Development, survival, and structural alterations of embryos and alevins of Atlantic salmon, Salmo salar L., continuously exposed to alkaline levels of pH, from fertilization

Embryos of the Atlantic salmon, Salmo salar L., were incubated continuously from fertilization at pH 6.8 (control) and pH 9.0 and 9.5, initially at 6.7 °C but with a gradual decline in the first 5 weeks to 5.0 °C for the remaining 10 weeks of exposure. Subsequently, the alevins were maintained in these environments for 50 days after hatching. Developmental processes and hatching were not affected by these levels of pH. Percentage cumulative mortality of treated embryos, 8%, was approximately that in the controls. Alevin mortality in the control lots was 1.2 and 1.3%. At pH 9.0, cumulative mortality was 0.4%, but at pH 9.5 there was an accelerating increase to 18%, at the termination of observation.Sublethal changes in embryos were confined mostly to cell necrosis and sloughed rudimentary epidermis. Some metaplasia of the brain stem occurred at pH 9.5. Sites and intensity of alterations increased in alevins at pH 9.5, following the loss of the zona radiata. In addition to ongoing injury of epidermis, including mucous cells, deleterious alterations occurred in branchial epithelium, erythrocytes, myocardium, blood vessels of the viscera, liver, brain, and optic lenses. In general, sublethal changes caused by hydroxylions are similar to those caused by excessive hydrogen ions but are somewhat less extensive in the structures affected or in their degree of severity.