Expression of collagen genes in the pectoral fins of P. antarcticum , C. aceratus , G. aculeatus , and D. rerio embryos, detected by whole-mount in situ hybridization. (A-C) P. antarcticum, mid-larvae; (D-F) C. aceratus, mid-larvae; (G-I) G. aculeatus, 7 dpf; (J-L)D. rerio, 3 dpf. Images are of flat-mounted (A-C, G-L) or vibratome-sectioned (D-F) pectoral fins. Expression of col2a1 is observed in the scapulocoracoid (co) of all species (A, D, G, J). Likewise expression of col10a1 (B, E, H, K) and col1a1 (C, F, I, L) is observed in the cleithrum (cl), and col1a1 is expressed in the fin fold (ff) of all species. C. aceratus exhibits a unique pattern of col10a1 expression in the endochondral disk (ed) (E). Thus, gene expression during fin development appears to be largely conserved among these species. The tree represents the evolutionary relationship among species. Scale bars, 100 μm.