Age and Growth of Pointhead Flounder Hippoglossoides pinetorum in Ishikari Bay, Hokkaido

Abstract

Pointhead flounder, Hippoglossidespinetorum, taken by commercial gillnets and an experimental beam trawl net in Ishikari Bay, Hokkaido from September 1991 to July 1993 were aged using polished otoliths (saggitae). Ages were validated by the monthly change in the percentage of otolith with translucent edge and marginal increments; a single opaque and translucent zone was formed annually. The regression method and Lee (Fraser-Lee)'s method were used to estimate the back-calculated length. Growth of pointhead flounder was expressed as Lt=251.9(1-exp-0.261(t-0.142)) for males and Lt =315.1(1-exp-0.219(t-0.200)) for females using back-calculated lengths by the regression method and Lt =251.6(1-exp-0.263(t-0.142)) for males and Lt=333.0(1-exp-0.204(t-0.186)) for females using back-calculated lengths by Lee's method, where Lt is the standard length (mm) at estimated age t. Small differences in the theoretical lengths of older female fish were found between the two methods. However, the theoretical standard lengths predicted by the two methods were very similar at most estimated ages and indicated the approximate actual length at each age.