Age, Growth and Stock Status of Robust Tongue Sole Cynoglossus robustus Gűnther, 1873 in Japan Determined by a New Otolith Observation Technique

An ageing methodology was developed and used to examine age composition of robust tongue soleCynoglossus robustus Gűnther, 1873 stocks inhabiting the Seto Inland Sea, Japan. Our sectioning and etching methods were powerful tools for identifying annual checks in otoliths, which were confirmed by scanning electron microscope observation of the otolith fine structure. These checks formed during the spawning period were also seen in immature fish. Using this new ageing methods, the age-length relationships and parameters for the von Bertalanffy growth function of male and female fish were determined to be L∞ = 324 mm and 351 mm and k = 1.16 year^–1 and 1.05 year^–1, respectively. The age composition of the populations studied and of the landings of the bottom trawl fisheries showed the percent spawning potential ratio (%SPR) to be approximately 30%. Thus, fast growth of this species would maintain the population, even under fishing pressure.