The effects of aluminum and acid on the gill morphology in rainbow trout,Salmo gairdneii

Synopsis The objective was to determine the effects of acid and aluminum in acidified hard and soft water on the histology and morphometry of rainbow trout gills, and to determine relevant toxicity indicators within the gill tissue. Acid and aluminum promoted measurable primary epithelial hyperplasia which proved to be a reliable biological indicator of acid and aluminum contamination and possibly of some predictive value. Low levels of aluminum and acid resulted in hypertrophied chloride cells, suggesting a role in adapting to the contaminants. High concentrations of aluminum (>10 molI^-1) caused chloride cell necrosis and consequently a decline in cell numbers over time. Aluminum precipitates accumulating within the chloride cell cytoplasm probably lead to impaired function prior to cell degeneration. The morphological alterations resulted in a decrease in water space between secondary lamellae (up to 40% within 14 d) which may reduce the efficiency of gas exchange. Twice the aluminum was required in hard water to elicit a similar soft water tissue response. Pathological changes were more severe with aluminum at pH 5.2 than at pH 4.7; results of aluminum speciation suggest that both labile and non-labile fractions are responsible for the induction of gill lesions. Low levels of aluminum may protect fish from the effects of high hydrogen ion concentration.