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

Larval sea lampreys (Petromyzon marinus) were exposed to either a warm (18 degree C) or a cold (3 degree C) water temperature and either with (treated) or without (untreated) the presence of potassium perchlorate (KClO sub(4)). After 23 weeks, larvae were examined for signs of metamorphosis and serum samples were collected to assay thyroxine (T sub(4)) and 3,5,3'-triiodothyronine (T sub(3)) concentrations. Water temperature did not significantly affect serum T sub(4) or T sub(3) concentrations in untreated larvae and no metamorphosis occurred in these groups. Serum T sub(4) concentrations were not significantly different between the two temperature groups treated with KClO sub(4). However, serum T sub(3) concentrations were significantly higher in the cold water, KClO sub(4)-treated larvae (5.4 nmol/l) than in the warm water, KClO sub(4)-treated larvae (1.2 nmol/l). KClO sub(4) treatment at a warm water temperature induced metamorphosis in all larvae and resulted in serum T sub(4) and T sub(3) concentrations which were 66 and 95% lower, respectively, than untreated larvae in warm water. Despite having significantly lower serum T sub(4) and T sub(3) concentrations (73 and 80%, respectively) than untreated cold water larvae, metamorphosis was not observed in cold water, KClO sub(4)-treated larvae. The results of this study indicate that warm water is a requirement for the successful induction of metamorphosis with KClO sub(4), and provide further evidence of water temperature as an important factor in the metamorphosis of lampreys.