The present study made clear the distribution and the frequency of tumorous flatfish and goby in the coastal waters of Hokkaido, Japan. The tumorous fish had the histological characteristic of having X-cells in the epithelial lesions. The species having these tumorous lesions were Kareius bicoloratus, Limanda schrenki, Platichthys stellatus, Cleisthenes pinetorum herzensteini, Hippoglossoides dubius, Verasper moseri, Liopetta obscura among flatfish, and one species of goby Acanthogobius flavimanus.
The tumorous flatfish were distributed in the coastal waters of the Japan Sea side from Teshio to Soya Bay, and on the side of the island facing the Okhotsk Sea, teh Nemuro Strait and the Pacific Ocean, from Kushiro to the city of Nemuro. The tumorous gobies A. flavimanus were collected only at Nanachama Shore, Hakodate Bay. The highest frequency recorded was 40% for P. stellatus from Lake Tofutsu.
Yearly changes in the frequency of tumorous fish were recognized for L. schrenki from Tokotan on the Nemuro Strait, for K. bicoloratus from Soya Bay, and also for A. flavimanus from Hakodate Bay. Species specificity was recognized in the tumorous infection of flatfishes.
This tumorous infection may be endemic. The high frequency of these tumorous fishes is not directly related to municipal or industrial discharge, but to muddy bottom caused by stagnted sea water.
