Physiological effects of sublethal acid exposure in juvenile rainbow trout on a limited or unlimited ration during a simulated global warming scenario.

Abstract

Changes in the physiology and cost of living of fish were studied during exposure to simulated global warming and environmental acidification, alone and in combination. Trout were exposed to slightly elevated water temperatures (+2 degrees C), in the presence and absence of sublethal acidity (pH 5.2) in synthetic softwater for 90 d (8 degrees - 12 degrees C). Fish were either fed to satiation (ca. 1%-3% of their wet-body weight daily) or fed 1% of their wet-body weight once every 4 d. Satiation-fed fish exposed to sublethal pH showed no ionoregulatory disturbances but exhibited increased appetites and growth compared to fish in control pH waters. In contrast, fish maintained on a limited ration did not grow and showed typical ionoregulatory responses to acid stress, with lower whole-body Na+ and Cl- concentrations and greater mortality. Detrimental effects were greater in the global warming scenario (+2 degrees C). Overall, a slight temperature increase and sublethal pH increased the cost of living as determined by increased food consumption in satiation-fed fish and greater mortalities in fish maintained on a limited ration. Most important, these findings suggest that fish given sufficient food can compensate for increased energy expenditure or difficulties in maintaining ion balance associated with low pH exposure.