1 NOVEMBER 1999
A.M. Schreiber, J.L. Specker-1999
Journal of Fish Biology, 55: 148-157
Abstract:
At the end of premetamorphosis, summer flounder Paralichthys dentatus larvae had 84.1% whole-body water content (WBW), which decreased to the lowest levels (81.5%) at the start of metamorphic climax (MC). During mid- and late MC, %WBW was slightly higher (82.1%) then returned to the lowest levels at the juvenile stage. In fish treated with thyroxine (T4-Na salt, 100 ng/ml) beginning at premetamorphosis, %WBW never differed from controls of the same age throughout metamorphosis, despite an earlier start of metamorphic climax and transitional settling behaviour. This suggests that thyroid hormones do not mediate the drop in %WBW which accompanies natural metamorhposis. Thiourea (TU, 30 micro g/ml) treatment of fish over the same period induced a developmental stasis in early MC which was accompanied by initially higher %WBW than controls at 33 days post-hatch, followed by a progressive decrease to abnormally low %WBW by 42 and 45 days post-hatch. Since concurrent treatment with TU+T4 rescued the fish from both the TU-induced developmental stasis and abnormally low %WBW, these findings suggest that thyroid hormones, or thyroid hormone-mediated developmental progression, are necessary for regulating %WBW.
(Department of Biological Science, University of Rhode Island, Kingston, RI 02881, USA, e-mail of J.L. Specker: jspecker@gso.uri.edu; article no. jfbi.1999.0981, available online at http://www.idealibrary.com)