Age validation and growth variability of Japanese flounder Paralichthys olivaceus off the Pacific coast of northern Japan

This study examined age and growth of Japanese flounder Paralichthys olivaceus off the Pacific coast of northern Japan, and determined whether the growth patterns of male and female fish in northern (40-41 degrees N) and southern (37-38 degrees 15'N) waters differ. In total 8095 specimens were collected between January 1999 and December 2005. Zonation consisting of opaque and translucent bands on the otolith was evident. Within each opaque band a thin and clear check (ring mark) was observed in all specimens examined. Monthly change in the frequency of appearance of a ring mark on the outer margin of the otolith indicates that ring marks form between July and August. The von Bertalanffy growth model showed a sexual dimorphism in growth, as females grew faster and reached a larger size than males. The growth patterns obtained by tracking the observed total length for monthly collections showed a rapid increase in total length between August and October. Spatial variation in the growth pattern of male and female fish between northern and southern waters was evident, as southern fish were significantly larger than northern counterparts during 1.25-3.00 years post hatch.