Histological sections of skin of fishes O. argenteus, J. maculatus, P. diacanthus and J. dussumeri indicated that infected skin was severely damaged by protozoan parasites. Tha damage caused was indicated by erosion, separation, dsilocation of epidermis, shrinkage, atrophy of tissue, abscess formation, hyaline degeneration and destruction of muscle fibres. Skin damage was more or less similar to some extent in O. argenteus, J. maculatus, P. diacanthus and J. dussumeri. Cluster of protozoans was observed in most of the sections. In J. dussumieri no clusters of protozoans were observed. While it was observed in O. argenteus, P. diacanthus and J. maculatus. This information is based on original research work and is valuable to marine fish parasitologists, researchers, teachers and students working in this field of study.