2022 年 57 巻 2 号 p. 41-48
Visceral adhesions are found in sockeye salmon Oncorhynchus nerka in the North Pacific Ocean and adjacent regions. The disease is induced as the result of a host reaction associated with the migration of the freshwater philonematid nematode Philonema oncorhynchi from the host tissues to the body cavity. In this paper, 928 individuals of sockeye salmon caught in the central North Pacific Ocean and central Bering Sea were examined for their biological features and the presence or absence of visceral adhesions to study the impact of the disease on the growth of the fish. Scale patterns were also analyzed to evaluate if the disease affected the spring-summer growth of the fish in the ocean. No statistically significant difference was found in frequency distributions of fork length, spring-summer ocean growth, and condition factor between the fish with and without visceral adhesions. This indicates that the disease has no substantial negative impact on the growth of ocean-migrating sockeye salmon. This paper also discusses the previously hypothesized disappearance of the disease with fish maturation and suggests that it remains in some of mature salmon.
