1 online resource (59 unnumbered pages) : illustrations (some colour), charts (some colour), graphs (some colour)Includes abstract and appendices.Includes bibliographical references (unnumbered pages 45-50).Endochondral ossification is a bone developing process in which a cartilaginous template gets replaced by bone. Zebrafish, Danio rerio, are teleost fish that undergo this process throughout their skeletons. This thesis is focussed on their tail bones, specifically within the hypurals and parhypural of the caudal fin. The morphological changes in the cells of the hypurals and parhypural during ossification have not been recorded so the aim of this study is to investigate these changes taking a histological approach. To determine the morphological cellular changes Hall Brunt’s Quadruple staining was used to stain the bone and cartilage within zebrafish sized 4 to 9 mm standard length. Changes within the chondrocytes were measured and descriptions of the amount of ossification were made. It was found that all five hypurals and the parhypural begin ossifying around 5.0 mm SL, while the chondrocytes underwent hypertrophy by 7.0 mm SL there was a lower percentage of hypertrophied chondrocytes in 8.0 – 9.0 mm SL specimens for hypurals 2 and 3. Hypural 2 and 3 were the elements primarily focused on, that had an increase in total hypural length (µm). These results suggest that the hypurals share features of
both endochondral and perichondral ossification. Further studies are needed to further understand ossification within the zebrafish caudal fin
