Temperature and KClO4-induced metamorphosis in the sea lamprey (Petromyzonmarinus)

Larval sea lampreys (Petromyzon marinus) were exposed to either a warm (18 degrees C) or a cold (3 degrees C) water temperature and either with (treat ed) or without (untreated) the presence of potassium perchlorate (KClO4). A fter 23 weeks, larvae were examined for signs of metamorphosis and serum sa mples were collected to assay thyroxine (T-4) and 3,5,3'-triiodothyronine ( T-3) concentrations. Water temperature did not significantly affect serum T -4 or T-3 concentrations in untreated larvae and no metamorphosis occurred in these groups. Serum T-4 concentrations were not significantly different between the two temperature groups treated with KClO4. However, serum T-4 c oncentrations were significantly higher in the cold water, KClO4-treated la rvae (5.4 nmol/l) than in the warm water, KClO4-treated larvae (1.2 nmol/l) . KClO4 treatment at a warm water temperature induced metamorphosis in all larvae and resulted in serum T-4 and T-3 concentrations which were 66 and 9 5% lower, respectively, than untreated larvae in warm water. Despite having significantly lower serum T-4 and T-3 concentrations (73 and 80%, respecti vely) than untreated cold water larvae, metamorphosis was not observed in c old water, KClO4-treated larvae. The results of this study indicate that wa rm water is a requirement for the successful induction of metamorphosis wit h KClO4, and provide further evidence of water temperature as an important factor in the metamorphosis of lampreys. (C) 1999 Elsevier Science Inc. All rights reserved.