Spawning of Japanese flounder I'arul~c:Wr,ys oli~x~ceus in captivity was studied at ambient temperature and photo period in one spawning season. The broodstock consisted of five groups of one female and two males each. The spawning lasted 113 days from February 18 to June 10 during which temperature ranged from 9.1 to 19.8"C. The spawning period and the date of first spawning differed among females. The proportion of viable eggs collected during the spawning season varied among females from 6.6

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... to 29.3%. Mean egg diameter ranged from 0.757 to 0.986 mm and tended to decline during the spawning season. Egg diameter was negatively correlated with the time from the commencement of spawning and the water temperature at spawning.