Fishes constitute almost half the total number of vertebrates. Of the c 39,900 vertebrate species known to exist so far, 21.723 are living species of fishes; of which, e 841 are of freshwater and the rest, 11,650 are marine species. In the Indian region, alone, of the e 2500 species, 930 are freshwater inhabitants and 1570 are marine.

Most of the present-day fish fauna is said to have descended from the Pleistocene migrants. The subject assumes further importance and interest in view of fact that, some of the major river systems in North-East (NE) India flow between terrains of India, Myanmar and Bangladesh; indicating, thereby, that, fishes of NE India contains both Myanmarese and Bangladeshi elements. And, further, it is quite probable thea the fish fauna of N.E.India serves as an important link between those of Far-East Asia and the Indian Sub-continent.

The N.E. Region of India is considered as one of the Hotspot of Freshwater Fish Biodiversity in the World. However, there have been drastic reduction in the abundance of freshwater fishes in the region due to many reasons; notably, destruction of habitats, unsustained over-exploitation, dreadful fish diseases like the Epizootic Ulcerative Syndrome (EUS) caused by various pathogens and parasites and other anthropogenic causes. Still further, 'fish' is one of the principal staple food items and rich source of animal protein for the people of fish-eating regions.

Lack of a comprehensive treatise on the parasites in fishes in this region has prompted this humble piece of work and the authors will consider themselves to be amply rewarded if this humble piece of work proves to be useful for those it is meant.