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 11.6 mm Hg) in duplicate 500 L tanks for 12 weeks 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 10 mm Hg. 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 0.6-12 mm Hg (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 0.6-5.5 mm Hg, which corresponds to 2-15 mg L− 1) at the end of the experiment. At the three highest PCO2 levels (medians in the range 8.0-11.6 mm Hg or about 21-30 mg L− 1), 9 of 26 fish (34%) developed nephrocalcinosis (p < 0.05).