Morphometric Effects of Low pH and Limed Water on the Gills of Atlantic Salmon (Salmo salar)

Abstract

Gills from adult Atlantic salmon held in water from an acid river (Westfield River, Queens County, Nova Scotia; mean pH 4.8) were compared to gills from fish held in the same water treated with limestone (mean pH 5.5) and gills from fish held in a nearby control river (Medway River; mean 5.4). Morphometric analysis showed that fish held in the acidic water had more gill chloride cells and mucous cells than those held in the limed water or the control river. The difference in chloride cell number was due to increased numbers of the cells on the primary lamellar epithelium; numbers of cells on the secondary lamellae did not increase with acid exposure. Male fish were found to have more chloride cells on their secondary lamellae than female fish. Chloride cells were larger and more nearly spherical in shape in the fish exposed to low pH water. The liming treatment was partially effective in preventing changes in gill histology. Changes in size, shape, and number of chloride cells probably represent a response of increasing ionic uptake to offset the losses of ions occurring during low pH stress.