Trophic status and diversity of fish species in selected tributaries of Bentota River

Abstract

Present study was carried out to investigate the, abundance and trophic status of fishes inhabiting tributaries of the Bentota River. Fish were sampled using gill nets, seine nets, cast nets and some were also collected from fishermen’s catches harvested at the tributaries of the Benthota River in Katapola, Ganegoda, Avitthawa, Yagirala and Galatara. To investigate the trophic status, stomach contents were analyzed and quantified using the Point method based on the percentage of bio volume per food category. Ten species of fish were recorded from all five sites, including two endemic species, Clarias brachysoma, Channa orientalis and one invasive alien fish Chitala ornata. Some indigenous species such as Puntius vittatus (n=400), Rasbora daniconius (n=134), Puntius dorsalis (n = 42) and Trichogaster pectoralis (n=71) were also caught in reasonable number. Parts of fish (scales, fins and flesh), mollusks, adult insects, insects larvae, macrophytes and digested/detritus matters were identified as main food categories in the stomach. Based on the gut content analysis, three feeding guilds i.e. piscivorous, herbivorous and zooplanktivorous, were identified. High diet overlap values were recorded in species pairs belonged to the same feeding guild i.e. Chitala.ornata- Channa orientalis while low diet overlap values were recorded in species belonged to different feeding guilds. Remains of fins of Channa orientalis, and Rasbora daniconius and some invertebrates observed in stomach contents of C. ornata, indicated its negative impacts on biodiversity in study sites. Therefore urgent attention should be paid to population control of C.ornata and to prevent its further invasion into new habitats.