Production of juvenile marine finfish for stock enhancement in Japan

Utilizing the potential and untapped productivity of the sea through the development of stock enhancement technology has a long history in Japan. In 1997, of the 88 species of seed produced in Japan by 284 facilities, 73 species were released. The total numbers of finfish seeds produced and released were 97 million from 36 species, and 71 million from 30 species, respectively. Over 10 million seed were produced for each of three finfish species: Japanese flounder ( Paralichthys olivaceus) and red sea bream ( Pagrus major), which have been developed throughout Japan, and black sea bream ( Acanthopagrus schlegeli), which has been developed only in the Seto Inland Sea region and the Japan Sea region. Steady progress made by stock enhancement programs, based on the release of hatchery-raised juveniles, has highlighted the importance of physiological, morphological, and ecological characteristics of the hatchery-raised juveniles in the effectiveness of the release operations. Fish health (or physiological wellness) and fish quality (or ecological robustness, described in terms of behavior and feeding activity) determine the ability of hatchery-raised juveniles to adapt to natural conditions in released environments. The releasing time, which is dependent upon the spawning time, is another important factor affecting the recovery rate of released hatchery-raised seed. Technological development of broodstock management is in induced spawning techniques, including manipulating temperature and photoperiod. Technological development of seed production in Japan has shifted its focus from quantity to quality, since health and adaptability of hatchery-raised seed are the most important factors determining the recovery rate. As a result, the focus of development of stock enhancement technology for the Japanese flounder and red sea bream is on raising the quality of health and the adaptability of the seeds.