Long-term sublethal effects of carbon dioxide on Atlantic salmon smolts (Salmo salar L): ion regulation, haematology, element composition, nephrocalcinosis and growth parameters

Summary

Atlantic salmon (Salmo salar L.) smolts (mean weight 66 g) in freshwater were exposed to three replicate levels of carbon dioxide (CO2) partial pressures for 60 days in an open flow system: 2 mm Hg (6 mg l(-1); control), 5 min Hg (16 mg l(-1); medium) and 7 mm Hg (24 mg l(-1); high) at constant pH. Water temperature was 7-9 degreesC and oxygen concentration higher than 9 mg l(-1). All groups were transferred to 34 parts per thousand seawater on day 60 and kept there for 150 days. No significant differences in weight and length were found between groups during the freshwater and seawater period. While mean cellular haemoglobin (in the high group) and plasma chloride (in the medium and high group) were significantly lower than that of the control group during the freshwater period, no significant differences between groups were observed in mean haemoglobin concentration, haematocrit, or gill Na+,-K+-ATPase activity. Increased nephrocalcinosis and contents of Ca in the kidney in response to increasing water CO2 levels were observed at day 58. After 4 weeks in seawater, pH in muscle and whole body ash, Ca, P and Zn content were all significantly higher in fish exposed to elevated CO2 levels during the freshwater period. This indicates that freshwater CO2 levels affected tissue mineral content after transfer to seawater. (C) 2003 Elsevier Science B.V. All rights reserved.