First Microchemical Examination of Abnormal Otoliths of Amphidromous Ayu Plecoglossus altivelis

摘要

The ayu Plecoglossus altivelis is an annual fish that spawns in freshwater in autumn. The larvae drift downstream to overwinter in coastal waters and then migrate upstream as juveniles in spring (Tsu-kamoto et al. 1987). Landlocked populations are known from Biwa Lake (Azuma 1973) and several other lakes in Japan, in addition to the typical am-phidromous populations. Juvenile ayu have been stocked extensively in many rivers as they are an important freshwater fishery species in Japan. However, some ayu are found to have abnormal otoliths, and little is known about their detailed morphology and microchemistry. We examined the morphology and microchemical concentrations of some common elements (Sr, Ca, Na, K, and S) of abnormal otoliths in ayu and consider the possible factors influencing otolith abnormality.