Observations of early developments of the Antarctic krill, Euphausia superba DANA

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During two cruises of R. V. KAIYO MARU for Antarctic expeditions, raising experiments of the Antarctic krill, Euphausia superba DANA, were conducted in order to observe its early developments. The krill were collected in the Indian sector of the Antarctic Ocean by a 0-36m oblique tow using the KOC-A net on January 24,1980 and by a 0-103m oblique tow using the KYMT net on January 22,1981. Water temperature was kept at +0.4℃ throughout the 1980 experiments, and about 0.0∿-1.0℃ in 1981. The post-hatching developments toward the metanauplius stage were observed in 1980 while the cleavages of two- to 64-cell stages were observed in 1981. In 1980 only the starting time of each stage from nauplius I to metanauplius was obtained because each time range could not be examined. It took about 9.3-10.3 hours for the released eggs to start cleavage, seven days for hatching and 25 days to reach the metanauplius stage. Metanauplius was the most developed stage obtained in this study since all larvae died at this stage. The developmental rate of the eggs and larvae observed in this study was relatively slower, being about 4-9 hours for the two-cell stage, about 4 days for hatching and about 15 days for the metanauplius stage, than that found by MCWHINNIE and DENYS (Antarct. J. U. S., 13,133,1978).
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