Temperature and KClO(4)-induced metamorphosis in the sea lamprey (Petromyzon marinus)

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 (treated) or without (untreated) the presence of potassium perchlorate (KClO4). After 23 weeks, larvae were examined for signs of metamorphosis and serum samples were collected to assay thyroxine (T4) and 3,5,3'-triiodothyronine (T3) concentrations. Water temperature did not significantly affect serum T4 or T3 concentrations in untreated larvae and no metamorphosis occurred in these groups. Serum T4 concentrations were not significantly different between the two temperature groups treated with KClO4. However, serum T3 concentrations were significantly higher in the cold water, KClO4-treated larvae (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 T4 and T3 concentrations which were 66 and 95% lower, respectively, than untreated larvae in warm water. Despite having significantly lower serum T4 and T3 concentrations (73 and 80%, respectively) than untreated cold water larvae, metamorphosis was not observed in cold water, KClO4-treated larvae. The results of this study indicate that warm water is a requirement for the successful induction of metamorphosis with KClO4, and provide further evidence of water temperature as an important factor in the metamorphosis of lampreys.