Lepidological Study on Sea-run Specimens of Oncorhynchus rhodurus

Abstract

A lepidological study on sea-run specimens of Oncorhynchus rhodurus obtained from the Nagara River and Ise Bay was performed in comparison with the biwamasu (a lacustrine form of O.rhodurus), the amago (a fluviatile form of O.rhodurus), the sakuramasu (a sea-run form of O.masou) and the yamame (a fluviatile form of O.masou).The scale of the smolt of sea-run specimens of O.rhodurus has an unequal growth in width and length, and also in apical and basal areas, shifting the relative position of the focus.In the biwamasu, ridges are formed in the apical area as well as the basal area, but in the sakuramasu, many ridges are semicircular, disappearing in the apical area.In sea-run specimens of O.rhodurus, some ridges disappear in the apical margin in almost all specimens.So that, apical ridge formation in sea-run specimens of O.rhodurus is considered to be in an inter-mediate condition between the biwamasu and the sakuramasu.In the amago, apical ridge formation resembles that of sea-run specimens of O.rhodurus, and in the yamame, it resembles that of the sakuramasu.