Title: A study of the diversity and ecology of the freshwater fishes of four river systems of Uttara Kannada District, Karnataka, India.
Author: Anuradha Bhat

The Uttara Kannada district (74o9’ to 75o10’ E longitude and 13o55’ to 15o31’ N latitude) which lies along the central part of the hill ranges called the Western Ghats, has a number of perennial as well as temporary water bodies, like tanks, pools, lakes and also streams and rivers. Four of the west flowing rivers (Kali, Aghanashini, Bedti, Sharavati) were chosen to study the diversity, distribution and ecology of the freshwater fish communities of these rivers. There has been very little work on the fish communities of this region, except for taxonomic accounts of fishes in some areas. Thus, a study on the species diversity of fish community, their composition, and distribution patterns and effects of these disturbances is much needed to put forth the statement on a need to protect and conserve these natural habitats and the existing fish diversity in these river systems.
Sampling for fish was done over a period of two years (December 1996 – April 1999) where 24 sites pre-selected for sampling on a regular basis were chosen and were sampled at different times of the year, and during both day as well as night. Sampling was done at different habitat types present at each site.

A total of 10,771 individuals belonging to 92 species were identified. Species richness comparisons across the four rivers, Sharavati has the highest species richness while that for Aghanashini was the lowest. Bedti has the highest abundance in terms of the number of individuals collected per sample (per 1000 individuals). Comparisons of species composition at the regional scale show that same regions on different rivers are more similar to each other in their fish species composition as compared to different regions on the same river. Changes in species richness as well as composition are found, along the upstream to downstream gradient in rivers, with downstream regions showing higher species richness than the upstream regions. Multivariate methods like PCA and CCA were used to study association of species compositions with environmental and stream parameters (e.g. stream width, depth, velocity, substratum characterisitcs,etc.).
The Index of Biotic Integrity, a method used for ranking sites according to the extent of human disturbances and their effect on fish community richness and composition, was used to score and rank 9 sites located on these rivers. The results of this study show that sites on Kali, like at Dandeli and Bommanahalli are the most affected by disturbances, while study sites on Aghanashini as well as Bedti seem to be fairly undisturbed in terms of their fish community composition.