Stream Fish Assemblages Along the Longitudinal Gradient of the Nyangui River.

This study investigated the influence of longitudinal and environmental gradients on fish biodiversity in a central African context. The Nyagui River was used as a study site. Fish and microhabitat data were collected at fourteen stations in three periods of different flow. A total of twenty-four species were collected including Mesobola brevianalis that was not previously documented in the lower Zambezi system. A number of species that were expected to occur at low altitude were not collected during this sampling period. Species richness, diversity, and relative abundance increased from upstream to downstream in all sampling months and this was related to increasing catchment area. The number of species and their relative abundance was also correlated to habitat diversity that was calculated using the Shannon Diversity index and this relationship was explained by a power curve and was significant in October and November. Altitudinal difference in species composition was also exhibited. The most abundant species, accounting for >50% of the total catch, at altitude >1 400m were Barbus paludinosus, Micropterus salmoides and Clarias gariepinus while at lower altitude (