Abstract
Spawning inducement of flounder, Paralichthys olivaceus, was attemped by the control of water temperature and photoperiod from June 1, 1989 through January 5, 1990 (189 days) Water temperature was gradually decreased from $21.7^{\circ}C$ to $10.6^{\circ}C$ which was the minim biological temperature for spawning of flounder. Water temperature was increased asain to $15^{\circ}C$ gradually, and then maintained at this level through the end of spawning. Photoperiod was also changed gradually from 10L/14D in June 1, 1989 to 14L/10D in July 25, 1989. Spawning of the fish occurred from October 4, 1989 through January 5, 1990 (93 days). The average number of eggs spawned during the spawning season per female were 2.67 billion. The first spawning occurred on the 60th day after the time of minimun water temperature $10.6^{\circ}C$. The water temperature and photoperiod at the first spawning were $13^{\circ}C$ and 14L/10D respectively It took 71 days to spawn since the photoperiod had changed from 10L/14D to 14L/10D. Spawning period can be devided into three terms. The first term was continued for 30 days from the beginning of the spawning. The second term for 41 days was the major spawning period followed by the third term, the final period of the spawning, for 22 days. The percentage of average fertilization rate of the eggs in the first, second and third spawning terms were $37.4{\%},\;54.1\%\;and\;19.6\%$, respectively. Feeding rate was increased in the maturing period but, decreased in the spawing period. During the final spawning period, the abrubt decreasing of the feeding occurred again.
1989년 6월 1일부터 1990년 1월 5일까지 189일간 수온과 광주기를 조절하여 넙치의 산란을 유도한 결과를 요약하면 다음과 같다. 수온 조절에 의한 최초의 산란은 최저수온 $10.6^{\circ}C$ 설정후 수온 $13^{\circ}C$ 전후인 60일 만에 산란이 시작되었고, 자연수의 수온을 낮추기 시작한 때로 부터는 76일이 소요되었다. 한편 광주기 조절에 의한 산란은 수온 $13^{\circ}C$ 전후에서 광주기가 10L/14D로 될 때부터 장일처리를 시작하여 14L/10D로 전환되는 시기에 산란이 이루어졌으며, 장일처리개시일로부터는 71일이 소요되었다. 전 산란기간은 94일이었으며, 그 중 산란이 이루어진 일수는 69일이었다. 산란기간중 1일 최대 산란양은 $133.2{\times}10^4$입 이었으며, 1마리의 평균 산란양은 $267.1{\times}10^4$입이었다. 산란 기간은 산란 전기 30일, 산란중기 41일, 산란후기 23일의 3단계로 구분되었다. 총산란양에 대한 부상란 수와 수정률은 서로 비예하는 경향이었고, 평균 수정률은 중기가 $54.1{\%}$로 가장 좋았고, 전기 $37.4{\%}$, 후기 $19.6{\%}$ 순이었으며, 전체 평균은 $44.4{\%}$였다. 한편, 사료섭식량과 산란과의 관계는 성숙이 진행되는 시간에는 섭식량이 증가하다가 산란개시시부터는 급격히 감소하였으며, 산란 종료시에는 더욱 감소하는 경향을 나타내었다.
(Dept. of Aquaculture, National Fisheries University)