MORPHOGENESIS IN HATCHERY-REARED LARVAE OF THE BLACK ROCKFISH, SEBASTES SCHLEGELI, AND ITS RELATIONSHIP TO THE DEVELOPMENT OF SWIMMING AND FEEDING FUNCTIONS

The developmental sequence of morphological characteristics related to swimming and feeding functions was investigated in hatchery-reared la rvae and juveniles of Sebastes schlegeli, a viviparous scorpaenid. The fish were extruded at an early larval stage, when the mean body size was 6.23 mm TL. Fin-ray rudiments became visible at 9.0 mm TL in the d orsal and anal fins, at 8.0 mm TL in the pectoral and pelvic fins and 6.0 mm TL (size at extrusion) in the caudal fin. Completion of segment ation of soft rays in the dorsal and anal fins was attained by 14 mm T L and in all fins by 17 mm TL. Branching of soft rays in the respectiv e fins started and was completed considerably later than the completio n of segmentation, as well as ossification of the fin-supports. Morpho logical transformation from larva to juvenile was apparently completed by about 17 mm TL. Although the completion of basic juvenile structur es was attained by transformation at that body size, succeeding morpho logical changes occurred between 17 mm and 32 mm TL. Newly-extruded la rvae possessed one or two teeth on the lower pharyngeal and pharyngobr anchials 3 and 4, but lacked premaxillary, dentary, palatine and prevo mer teeth. The fish attained full development of gill rakers and gill teeth by 15 mm TL, the upper and lower pharyngeal teeth subsequently d eveloping into a toothplate. Development of the premaxillary, dentary and palatine teeth was completed at about 30 mm TL, by which time loop formation of the digestive canal and the number of pyloric caeca had attained the adult condition. The developmental sequence of swimming a nd feeding functions during larval and early juvenile periods appeared to proceed from primitive functions to advanced or complex ones, from the ability to produce propulsive force to that of swimming with high maneuverability and from development of the irreducible minimum funct ion of passing food into the stomach to the ability to actively captur e prey via passive food acquisition with the gill rakers and gill teet h. The relationship of morphological development to the behavior and f eeding activity of artificially-produce hatchlings is also discussed.