In scuba dives off the Island of Maui, near Olowalu, a high incidence of tumors was observed in the butterfly fish (Chaetodon multicinctus). Incidences of 25% (January 1976), 22% (June 1976), 22% (August 1977) and 23% (January 1978) were observed over the two-year period of study. Observations of fish with tumors were localized to an area approximately 180 m wide and from 20–685 m from the shore. Of 11 species of butterfly fish seen in the study area, only the C. multicinctus was involved. C. multicinctus examined in areas adjacent to the study area were free of tumors. Sixty-seven fish with tumors were obtained for laboratory study. One to 6 tumors per fish were seen only in the skin, ranging in size from 0.1 to 2.5 cm. Microscopically, smaller lesions were hyperplastic while the larger lesions were diagnosed as benign fibromas. Electron microscopy of a few tumors did not reveal the presence of virus. The cause or causes responsible for the occurrence of these high incidences of tumors in only one species of butterfly fish in a localized site in Hawaii is unknown.
