A Comparison of Secondary Sexual Characters and Age Composition of Wild and Hatchery Chum Salmon (Oncorhynchus keta) in the Yurappu River, Southern Hokkaido in Japan

摘要

Hatchery salmon may develop their secondary sexual characters less significantly than wild fish because of no opportunity of breeding competition (Fleming and Gross 1989). In the Yurrapu River, southern Hokkaido, chum salmon (Oncorhynchus keta) originated from hatchery spawn at the upper reaches (decignated as hatchery salmon), whereas possible wild chum salmon spawn at the lower reaches. We compared their secondary sexual characters and age composition amongboth populations during the fall and winter of 2005.