Upriver migration and environmental conditions around spawning grounds of the ice goby Leucopsarion petersii in the Mitsuo River, Hiroshima Prefecture, southwestern Japan

Abstract

Surveys for upriver migration and conditions around spawning grounds of the ice goby Leucopsarion petersii were conducted in the Mitsuo River, Hiroshima Prefecture, southwestern Japan. A set net fishing for the ice goby was operated near the river mouth from late February to late April 2016. Daily catch of the ice goby was high during the spring tide period and low during the neap tide period. Abundance of egg mass was highest at the sampling site located about 350 m upriver from the river mouth, where salinity was about 0 throughout the day in the neap tide period and increased to about 25 during high tide hours in the spring tide period. In the Mitsuo River, where the maximum tidal amplitude is about 4 m, the spawning ground of ice goby was exposed to higher salinity conditions during the spring tide period compared to other rivers flowing into the Sea of Japan with lower tidal amplitude (< 1 m). Exposure to both freshwater and brackish water seems to be an indispensable environmental factor for the formation of the spawning ground of the ice goby in the Mitsuo River.