Early Development of Laboratory-reared Giant Croaker, Nibea japonica

Abstract

Fertilized eggs of giant croaker Nibea japonica were obtained from reared adult fish injected with gonadotrophic hormone. Larvae and juveniles were reared for 3 months on rotifers, Artemia nauplii, Tigriopus japonicus, fish eggs and larvae, and artificial feed. Early developmental stages in giant croaker are illustrated, with special reference to morphological transformations, fin development, squamation, and development of digestive tract. The artificially fertilized eggs were 0.94±0.03 mm in mean diameter. Hatching occurred 26-29 h after fertilization at water temperatures of 22.0-23.5°C. On the 3rd day after hatching, larvae completed yolk absorption and started feeding at 3.09±0.08 mm in body length (BL). Notochord flexion started on the 11th day at 4.88±0.21 mm BL. The morphological transition from the larval to the juvenile stage occurred between 8.4 mm and 12.4 mm BL. Then all fin rays attained the adult complement. Squamation was completed at 8,4-12.9 mm BL, and rudimentary pyloric caeca appeared when the larvae transformed into juveniles, at between 8.9 mm and 13.6 mm BL. Juveniles over 30 mm BL completed the formation of adult-like digestive system. Three marked changes appeared in the relative growths at approximately 4-5 mm, 8-11 mm and 30-35 mm BL. These morphological changes corresponded to the notochord flexion, the transformations from larva to juvenile and from juvenile to young, respectively.