耳石によるニギス産卵系群の分離の可能性

Abstract

The possibility of race separation for nigisu, Glossanodon semifasciatus (KISHINOUYE), was demonstrated and its biological implications were discussed. The otolith of nigisu showed various types, based on differences occurring in the appearance of the hyaline of opaque first growth zone, and the width of the hyaline band. The appearance of these considerable variations in the otolith type were suggested as being due, in the main, to differing seasonal growth conditions during the larval and post-larval periods. The early spawners might develop a wide hyaline zone as the first growth mark and the late spawners a narrow hyaline zone. However, if a fish is spawned at the time of the opaque zone formation, the otolith will have an opaque type of first growth region. Some differences in the growth rate between the early and the late spawning groups were estimated for each age or year class. The differences between the two groups were greater in the zero age-class than in older classes, and decreased with age.