Thresholds for short-term acid and aluminum impacts on Atlantic salmon smolts

• Published in: Aquaculture 2012-09, Vol.362-363, p.224-231
• Main Authors: McCormick, Stephen D., Lerner, Darren T., Regish, Amy M., O'Dea, Michael F., Monette, Michelle Y.
• Format: Article
• Language: English
• Subjects: acid treatment; Acidification; acids; Aluminum; Aquaculture; Atlantic salmon; blood glucose; chlorides; freshwater; gills; hematocrit; larvae; Marine; Mortality; Na+/K+-ATPase; Osmoregulation; physiological response; Plasma; Salmo salar; Salmon; Seawater; smolts; Stress
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2011.07.001

Although the negative effects of acid and aluminum (Al) on smolt development have been known for some time, the thresholds for impact of short-term exposure of several days that may occur during episodic acidification have not been systematically examined. In order to determine the levels of acid and Al that impact juvenile Atlantic salmon, smolts and yolk-sac larvae were exposed to three pH levels (6.0, 5.7, and 5.3) and four added Al levels (0, 40, 80 and 175μg/L total Al) for 48h. Following this treatment, 10 smolts were sampled in freshwater and another 10 were subjected to a 24h seawater challenge (35ppt). Survival of yolk-sac larvae was >96% in all acid and Al treatments. All smolts died within 48h at pH 5.3, 175μgL−1 Al. There were some mortalities in freshwater at pH 5.3, 80μgL−1 Al and pH 5.7, 175μgL−1 Al, and further mortalities when these fish were transferred to seawater. Mortalities in these groups were associated with decreased plasma chloride in freshwater and higher plasma chloride in seawater, indicating that these smolts had lost seawater tolerance. Gill Na+/K+-ATPase (NKA) activity decreased at pH 5.7, 175μgL−1 Al in freshwater, and further decreases were observed at more moderate pH and Al exposures after transfer to seawater. Hematocrit and plasma glucose were the most sensitive physiological responses, increasing at all Al treatments at pH 5.7 and 5.3 in freshwater. There was no detectable increase in gill Al levels at pH 6.0 with added Al, whereas substantial increases in gill Al were observed in all added Al groups at pH 5.7 and 5.3. Our results demonstrate a critical interaction between acid and Al in their effects on smolts, and that episodic acidification events will negatively impact smolt survival in freshwater and after seawater entry.