Fig. 10. Remodeling of the larval flounder pectoral fin during spontaneous metamorphosis and with altered thyroid status. Changes in fin morphology that normally occur from 20 to 30 d.p.f. (A-G) can be induced with exogenous thyroid hormone treatment from 7-11 d.p.f. (H-J), or inhibited by chemical ablation of thyroid hormone with methimazol (0.1 mol l^-1) for 6 weeks after pre-metamorphosis (K). Thyroid hormone induction (100 nmol l^-1 T3) for 1 week following 6 weeks of methimazol treatment transforms the enlarged larval pectoral fin into the juvenile form (L). A juvenile bilaterally symmetric variant (60 d.p.f.) has a normally remodeled pectoral fin (M). (A-M) Bone (Alizarin Red) and cartilage (Alcian Blue) processed tissues. Late pre-metamorphosis (A), late pro-metamorphosis (B), early metamorphic climax (C), mid-climax (D), late climax (E), juvenile (F), sub-adult (G). Untreated early pre-metamorphosis (H), 3 day T3-treated (I), 4 day T3-treated (J). fs, foramen scapulae; mdz, zone of matrix decomposition; pop, postcoracoid process; pr, proximal radial; prp, precoracoid process; sco, scapulocoracoid; mr, marginal rays. Bars, 0.2 mm (in A, for A-J), 0.2 mm (in K, for K-M).