Description of larval and juvenile yellowtail damselfish, Microspathodon chrysurus, Pomacentridae, and their osteological development
Abstract:Eggs were collected from nests of yellowtail damselfish, Microspathodon chrysurus, on a south Florida reef and hatched in the laboratory. Hatched larvae were reared, with some killed and preserved at time intervals. A series of 109 larvae and juveniles 2.0 mm NL–19.8 mm SL (3 to 79 days old) were measured for morphometric changes and examined for pigment development. Ninety of these laboratory-reared larvae (2.1 mm NL to 19.8 mm SL) and three wild-caught juvenile and adults (54.4 to 116 mm SL) were cleared and stained to study osteological development.
Larvae of M. chrysurus can be distinguished from other known damselfish larvae by their large pigmented pectoral fin and by a number of large melanophores over the hind brain and on the dorsal and ventral tail margin. Ré (1980) described early larvae of Abudefduf luridus, which are strikingly similar to the larvae of M. chrysurus.
Osteological development of the vertebral column and ribs, the paired and unpaired fins and their supports, the hyoid arch, the branchial skeleton and the opercular series were studied. Cartilaginous neural arches and spines first appeared anteriorly on the notochord; addition was in a posterior direction. Cartilaginous hypurals appeared before all neural and haemal arches and spines had developed. Notochord flexion started in a 3.7 mm NL 16-day-old larva. Pleural ribs first developed as cartilage and then ossified, whereas epipleural ribs originated directly from ossification of connective tissue. Four or five anterior haemal arches of the caudal centra supported epipleural ribs. The vertebral column ossified from anterior to posterior. The coracoid bone of the pectoral girdle had one or two foramina, a feature not observed in perciforms except pomacentrids. In M. chrysurus, the second dorsal and anal fins and supports probably started development before the first dorsal fin. There were three predorsal bones, and the first dorsal pterygiophore supported two fin spines. The first anal pterygiophore supported two spines and one ray. Middle radials were absent in the dorsal and anal fin supports, but one stay was associated with the posteriormost pterygiophore of both fins. In the caudal complex only one uroneural developed, which fused with the urostyle forming a neural canal. Principal caudal rays were 8+7 compared to the most common perciform count of 9+8. The ceratohyal bone of the hyoid arch had the primitive beryciform foramen, and the fifth ceratobranchials fused during ontogeny forming the lower pharyngeal jaw. Recently, the pomacentrids have been removed from the percoids and placed with the labroids. Our findings support this placement because of the fused fifth ceratobranchials and the reduced principal caudal ray count.
Document Type: Research Article
Publication date: March 1, 1987
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