Terapon jarbua, a marine teleost attaining a length of 25 cm, is abundant in the estuaries of the tropical and subtropical Indian Ocean. Fish scales removed from living fish are the most important food and represent the utilization of a niche previously unrecorded in the marine environment. Laboratory experiments show thatT. jarbuacan digest fish scales which have a relatively high energy content of 2cal mg−1and further that the scales are removed only from living fish and not collected off the bottom or from dead fish. The scales are taken under natural conditions from fish larger thanT. jarbuaand slow swimming species are favoured.T. jarbuaalways attacks the lateral surface of the prey species and scales are removed mainly from the posterior region of the body, particularly around the caudal peduncle. A variety of species are attacked. The black longitudinal stripes ofT. jarbuafade during feeding but in the presence of conspecifics darken. This colour pattern, which is unique among south east African estuarine fish, together with the small size ofT. jarbuascales, may prevent autopredation. It is suggested that the scale‐eating habit ofT. jarbuaarose as a modified form of predation or as an extension of ‘cleaning’ ectoparasites from the scales of larger fish. Ectoparasites are relatively common in the diet ofT.