Swimming performance, whole body ions, and gill Al accumulation during acclimation to sublethal aluminium in juvenile rainbow trout (Oncorhynchus mykiss).
Juvenile rainbow trout (2-5 g) were chronically exposed (for 22 days) to acidified softwater (Ca(2+) = 25 μEq/l, pH 5.2) in the presence or absence sublethal Al (30 μg/l). Al-exposed fish (5.2/Al group) suffered 20% whole body Na(+) and Cl(-) losses and a 30% reduction in the maximum sustainable swimming speed (Ucrit) over the initial 7 days. These disturbances were approximately 2 fold greater than those observed in the fish exposed to low pH alone (5.2/0 group). However, whole body ion levels were completely restored in the 5.2/Al fish by day 22, whereas they merely stabilized at a new reduced level in the 5.2/0 group. Increased resistance to acutely lethal Al (200 μg/l at pH 5.2) was observed from day 17 onwards in the 5.2/Al fish. Despite this acclimation and recovery of whole body ions, Ucrit remained significantly lower than in the 5.2/0 group throughout. Growth on a restricted diet of 1% body wt. /day was normal in the 5.2/0 group compared with controls maintained in pH 6.5 softwater, whereas 5.2/Al fish suffered a 50% reduction in growth rate on the same diet. The 5.2/Al fish accumulated large amounts of Al on the gills, reaching an initial peak after 4 days, followed by a decline at 7 days, and a secondary rise thereafter. Therefore acclimation and recovery of whole body ionic status was not associated with a reduction in the gill Al burden. Some of the metabolic costs of acclimation to Al, namely a continued impairment of swimming speed and growth, are discussed in light of the physiological and structural changes reported to occur at the gills.
Department of Biology, McMaster University, L8S 4K1, Hamilton, Ontario, Canada.
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Wilson
C M
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Wood