First Record in Japan of Fluvial Reproduction of the Alien Species Smallmouth Bass

概要

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Nine broods of smallmouth bass offspring were observed and collected in the Nogu River, Nagano Prefecture. It was also observed that a paternal fish cared for the offspring in one brood. This is the first record of smallmouth bass reproduction in Japanese streams.<BR>The mean standard lengths of offspring ranged from 9.8 to 22.8 mm in each brood. Current velocities were measured at interval of ca. 75 cm from 6 to 10 sites across the stream adjacent to the location of each brood. Maximum current velocities that the offspring can swim against the current ranged from 3.2 to 61.1 cm/s adjacent to the location of each brood. Their distribution extended to areas with faster currents with their growth, and youngest larvae (flexion larval stage) were limited to areas with slow currents. It seems that slow current areas are necessary for smallmouth bass spawning.<BR>A significantly higher ratio of smallmouth bass to largemouth bass occurs in the Nogu River than in Lake Kizaki indicating that smallmouth bass have a higher adaptability to the environment of Japanese stream. This indicates that smallmouth bass can readily establish and may disturb Japanese stream ecosystems.
日本水産増殖学会の論文