Morphological Aspects of the Development of Swimming and Feeding Functions in Larval Scomber japonicus

Abstract

Developmental sequences of morphological characters concerned with swimming and feeding functions are described for Scomber japonicus, and their implication in the functional development is discussed. Finfold larvae of 5.00 mm SL and smaller swim by a somewhat strong tail beat propulsion and feed by a widely opened mouth at the anterior end of the body. The formation of the caudal fin, at the size of between 5.00 and 7.00 mm SL, is earlier than other fins; this suggests that the caudal fin plays a major role in forward propulsion in S. japonicus larvae. At almost the same time, jaw and pharyngeal teeth begin to develop, and an increase in the number of the pharyngeal teeth occurs at about 7.00 mm SL. After that, both the swimming and feeding abilities develop with rapid acceleration. Both abilities may be acquired almost completely at about 10.00 mm SL through the formation of the fins other than the caudal one for swimming and through the development of jaw elements for feeding. From these observations, the following three stages are recognized, though a bit daringly, in larval S. japonicus: 1) larvae less than 5.00 mm SL, 2) those at the size range between 5.00 and 10.00 mm SL, and 3) those larger than 10.00 mm SL. It should be noted, on the other hand, that the larval stage of S. japonicus is not divided sharply on the basis of the development of the swimming and feeding abilities, since the development is seriate and the abilities increase exponentially with larval growth. © 1984, The Japanese Society of Fisheries Science. All rights reserved.