Plasma calcium and calcitonin levels in eels fed a high calcium solution or transferred to seawater

To examine the physiological role of calcitonin (CT) in calcium homeostasis of teleosts, we compared calcium and CT levels in freshwater eels fed a high calcium-consomme solution (Ca2+: 1.25 M; 1 ml/100 g body wt) into the stomach (Experiment I), and in freshwater eels transferred from freshwater to seawater (Experiment II). In experiment I, plasma calcium and CT levels in the high calcium-treated eels rapidly increased (calcium: 2.63 mM at 0 h to 8. 50 mM at 3 h; CT: below detection level at 0 h to 1118.2 pg/ml at 3 h). Plasma calcium and CT levels in the control eels remained below detection level during the 3 h of the experiment. In experiment II, the plasma CT levels did not increase, although the plasma calcium levels increased from 3.23 mM at 0 h to 4.10 mM at 8 h. Therefore, in eels, we demonstrate a correlation between plasma CT and plasma calcium raised by dietary calcium in the consomme form, but it does not participate in the initial processes of seawater adaptation.