Total relative abundance of fish and species
richness at 95 sites in small rivers varied significantly
with physicochemical factors. Species richness was
negatively and positively related with pH and dissolved
oxygen, respectively. Relative abundance
varied inversely with discharge and ambient ammonia
and, directly with depth, substratum, ambient oxygen
and alkalinity. Fish were represented by 62 species,
the most common being Rasbora paviei, Puntius
binotatus and Channa gachua. Canonical correspondence
analysis related species and their relative
abundances with eight environmental variables into
four groups. The most species-rich group was
associated with approximately average values for the
significant variables. The group with the fewest
species was associated with high oxygen and low
ammonia and alkalinity. The other two groups had
similar numbers of species, one being associated with
high ammonia and alkalinity and low oxygen. Species
in the other group were found at locations where
rivers were relatively wide with comparatively high
oxygen and low ammonia concentrations.