Upstream migration of Cottus reinii (Cottidae) from Lake Biwa to the Ado River, central Japan, in spring and early summer.

The sculpin Cottus reinii, inhabits the Lake Biwa area, central Japan, and its upstream migration features, i.e., season, body size, and gonadal condition, were investigated in an inflowing river, the Ado River, in spring and early summer. The upstream migration was observed between March and June. It showed a peak in late March and terminated by late July. The standard length (SL) of the migrants ranged from 2.4 to 11.0 cm SL and individuals of 3-6 cm SL were abundant. The migrants were mostly one year old and immature. Almost all fish larger than 6 cm SL were mature in both sexes in March and April. These results suggest that the migration of the species from Lake Biwa to the Ado River may begin and terminate in relation to water temperatures in the river and lake, and almost immature migrants remain and grow in the river. [ABSTRACT FROM AUTHOR]