Occurrence of deformed fish and their fitness-related traits in Kirikuchi charr, Salvelinus leucomaenis japonicus, the southernmost population of the genus Salvelinus.

Kirikuchi charr, Salvelinus leucomaenis japonicus, is the southernmost population of the genus Salvelinus. It is endemic to the Kii Peninsula, central Honshu Island, Japan. As a consequence of anthropogenic disturbances, a few populations of Kirikuchi charr with low genetic diversity now survive only in small, isolated habitats. This study investigated the occurrence of deformed individuals and assessed differences between deformed and nondeformed fish in fitness-related traits, i.e., body size, body condition, growth rate, reproductive traits, survival rate, and habitat use, for two small isolated populations of Kirikuchi charr in the upper drainage of the Totsu River system of the Kii Peninsula. The two populations contained deformed fish in the respective proportions of 8.0-17.4% and 3.0-5.8% between 2003 and 2005. Annual survival rates of deformed fish were approximately half those of nondeformed fish. Other traits were not significantly different between deformed and nondeformed fish. These results indicate that the occurrence of deformities is an important ecological indicator that reflects the decline in fitness of small, isolated populations.