STUDIES ON THE DEVELOPMENT OF THE NEURAL CREST IN SOME FISHES

Abstract

In the present work, the development of the neural crest cells in seven developmental stages (0.7, 1.0; 1.5; 2.0; 3.0; 4.2 and 6.0 mm total length) of the teleost fish, Xiphophorus he/leri is studied and compared with other vertebrates. Moreover, three developmental stages (3.0, 4.2 and 6.0 mm total length) of the swordtail - platyfish hybrids [used as melanoma - bearing fish] are studied also to show the fom1ation of melanoma. The study is based on photomicrographs from stained serial paraffin transverse sections (5-7 ).l in thickness) through the head and trunk regions of the studied specimens. Scanning electron micrographs of some specimens were also used. In the morphological description, the site, time of segregation and mi o,'ratory pathways of the neural crest cells have been explained. Moreover, the changes in the distribution of the extracellular matrix , components;collagen,neutral polysaccharides, non - sulfated and sulfated glycosaminoglycans during the migration of the neural crest cells, their differentiation and the formation of the melanoma are also considered. The study of the development of the neural crest cells of Xiphophorus hel!eri revealed the following results : 1- • The neural crest cells are recognized early at the dorso-lateral sides of the neural keel or the brain.