Introduction

Estuary, a tidally influenced transition zone between river and sea, is a unique ecosystem. The upstream limit to which the river turns brackish (to a minimum of 0.5 ppt) is considered upper limit of the estuary. Sedimentary movements and deposits happen in the estuary due to constant intermingling of water from the land and the ocean1, 2. Tropical estuaries with microhabitats like mangroves, mud flats, marshes, reed swamps, shell beds etc. and varied salinity conditions are good places for fishery3. The vastness of the ocean notwithstanding, several marine fishes use estuaries as nurseries for their young or feeding grounds for sub-adults and adults. Root entanglement of mangroves provides security for many fishes from predation and fishing by humans4-6. Estuary is often dominated by euryhaline and to lesser extent by stenohaline fishes tolerant of variable and narrow ranges of salinity respectively7. Estuaries today are heavily exploited and are among the most threatened ecosystems. The current study on fish diversity and distribution in relation to environmental factors, particularly salinity, in Aghanashini River estuary, is a pioneering one for Karnataka State.