Settling period of larvae and juveniles of Japanese flounder Paralichthys olivaceus in Shijiki bay, Hirado island.

Abstract

The spawning and settling periods of Japanese flounder Paralichthys olivaceus (Temminck et Schlegel) were examined in Shijiki Bay and its vicinities in 1986.The start and end of spawning and settlement were estimated from development-temperature relationship of laboratory-reared flounders and developmental stage composition of pelagic larvaeobtained by larva-net surveys in mid March and mid May. These analyses demonstrated that spawning would start from late January and continue until early May, and settlement from early April through early June. The settling period was also confirmed directly by beam-trawl sampling. These evidences revealed that three months of spawning season are reduced to about two months of settling period because while pelagic life is prolonged in the early season, it is shortened in the later season due to increasing water temperatures.During the two months of settling period, a large size distribution in settled flounders would inevitably occur, which would possibly cause cannibalism Furthermore, size at metamorphosis of flounder decreases considerably with increasing water temperature. These factors which are directly related to survival of settling flounders are considered important in analysing recruitment dynamics.