Fukushima Prefectural Fisheries Experimental Station, Iwaki, Fukushima 970-0316, Japan
The maturation rate and the spawning period of flathead flounder Hippoglossoides dubius off Fukushima Prefecture, which were caught from 2004 to 2006 (n=7,341), were studied. The maturation rate of females was studied by the macroscopic observation of gonads and otolith aging. Estimated maturation rate was 50% at a total length of 29.9 cm, 36% in 5-year-olds, 67% in 6-year-olds, and >90% in ≥8-year-old fish. Our results suggest that female flathead flounder off Fukushima Prefecture mature at a shorter total length and lower age than those in the western Sea of Japan and Funka Bay. The spawning period was estimated to be from early February to late April with a peak from early February to late March.