Composition, Abundance and Distribution of Fishes in Onah Lake, Asaba, Nigeria

Abstract

A comprehensive survey of the itchyofauna of Onah Lake was undertaken to provide data on the composition, abundance, distribution, diversity and ecological structure of this perennial freshwater body, located west of the River Niger flood plain. Fish sampling was conducted monthly between January 2000 and December 2001. A total number of 2,682 specimens belonging to 35 genera, 25 families and 46 species, were encountered. Spatial variation in fish catch revealed that station ‘A’ recorded 880 specimens; station ‘B’ recorded 793 specimens while station ‘C’ recorded 1009 specimens. The least number of taxa (36) and specimens (793) were encountered in station ‘B’ which also showed the poorest richness (9.46) in species composition. The ponderal index revealed that Citharinus citharus and Sarotherodon galilaeus contributed 16.1%; 13.4% and 10.3%; 10.1% respectively of the total fish catch by number and by biomass. They were the most dominant species.  Four out of the nine rare species recorded were restricted to station ‘C’ while the other members of this group were encountered in two or three stations; the rare species contributed 19.6% by number and 1.37% by biomass.  The analysis of variance revealed that fish abundance varied significantly (P < 0.05) among the stations across the months. Fish catch was significantly higher (P < 0.05) in the dry season (1452 ± 67.07) than the rainy season (1230 + 46.33).