Histopathological Changes in the Gills of Pearl Dace, Semotilus margarita, and Fathead Minnows, Pimephales promleas, from Experimentally Acidified Canadian Lakes

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Abstract
The gills of pearl dace form experimentally acidified Canadian ELA lakes 223 (pH 5.2) and 114 (pH 5.8) and fathead minnows from Lake 114 were examined microscopically and compared with gills from unacidified waters. The acid-exposed gills exhibited (1) hyperplastic primary lamellar epithelia, (2) diminished respiratory lamellar surface areas, (3) widened respiratory blood-water barriers, and (4) altered cellular composition and morphology, especially greater numbers of chloride (ionoregulatory) cells with and without apical pits. While little can be said about the effects of acid water on fish based on such a small sample of lakes, the present research does not contradict the views expressed by many investigators that very soft water with a low pH and toxic metal ions has a deleterious effect on gills and the physiological processes associated with them.