POTENTIAL IMPACT OF WATER QUALITY AND HYDROLOGY ON FISH COMMUNITY IN UPPER MALWATHU OYA, SRI LANKA

Malwathu Oya is one of the biggest river basins in Sri Lanka. River discharge fluctuates throughout the year due to variations in weather conditions in its catchment. The quality of its water is also affected due to anthropogenic activities in the area. Changes in hydrological and physiochemical factors of water can affect the ichthyofauna in this fluvial environment. The objective of this study was to identify the relationships between fish species richness and Shannon diversity index in relation to five selected physicochemical (nitrate, phosphate, chloride, dissolved oxygen and temperature) and two hydrological factors (River width and discharge) in upper Malwathu Oya. Study was carried out in twelve sampling sites for the period of two years. Fish, water sampling and hydrological parameters were detected monthly. Linear regression was used to examine the relationships between individual physicochemical parameters and hydrological factors with species richness and Shannon index. Significant positive correlations were observed between species richness and chloride (r2=0.12), nitrate (r2=0.39), phosphate (r2=0.16), dissolved oxygen (r2=0.15) and river width (r2=0.07). Shannon index showed significant positive correlation with chloride (r2=0.11), nitrate (r2=0.33), phosphate (r2=0.14), dissolved oxygen (r2=0.16) and river width (r2=0.20). However, temperature showed an inverse significant (P<0.0001) relationship with species richness and Shannon index. Increasing discharge results in an increase of river width. Significant linear relationship was not found between species richness and river width as well as between river discharge and species richness and river discharge and Shannon index. Nevertheless, the linear relationship between Shannon index and river width was significant (P<0.02). Results of the multiple linear regression showed that only three variables (nitrate, chloride and temperature) were significant to the model with the total R2 of 48.7%.