1Graduate School of Science and Technology, Nagasaki University, Nagasaki 852-8521, 2Institute for East China Sea Research, Nagasaki University, Nagasaki 851-2213, Japan
The effect of low temperature on size-dependent overwinter mortality in the young (mainly age 0 and 1 year) mudskipper Boleophthalmus pectinirostris was examined by field investigation of overwintering habitat and acute cold-tolerance experiments. The young mudskipper were found from 5.0-55.0 cm in mud depth at Rokkaku River, Saga Prefecture and 4.5-39.0 cm at Tojin River, Kumamoto Prefecture. There was no significant correlation between body size and overwintering depth, showing that young mudskippers use shallow-mud habitats where the temperature sometimes declines to the lethal level, irrespective of size. In the cold-tolerance experiments (3°C, 5°C and 7°C), the fish died earlier under lower temperature condition but no size difference of mortality rate was detected under all temperature conditions. Thus, the size difference of overwinter mortality is probably not due to overwintering depth and acute cold tolerance.