Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout. 1: Iono-regulatory disturbance and metabolic costs

The relationships among growth, feeding behaviour, ion regulation, swimming performance and oxygen consumption in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal Levels of waterborne Cd (3 mu g.l(-1)), Cu (75 mu g.l(-1)) or Zn (250 mu g.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8). A pattern of dis turbance, recovery and stabilization was evident for all three metal exposu res, although the degree of disturbance, specific response and time course of events varied. Growth was unaffected by any of the metals under a regime of satiation feeding but appetite was increased and decreased in Cu- and C d-exposed trout respectively. Critical swimming speed was significantly low ered in fish chronically exposed to Cu, an effect associated with elevated O-2 consumption rate at higher swimming speeds. Branchial Na+/K+ ATPase act ivity was elevated in Cu-exposed fish but not in Cd-exposed trout. Disrupti on of carcass Na+ and Ca2+ balance was evident within 2 days of exposure to either Cd, Cu or Zn, with subsequent recovery to control levels. The loss of Ca2+ in trout exposed to waterborne Cd persisted longest, and recovery t ook approximately a month. The physiological response of trout to chronic C u exposure involves mechanisms that result in an associated metabolic cost. In comparison, Cd is neither a loading nor a limiting stress and acclimati on to chronic Cd-exposure does not appear to involve a long term metabolic cost. (C) 2000 Elsevier Science B.V. All rights reserved.