Growth and nephrocalcinosis for Atlantic salmon (Salmo salar L.) post-smolt exposed to elevated carbon dioxide partial pressures

Atlantic salmon (Salmo salar L.) post-smolt were reared at six different water CO2 partial pressures (0.6 control, 2.6, 5.5, 8.0, 10.4 and 11.6mmHg) in duplicate 500L tanks for 12weeks in 34‰ sea water at 10°C. Weight samplings divided the experiment into four periods (Periods I–IV). Plasma chloride concentration decreased linearly with increasing CO2 partial pressure in the water and the changes lasted during the four periods (p<0.05). During Period I and II, polynomial models described the significant relationship between PCO2 and specific growth rate (p<0.05). For both these periods, SGR declined between 8 and 10mmHg. No significant relationship between PCO2 and SGR was found during period III (p>0.05), however during period IV SGR decreased linearly as a function of PCO2 in the range 0.6–12mmHg (p<0.05). Condition factor decreased linearly with increasing CO2 concentration on day 19, 36, 65 and 77 (p<0.05), representing all four periods. Nephrocalcinosis was not observed in the control group, in the low group or in the medium group (medians in the range 0.6–5.5mmHg, which corresponds to 2–15mgL−1) at the end of the experiment. At the three highest PCO2 levels (medians in the range 8.0–11.6mmHg or about 21–30mgL−1), 9 of 26 fish (34%) developed nephrocalcinosis (p<0.05).