MONETTE, Michelle/Y*; MCCORMICK, Stephen/D; Univ. of Massachusetts, Amherst; Conte Anadromous Fish Research Center, USGS: Effects of short-term, sub-lethal acid/aluminum exposure on seawater tolerance and endocrinology of Atlantic salmon smolts

The acidification of rivers and streams, and the resulting elevated concentrations of dissolved aluminum (Al) have toxic effects on fish, including the disruption of ionoregulatory ability. Atlantic salmon smolts may be particularly vulnerable to this disturbance, for it is critical that they develop sufficient salinity tolerance to survive downstream migration and seawater entry. We examined whether short-term, sub-lethal acid/Al exposure would affect the salinity tolerance and the underlying endocrine mechanisms of Atlantic salmon smolts. We assigned replicate tanks to either control (pH 6.5-6.9, 0&microg/l Al) or treatment (pH 5.3-6.0 and 200&microg/l total Al) conditions, and exposed fish for 2 and 5 days. Fish were sampled for physiological parameters both in freshwater, and after a 24 h seawater challenge test. Gill Na⁺/K⁺ ATPase activity was decreased in all treatment groups relative to controls. Acid/Al exposure did not affect plasma ions in fresh water, but did result in higher plasma chloride after seawater exposure. Plasma glucose was elevated in treatment groups sampled in freshwater after both 2 and 5 days of exposure to acid/Al, indicating a stress response. However, plasma cortisol levels of treated fish were not elevated relative to controls. Short-term, sublethal acid/Al exposure compromises the salinity tolerance of Atlantic salmon smolts in part, by decreasing Na⁺/K⁺ ATPase activity thereby rendering smolts less capable at salt secretion. Further analyses include determination of plasma T3, T4, IGF-I and GH, as well as, immunocytochemistry for examining and quantifying chloride cell number and function.