1983 Volume 30 Issue 1 Pages 47-60
Developmental sequences of characters concerned in swimming and feeding functions were investigated in the laboratory-raised larvae of Pagrus major. The finfold of early larvae was completely separated at 6.50 mm in notochord length (NL). The vertical fins developed earlier than the paired fins; the formation of dorsal, anal and caudal fin-supports and fin-rays started by 5.90 mm NL and their principal adult complements were attained by 6.50 mm NL, whereas an adult complement of fin-rays was attained at 9.40 mm NL in the pectoral fins and not attained by 10.15 mm NL, the largest size we examined, in the pelvic fins.In the vertical fins the development of the caudal fin preceded that of the dorsal and anal fins.The flection of the notochord end started at around 5.00 mm NL and was completed at about 6.50 mm, at which the angle of flection was 40°-50°. The body became increasingly deep in relation to NL up to about 6.50 mm NL, after which the depth maintained an almost steady ratio to NL. These pat-terns of development suggest that the larvae of P. major shift their mode of swimming from less active larval movement to active caudal propulsion at sizes between 5.00 mm and 6.50 mm NL.
As for feeding-related characters, the premaxillae appeared at 4.35 mm NL and came to occupy most of the upper jaw margin as in adults at about 7.00 mm NL. The formation of teeth started earlier on the upper and lower pharyngeals than on the premaxillae and dentaries. How-ever, a more or less abrupt increase in number of teeth occurred at about 7.00 mm NL irrespec-tive of regions. Observations on these characters indicate that the larvae of Pagrus major change their mode of feeding from swallowing to biting at sizes between 5.00 mm and 7.00 mm NL.
Incorporating these findings and our observations on the behavior of larvae, three stages may be recognized according to the mode of swimming and feeding in Pagrus major larvae. They are: 1) the early stage with less active swimming and feeding by swallowing prey (to about 5.00 mm NL); 2) the transitional stage (to about 6.50-7.00 mm NL); and 3) the advanced stage with swimming by caudal propulsion and feeding by biting prey (about 6.50-7.00 mm NL and larger).
