title: Impacts of short-term acid and aluminum exposure on Atlantic salmon (Salmo salar) physiology: a direct comparison of parr and smolts.
abstract: Episodic acidification resulting in increased acidity and inorganic aluminum (Al(i)) is known to impact anadromous salmonids and has been identified as a possible cause of Atlantic salmon population decline. Sensitive life-stages such as smolts may be particularly vulnerable to impacts of short-term (days-week) acid/Al exposure, however the extent and mechanism(s) of this remain unknown. To determine if Atlantic salmon smolts are more sensitive than parr to short-term acid/Al, parr and smolts held in the same experimental tanks were exposed to control (pH 6.3-6.6, 11-37 microgl(-1) Al(i)) and acid/Al (pH 5.0-5.4, 43-68 microgl(-1) Al(i)) conditions in the lab, and impacts on ion regulation, stress response and gill Al accumulation were examined after 2 and 6 days. Parr and smolts were also held in cages for 2 and 6 days in a reference (Rock River, RR) and an acid/Al-impacted tributary (Ball Mountain Brook, BMB) of the West River in Southern Vermont. In the lab, losses in plasma Cl(-) levels occurred in both control parr and smolts as compared to fish sampled prior to the start of the study, however smolts exposed to acid/Al experienced additional losses in plasma Cl(-) levels (9-14 mM) after 2 and 6 days, and increases in plasma cortisol (4.3-fold) and glucose (2.9-fold) levels after 6 days, whereas these parameters were not significantly affected by acid/Al in parr. Gill Na(+),K(+)-ATPase (NKA) activity was not affected by acid/Al in either life-stage. Both parr and smolts held at BMB (but not RR) exhibited declines in plasma Cl(-), and increases in plasma cortisol and glucose levels; these differences were significantly greater in smolts after 2 days but similar in parr and smolts after 6 days. Gill NKA activity was reduced 45-54% in both life-stages held at BMB for 6 days compared to reference fish at RR. In both studies, exposure to acid/Al resulted in gill Al accumulation in parr and smolts, with parr exhibiting two-fold greater gill Al than smolts after 6 days. Our results indicate that smolts are more sensitive than parr to short-term acid/Al. Increased sensitivity of smolts appears to be independent of a reduction in gill NKA activity and greater gill Al accumulation. Instead, increased sensitivity of smolts is likely a result of both the acquisition of seawater tolerance while still in freshwater and heightened stress responsiveness in preparation for seawater entry and residence.
authors: Organismic and Evolutionary Biology, University of Massachusetts, 611 North Pleasant Street, Amherst, MA 01003, USA. michelle.monette@yale.edu
authors: Michelle Y
authors: MY
authors: Monette
authors: Stephen D
authors: SD
authors: McCormick
mesh_terms: D000535:Aluminum / Q000032:analysis / Q000633:toxicity*; D000818:Animals; D001786:Blood Glucose / Q000032:analysis / Q000187:drug effects; D002712:Chlorides / Q000097:blood / Q000378:metabolism; D004781:Environmental Exposure; D005618:Fresh Water / Q000032:analysis; D005880:Gills / Q000737:chemistry; D006854:Hydrocortisone / Q000097:blood; D006863:Hydrogen-Ion Concentration; D020317:Salmo salar / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D001786:Blood Glucose; D002712:Chlorides; D014874:Water Pollutants, Chemical; D000535:Aluminum; D000254:Sodium-Potassium-Exchanging ATPase; D006854:Hydrocortisone