Cadmium acclimation and hormesis in Fundulus heteroclitus during fin regeneration.

We have previously demonstrated that exposure to cadmium at 0.1 and 0.5 mg/liter will retard the rate of fin regeneration in Fundulus heteroclitus. Since there is a body of literature indicating that preexposure to low levels of metals may increase tolerance during subsequent exposure, these experiments were designed to investigate the effects of preexposure to cadmium, using fin regeneration as the parameter of effect. Fish were exposed for 1 week to 0, 0.01, or 0.05 mg/liter Cd. Following this preexposure, the lower third of the caudal fin was amputated, and regrowth of the fins measured by ocular micrometer twice weekly for 2 weeks. During regeneration fish were maintained in either clean water (25% S, 23-25 degrees C) or in water with 0.1 mg/liter Cd. Fish newly placed in Cd (C----0.1 Cd) regenerated at the slowest rate, while the 0.01----0.1 Cd group approached the growth of control fish regenerating in clean water, indicating a protective effect or acclimation brought about by the preexposure. The 0.05----0.1 Cd group regenerated even more rapidly than controls, a phenomenon which has been termed "hormesis" and is believed to be due to an overcompensation by homeostatic regulatory mechanisms. In a second set of experiments in which regeneration took place in 0.5 mg/liter rather than 0.1 mg/liter, a protective effect of preexposure was again seen, but no hormesis was observed. Uptake data indicated that preexposed groups took up less Cd than the groups not preexposed.