Histopathologic changes in surficial tissues of brook trout, Salvelinusfontinalis (Mitchill), exposed to acute and chronic levels of pH

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Abstract
Fingerling brook trout, Salvelinusfontinalis (Mitchill), were subjected to acute and chronic pH stress for maximum periods of 10 000 min in a series of continuous-flow dilutions of sulphuric acid or sodium hydroxide from pH 2.2 to 10.8 at 10 and 20 °C after acclimation at 15 °C and pH 6.8. Various tissues, gill, eye, naris, integument, and alimentary tract, were examined histologically and compared with control samples kept at pH 6.8. No differences in the degree or form of tissue injury were detected between series for corresponding pH levels at 10 and 20 °C. Thresholds for tissue and cellular derangements were pH 5.2 and 9.0. Mucous cells of gills, nares, and integument exhibited progressive degrees of hypertrophy and excessive secretion of mucus with increased pH stress. Epithelial necrosis and sloughing occurred extensively on gills, corneae, and integument. At the lethal levels (pH 3.5 and 9.8), epithelial necrosis also occurred in the esophagus. No cellular injury was detected in the stomach or any part of the intestine.