Based on the scattered but scanty literature, 12 genera and 23 species of fish-leeches of the family Piscicolidae are known to be infesting a wide variety of fishes and turtles of the Indian Ocean, the adjacent seas and the river mouths. A key for the identification of these fish-leeches to the species and a synopsis of information on each species including their records, size and colour ranges, hosts, biology and behaviour and geographic and host distribution in and outside the limits of the Indian Ocean are all provided. Some general observations concerning the ecology and the relationship of these fish-leeches are included.