METABOLIC COSTS AND PHYSIOLOGICAL CONSEQUENCES OF ACCLIMATION TO ALUMINUM IN JUVENILE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) .1. ACCLIMATION SPECIFICITY, RESTING PHYSIOLOGY, FEEDING, AND GROWTH

Juvenile rainbow trout (Oncorhynchus mykiss, 5-13 g) became acclimate (i.e., increased their resistance to lethal Al levels, 162 mug.L-1, pH 5.2) after only 5 d when exposed to sublethal Al (38 mug.L-1) in acid ified soft water (Na+ = 85, Ca2+ = 28 muEq.L-1, pH 5.2). Acclimation w as associated with reduced ionoregulatory and respiratory disturbances during lethal Al challenge and was maintained for at least 34 d. Accl imation was relatively specific to Al because no consistently improved resistance to lethal Cu (32 mug.L-1, pH 5.2) was observed. Exposure t o sublethal acid alone (pH 5.2) did not result in acclimation to letha l [H+] (pH 4.0) and caused a pronounced reduction in whole-body Na+ an d Cl-. Sublethal acid + Al resulted in a more rapid loss of ions than sublethal acid alone over the first 10 d, but both groups subsequently recovered ionoregulatory status after 34 d. Exposure to sublethal aci d alone had a negligible effect on feeding or growth. However, growth was impaired by 29% in Al-exposed trout, primarily the result of reduc ed appetite during the first 10 d. Decreased growth must be considered one of the costs of acclimation during chronic sublethal exposure to Al.