Spawning, eggs, larvae and juveniles of the purplish amberjak Seriola dumerili

The spawning, embryonic development, and morphological changes of the purplish amberjack Seriola dumerili were observed using specimens reared at the Aquaculture Research Laboratory of Nagasaki Prefectural Institute of Fisheries. Spawning was induced by intra-mascular injection of pituitary homogenate of the chum salmon Oncorhynchus keta and the genital hormone. Spawning occurred 36 hours after hormone treatment and 1, 400, 000 and 7, 000, 000 eggs were obtained in 1990 and 1991, respectively. The eggs were pelagic, spherical, and 1.05-1.20mm in diameter with a single oil globule of 0.22-0.28mm. The larvae hatched out 37 hours after spawning (W. T. 24.6°C). The newly hatched larvae were 2.7-3.1mm in length with 26 myotomes and a single oil globule. The yolk was mostly absorbed on the 4th day after hatching when the larvae attained 3.9mm in length and began to feed on rotifers. In the postlarval stage (6.3mm B. L.) the rudiments of ventral, dorsal, and anal fins began to develop and the vertebra was well ossified. In the juvenile stage (11.2mm B. L.) the membranous fins disappeared and fish gathered around drifting algae. Later in the juvenile stage (35.0mm B. L.) six or seven lateral bands appeared in the trunk as well as a band from the eye to the anterior part of the dorsal fin base. At a body length of 100mm, they reached the stage of young fish, while at a size of over 170mm in body length a yellow vertical stripe appeared from behind the operculum to the caudal peduncle. The smallest size of sexual maturation was thought to be about 600mm. Notochord or standard length at each growth stage was as follows: 2.7-3.9mm (yolk sac stage), 3.9-4.7mm (preflexion stage), 4.8-8.5mm (postflexion stage), 10-100mm (juvenile stage), 100-600mm (young stage), and over 600mm (adult stage).