Studies on early development and spawning ecology in Japanese sardine Sardinops melanostictus
2008
Matsuoka, M.(National Research Inst. of Fisheries and Environment of Inland Sea, Hatsukaichi, Hiroshima (Japan))
In the most resource period and decrease one of Japanese sardine Sardinops melanostictus, the early development and spawning ecology of Western Kyushu population were investigated, from biological aspect. Incubation and rearing experiments at temperature of 18 deg C were undertaken, using wild eggs. Total length of just hatched larvae was 3.44 mm. Fourth day-old larvae after hatching (about 5.7 mm TL) began to eat S type rotifers. 17th day-old larvae reached 9.9 mm TL on the average (range 8.50-11.95 mm), and the rudiments of the dorsal and caudal fin rays and fin-supports were partly formed. 29th day-old larvae reached 15.37 mm TL (maximum, 20.0 mm). In groups deprived of food from first-feeding stage, eighth day-old, 12th day-old and 17th day-old after hatching, most larvae could not take rotifers which were given on after three or four days. Developmental process of all cartilages and bones was described, using artificially raised and wild specimens. Changes in feeding and swimming functions were clarified from osteological side, and a developmental step forming four periods and eight phases was prescribed. The most spawning period was in March and the most GSI rate of females was over 20. From the ratio of specimens with hydrated eggs or postovulatory follicles at the regressing stage 0 (spawning day), presumptive example of the average spawning interval was calculated to be from 4 to 6 days.
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