RA requirement in pectoral fins after 28 hpf. (A-C) Alcian Blue stains of larval pectoral fin and girdle at 6 (A,B) and 4,5 dpf (C). Treatment with 10 µM DEAB from 10-17 hpf inhibits formation of the scapulocoracoid (sco) (B), and from 28-50 hpf affects differentiation in the proximal skeletal elements of the pectoral girdle (C). (D-G) In situ hybridizations of pectoral fins at 50 hpf; differentiation of the fin mesenchyme (D,E), appendicular muscles (F) and apical fold (G) appear unchanged upon treatment with 10 µM DEAB. cl, cleithrum; ed, endoskeletal disc.