Early Development of Fin-supports and Fin-rays in the Milkfish Chanos chanos

Abstract

Abstract Development of fin-supports and fin-rays was observed in larval and juvenile Chanos chanos. Chondrification of the caudal complex started at 4.70mm SL. Ossification of the caudal elements started at 7.80mm SL and was nearly completed at about 30mm SL. Carti-laginous fusion of caudal elements, which occurs in hypurals of higher teleostean fishes but is not seen in lower teleosts, was observed between the neural arch of the preural centrum 1 and that of the ural centrum 1 via a small cartilage bridging the distal tips of the two arches. Caudal fin-rays began to develop at 6.60mm SL, and an adult complement, of principal rays was attained at 7.35mm SL. Dorsal and anal pterygiophore elements were first evident at 6.70mm and 6.65mm SL, respectively. All proximal radials were formed at 8.15mm SL in both fins. Formation of dorsal and anal fin-rays started simultaneously at 8.60mm SL, and adult fin-ray complements were attained at 10.00mm and 10.70mm SL, respectively. In the pectoral fin, the cleithrum, coraco-scapular cartilage and blade-like cartilage (fin plate) had already been formed at 4.65mm SL. The mesocoracoid was observed to originate from the coraco-scapular cartilage and become detached from it in the course of ossification. Pectoral fin-ray formation started at 13.80mm SL and was completed in number of rays at 20.00mm SL. In the pelvic fin, the basipterygium was first evident at 13.00mm SL. Pelvic fin-rays appeared at 13.80mm SL and attained their adult count at 17.15mm SL.