The biodiversity of inland is alarmingly declining primarily due to unsuitable and unethical fishing practices prevalent in the rivers and streams. A variety of destructive type of fishing activities are being practised in the inland water bodies of Kerala such as poisoning using chemicals, insecticides and seeds of plant origin, dynamiting, electric fishing etc. This creates various new and intense pressures leading to decline in species number. The Poonthura backwater in the south west coast of India (Kerala state) is a typical estuary. It is located at a latitude between 8° 25’ and 8°3’N and longitude 76° 55’ and 77°00’E. This estuary is circular in shape enclosing an island called Edayar. This is separated from the Lakshadweep Sea by a sand bar at Poonthura which opens during the monsoon period consequent to heavy discharge of water from the adjacent rivers. In the present study the biodiversity survey of fish and shellfishes of this backwater was carried on for one year (April 2013 to March 2014). The data on fish community collected during the surveys were correlated with the physico-chemical parameters, nutrients of the water samples, carbon, nitrogen and phosphorous and heavy metals such as copper, lead, manganese, nickel and zinc of the sediments. A total of 32 species were reported during the whole year. All the fish and shellfishes showed seasonal influence with more fresh water species in monsoon months. The marine fishes occur more during pre monsoon. The pre monsoon reported less percentage and non availability of most of the fish species in catches. The analysis of the condition of fishes is of considerable significance in determining the cycle of changes related to other biological aspects of fishes such as feeding and breeding. By virtue of their position at the interface of sea, river and land, estuaries support a distinctive assemblage of birds, fishes, invertebrates as well as characteristic floral communities such as mangrove swamps and salt marshes. The physico-chemical properties in relation to catchment status with condition of the estuary were determined. The correlation analysis proved that, there is a relationship between environmental parameters and survival of the species in those ecosystems.

biodiversity, environment, heavy metal, nutrients, sediment and species