Habitat characteristics of the cyprinidae in small rivers in Central Thailand

Cyprinids were sampled, by electrofishing, from 159 sites on small rivers in four major watersheds across central Thailand. Total abundance, estimated by the depletion method, varied directly with water velocity and, inversely with discharge while species richness varied inversely with habitat width and, directly with ambient oxygen and alkalinity. Numerical abundance of cyprinids was well above that for any of the other 27 families of fishes represented in the catches. Incidence of occurrence was high only for a few cyprinid species in each watershed with most species present in ≤10% of the sites. Across all sites, cyprinids represented approximately 35% of all species captured and were absent from only two sites. Species richness was highest in the Maeklong watershed. Canonical correspondence analysis identified five significant habitat variables, temperature, habitat width, discharge, ambient oxygen and alkalinity, and the extent to which each influenced the distribution of the 41 cyprinid species. The results are discussed in relation to environmental factors and ecological adaptations.