Seasonal fish abundance and composition in three Thailand streams: influence of discharge

Abstract

The fish assemblage at a site in three Thai streams was sampled by electrofishing at approximately monthly intervals. Seasonal changes in fish abundance and assemblage similarity varied inversely with discharge that mirrored seasonal rainfall patterns and affected the connectivity of each stream system both longitudinally and laterally. No other habitat variable exercised a consistent effect on abundance or assemblage similarity across the three stream sites. The seasonal pattern of species richness was similar to that for abundance but was not significantly related to discharge probably due to invasions by larger river species during high discharge. Only a few species were numerically abundant, mostly cyprinids and, less often loaches, a goby or a half beak. It is suggested species occurrence at a site depends on the interactions among discharge, water depth and the physiography of the floodplain in concert with species-related behavior and limitations on physical performance.