コショウダイの初期生活史

抄録

Early life history of the threebanded sweetlip, Plectorhynchus cinctus was studied from eggs, larvae and juveniles reared in the laboratory.Juveniles collected from the Suo Sea in the western region of the Seto Inland Sea were also studied.The artificial insemination was carried out in June and July and larvae were reared from June 25 to September 7 of 1981.
Eggs were 0.79 mm in diameter, pelagic, spherical with a single oil globule of 0.20 mm in diameter.Incubation time was 33-35.5 hours at the temperatures of 21.6-23.2°C.Length of prolarva 2 hours after hatching was 2.2 mm.By the time of yolk absorption in three days larvae grew to 2.9 mm.Transformation of larvae to the juvenile stage was completed at 9.1 mm.During early developmental stages, outstanding features included the formation of head armatures and dense pigmentation of body.Head armatures were acquired in the sequence of preopercular spines at 3.3 mm, supraorbital and upper cleithral spines at 5.5 mm, and postocular and subopercular spines at 9.1 mm.Several of these spines and the conical teeth in early juveniles were lost in the advanced specimen of 21.3 mm.In advanced larvae and juveniles melanophores were scattered over the entire surface of body except the upper parts of soft dorsal and anal fins, pectoral fin and caudal fin including caudal peduncle.This color pattern changed rapidly by physical stimuli from the uniformly black to the pale with distinct four oblique bands suggesting the potential differentiation of the typical color pattern in this species.A wild-caught juvenile, 50 mm in total length was provided with three oblique bands and several dots which were more distinct and fewer than those in the adults.In the fields, juveniles were found from early July to early August in the surf zone in the waters surveyed.