The unique topography of North-East India and watershed pattern is an attractive field for icthyological studies. This region has already recognized as a global spot of freshwater fish diversity. A great numbers of species have been reported from most of the North-Eastern region states. River Siang is the one of the major river of Arunachal Pradesh. Mystus is a genus of small to medium-sized of the family Bagridae. There are currently 45 extant species in this genus. There are four species of Mystus are recorded in River Siang of Arunachal Pradesh, these are Mystus bleekeri, Mystus cavasius, Mystus vittatus and Mystus tengara.
