Variations in egg qualities of the Japanese whiting, Sillago japonica, in the spawning season
1986
Oozeki, Y. | Hirano, R. (Tokyo Univ., Tokyo (Japan). Dept. of Fisheries)
Changes in the egg quality of the Japanese whiting, a multiple-spawning fish, were examined throughout its spawning season. Fertilization and hatching rates were constantly high and the optimum temperature and salinity for hatching (26.0 deg C, 32.5 ppt) did not vary much. Oxygen consumption was constant at each developmental stage and linearly increased as egg development progressed. Eggs were damaged by exposure to temperatures higher than 28 deg C for 15 min. The thermal tolerance of eggs varied at each development stage. High sensitivity to temperature shock was observed at two periods, from fertilization to blastula and from middle gastrula to formation of optic vesicles. During the latter period, TL50, defined as the minimum shock temperature after which 50% eggs hatched normally, was observed to be higher in the peak spawning period than in the final spawning period. The decrease of TL50 in the final spawning period agreed well with the survival activity of starved larvae which decreased in the same period.
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