Mortality and physiological stress of year-classes of landlocked and migratory Atlantic salmon, brown trout and brook trout in acidic aluminium-rich soft water

Abstract

Physiological stress, measured as changes in plasma chloride, and mortality were measured on different year-classes of landlocked and migratory Atlantic salmon, two strains of brown trout, and brook trout, in a flow-through system with acidic Al-rich soft water. The oldest year-classes of salmon were smolts. Water from Lake Byglandsfjord (pH = 5.9), was enriched 1 th inorganic Al (as AlCl₃) and H₂SO₄ to pH = 5.1, total Al = 225 ug L⁻¹ , and labile Al = 135 ug L⁻¹ . As a reference, lake water was limed by means of a shellsanj filter to pH = 6.2, increasing Ca-concentration from 1.0 to 1.5 mg L⁻¹. During the 83 hr experiment, neither mortality nor physiological stress occurred in any species or year-class in the limed water. In the acid water, no mortality occurred on any stage of brown trout or brook trout. Among the migratory and landlocked salmon, however, 5% of the alevins died after 49 and 70 hr, respectively. All smolts of both the landlocked and the migratory salmon died after 83 and 35 hr, respectively, the co responding loss rate of plasma chloride was −0.76 and −1.26 meq Cl hr⁻¹. Brook trout, however, increased plasma ion concentration during the experimental period, and hence showed no stress.