The development of the paired fins in the Zebrafish (Danio rerio)

In the present study, we describe the structure and normal development of t he zebrafish (Danio rerio) paired fins. Particularly, we focus on the struc ture of the apical epidermis and on endoskeletal morphogenesis. Endoskeleta l development proceeds differently in the pectoral and pelvic fins. Whereas in both fins major parts of the endoskeletal girdle develop within the fin bud mesenchyme, the pattern of chondrogenic condensations observed in the pelvic fins directly reflects the adult endoskeletal pattern. In the pector al fin, a morphogenetic detour is taken via a functional larval endoskeleto n, the endoskeletal disc. It arises in the fin bud mesenchyme from a chondr ogenic anlage common with the girdle. The disc chondrifies and represents t he functional endoskeleton of the larval pectoral fin. The pectoral fin end oskeleton is expanded as well as restructured during larval stages in a pro cess which involves decomposition of cartilage matrix in the endoskeletal d isc. Our comparisons of apical fold morphology with reports on other teleos ts and tetrapod apical ridges show them to be homologous on the structural level. Comparisons of endoskeletal development of the zebrafish with report s on teleosts, actinopterygians and chondrichthyans show that endoskeletal morphogenesis in the zebrafish pectoral fin follows a morphogenetic process which is widespread among actinopterygians. (C) 1998 Elsevier Science Irel and Ltd. All rights reserved.