The Early Developmental Pattern of Axial Skeleton in Thamnaconus septentrionalis
[Objectives]The aim of this study was to investigate the developmental stage and ossification sequence of the axial skeleton in the early development of Thamnaconus septentrionalis,and to provide reference for seedling cultivation.[Methods]Using the Alcian Blue and Alizarin Red double staining for cartilage-bone to study the developmental pattern of the axial skeleton(skull and vertebrae)of T septentrionalis from 0-60 dah(days after hatching).[Results]The results showed that in newly hatched larvae,no apparent skeletal elements were observed in the head.At 3 dah(days after hatching),there were cranial cartilage components such as trabecula cranii,parachordal,auditory cartilage ring and ethmoid plate,as well as cartilaginous components such as Meckel's cartilage,palatoquadrate,ceratobranchial cartilage,and basibranchial cartilage.At 8 dah,the auditory cartilage ring fused into a round shape,the ends of the maxilla was connected to the palatoquadrate,and the ceratobranchial cartilage gradually shortened from anterior to the posterior.At 15 dah,the auditory cartilage ring protruded,the skeletal framework of the head became stable,the dentary and sympletic appeared,and the gill filaments were densely distributed.At 18 dah,the olfactory cartilage ring,hypohyal and epihyal cartilage appeared,Meckel's cartilage regressed,conical tooth appeared at the anterior of the upper and lower jaws.At 20 dah,the frontal and ethmoid appeared,the preopercle and premaxilla appeared and ossified.At 22 dah,the preopercle extended downward into lamellae,and the branchiostegal ray fully ossified.At 24 dah,parietal,parasphenoid,subopercle,operculum and ceratohyal appeared and ossified.At 26 dah,the head was covered with sclerosified conical scales that were fully ossified.At 33 dah,the frontal,ethmoid and taenia marginalis posterior fully ossified,the rostral elongated,subopercle and operculum fully ossified,and conical teeth changed to incisor-like.At 50 dah,all the cartilages were ossified except the gill filaments and the cranial skeleton fully ossified can be considered(Fig.2).The vertebral column of the T.septentrionalis was transparent and colorless in the first 14 dah.At 18 dah,the formation of the neural arch and haemal arch at the posterior end was observed.At 25 dah,the segmentation of the vertebral column was completed.At 28 dah,ossification of the centrum was completed.At 30 dah,the posterior articular of some centrum fused with the neural spine.At 45 dah,the intervertebral spacing decreased,and the vertebral column fully ossified(Fig.3).[Conclusion]This study clarified the developmental stages and ossification sequence of the axial skeleton elements during the early development of the T.septentrionalis,providing theoretical references for this species seedling cultivation.
Thamnaconus septentrionalisAlcian blue and Alizarin stainingLarvaeJuvenileAxial skeleton
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