IMPACT OF HYDRO-ECOLOGY ON FISH MIGRATION IN SELECTED EAST COAST ESTUARIES UTPAL BHAUMIK, N. P. SHRIVASTAVA, B. B. SATPATHY, M. K. MUKHOPADHYAY AND A. P. SHARMA Central Inland Fisheries Research Institute, Barrackpore, Kolkata - 700 120 Received : 24.11.2010; Accepted : 04.02.2011 Attempts were made to identify the commercially important migrant fish species and study their migration pattern in two selected estuaries i.e. Hooghly and Mahanadi on east-coast facing the Bay of Bengal Sea. Nearly 20 species in such category could be enlisted from Mahanadi estuary, which were also encountered in the Hooghly estuarine system. Most of the migrant species were amphidromous and their estuarine migration was influenced by the hydro-ecological characteristics. Salinity, depth and food niches were amongst the factors governing migration of the fishes. Migration was limited to 35 km in Mahanadi while up to 100 km in Hooghly estuarine system. Hilsa was only anadromous species migrating to freshwater river course and got struck up by the barrages. In Mahanadi river-estuarine system migration of Hilsa was seriously affected. Recruitment and fisheries of Hilsa in Hooghly-Bhagirathi system did not show significant impact of the Farakka barrage. Key words : Hydro-ecology, migration, estuary, amphidromous J. Inland Fish. Soc. India, 43(1) : 1-9, 2011 Introduction Migration is natural instinct and facilitating act in fulfillment of bio-physiological urges in animals. Fishes are no exception and constitute one amongst the distant migrating groups in aquatic sphere. For some fish species migration is intra environmental, limited to shorter range of distance while for others trans-environmental migration extends from a few hundreds to thousands of kilometers. Estuaries being intermediate environment between sea and freshwater river and eco-biologically rich habitat, play as favourable destination for both marine and freshwater fish species. The fish move to estuarine environment in search of breeding and nourishment habitats or for feeding and fattening purposes. The variability of estuarine environment and eco-biological richness depend on several intrinsic and extrinsic factors. Post independence habitation, agriculture and industrial development activities and consequential increase in dependence on rivers and also estuaries gradually encroached upon these resources and interfered the process of natural renewal of eco-biological potentialities. As a result the natural biotope of the estuarine system got affected in qualitative and quantitative richness including those of fishes. According to the available records the fish faunal structure in most of the estuarine systems has shown shifting trend indicating disappearance of a few species, decline in abundance of many and appearance of some species not recorded earlier. In view of this striking phenomenon in fish species spectrum it was felt necessary to develop knowledge on migration of fishes and investigate the habitat requirements, purpose and constraints in migration of fishes in or through estuarine systems. Materials and methods Two estuarine systems on east coast facing the Bay of Bengal Sea, which are hydro-morpho- 1