Conclusion

Tropical estuaries in their natural states are rich in fisheries. Of the prominent environmental parameters considered in the study salinity was the most decisive in fish distribution.  The estuary as such had hardly any exclusive fish with minor exceptions. Zone I closest to sea had highest diversity as this zone experienced lowest salinity in monsoon and highest in pre-monsoon facilitating seasonal fish succession from low to high salinity species; many euryhaline ones with wider salinity tolerance ranges occupied the zone throughout the year. There is need to protect also estuarine microhabitats like mangroves, sedge areas, mud-flats, shell-beds etc. for healthy assemblage of fishes.  As regards salinity many estuaries of the west coast are seriously affected by execution of hydro-electric projects the water releases from which adversely affect salinity regimes with adverse consequences on fish diversity and fishery itself. Fishery collapse has happened in the Sharavathi estuary of Uttara Kannada,  which had only 29 fin fish species, unlike 77 in Aghanashini, attributed to year-round salinity drop due to constant fresh water releases from upstream hydro-electric projects28.  River diversion from Western Ghats, with scanty consideration for environment, particularly estuarine ecology, is a burning topic today.