"Advanced spawning of the flounder, Paralichthys olivaceus, in an indoor tank with combined manipulation of water temperture and photoperiod."

"The flounder, Paralichthys olivaceus is one of the most important marine fishes cultured in Japan. The flounder is not so tolerant to high water temperature and mortality increases above 28degC. Then, it is profitable to raise the flounder of marketable size until next spring. Therefore, advanced spawning for early seedling is desired. In order to obtain basic informations on the. control of spawning, especially on the effects of water temperature and photoperiodism, two series of experiments were conducted in 1985 (Exp. 1 ) and 1986 (Exp. 2 ). An indoor broodstock tank (20 cube m ) equipped with a circulatory apparatus and a controlling system of water temperature and photoperiod was used for the experiment together with an outdoor tank (20 cube m) for comparison. In Exp. 1, both water temperature and photoperiod were manipulated so as to advance two months earlier than the natural water temperature and photoperiod respectively. The spawning at the experimental tank started on Jan. 27, which is 42 days earlier than that of the outdoor tank, and continued for 67 days until Apr. 3. .Total number of spawned eggs was 21.3 million. Initial spawning occurred at 14.1degC, and terminated at 15.4degC. In Exp. 2, only photoperiod was manipulated so that the day length would be 17 hours from 6a.m. to 11p.m. without manipulation of water temperature. Initial spawning occurred on Dec. 5, which is 48 days earlier than that of the outdoor tank, and continued for 105 days until Mar. 18. Total number of spawned eggs was 30.6 million, the spawning began at 19.1degC, and it terminated at 14.1degC. In Exp. 1, it is certain that the manipulation of water temperature advanced spawning season. While it is uncertain whether the manipulation of photoperiod affected it or not. In Exp. 2, it is clear that the elongation of photoperiod without manipulation of water temperature accelerated the spawning period. It is left for future study to precisely investigate the combined effects of water temperature and photoperiod (e.g. the extent of elongation of the photoperiod and the time of onset to manipulate it) on the advanced spawning season for establishment of advanced spawning technology."