OSMOTIC RESPONSE OF A CICHLID FISH, Etroplus suratensis FROM ASHTAMUDI LAKE (RAMSAR SITE) TO VARIED SALINE CONDITIONS

Osmotic response of a cichlid fish, Etroplus suratensis collected from two different sites of Ashtamudi lake (Ramsar Site) was observed by deploying the activity of branchial Na+-K+/ATPase enzyme. Of the two sites selected for the study, viz. Munrothuruthu (Site I) and Mukkad (Site II), marked variations in the activity of the enzyme under laboratory acclimatized saline conditions was observed. It is suggested that fish inhabiting Site I experienced a fresh water habitat as the River Kallada pours its water into this site. Fishes from Site II, located near the bar mouth and exposed to the influx of sea water, are always facing a contaminated environment owing to the discharge of domestic wastes and oil by-products discharged from the mechanised vessels harbouring Neendakara estuary. The results based on data collected from Site I fish exhibited less tolerance to varied saline conditions whereas Site II fish survived at almost all changes in salinity.