species in wet and dry seasons were L. intermedius, L. nedgia and C. gariepinus. The sex ratio analysis showed that there was significant deviation from unity (p<0.05).