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.