池産ビワマスとアマゴの血中チロキシン濃度の季節的変化〔英文〕

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Seasonal changes in plasma thyroxine concentrations were examined in biwa Oncorhynchus rhodurus and amago salmon O. rhodurus reared in the pond. About 80% of biwa salmon lost parr marks and became silvery in underyearling June. Thereafter, they kept silvery body color until 2-year-old April, when the experiments were terminated. Plasma thyroxine levels in biwa salmon decreased gradually from underyearling spring (about 4 ng/ml) to autumn, reached a lowest level (0.4 ng/ml) in December, and then increased gradually until yearling October (3-4 ng/ml). The relatively high hormone concentrations during underyearling April and May could be related to the body silvering and downstream migration. On the other hand, about 30% of amago salmon became silvery smolts with full seawater adaptability in underyearling autumn and winter. Plasma thyroxine concentrations in amago salmon showed a clear rise during smoltification and a distinct peak at the time of new moon in October (about 8 ng/ml). Thyroxine concentrations were re-latively high prior to the spermiation of precociously matured males (underyearlings) of both biwa and amago salmon, but decreased to a low level during spermiation, suggesting that thyroid hor-mone may also be involved in gonadal development.
日本水産學會の論文