Long-term separate and combined effects of environmental hypercapnia and hyperoxia in Atlantic salmon (Salmo salar L.) smolts |
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Authors: | Camilla Diesen Hosfeld, Annhild Engevik, Ted Mollan, Torleif Markussen Lunde, Rune Waagb , Anne Berit Olsen, Olav Breck, Sigurd Stefansson,Sveinung Fivelstad |
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Affiliation: | Camilla Diesen Hosfeld, Annhild Engevik, Ted Mollan, Torleif Markussen Lunde, Rune Waagbø, Anne Berit Olsen, Olav Breck, Sigurd Stefansson,Sveinung Fivelstad |
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Abstract: | Atlantic salmon (Salmo salar L.) parr (mean start weight 50 g) were reared in freshwater (FW) and exposed to three levels of oxygen saturation measured in effluent water; control group (93% O2, LO2), medium (111% O2, MO2) and high (123% O2, HO2). Further three groups were exposed to similar water oxygen levels in combination with elevated carbon dioxide levels (17–18 mg L– 1 CO2), named LO2–CO2, MO2–CO2 and HO2–CO2, respectively. The experiment was run in duplicate tanks for 42 days, and the fish were subsequently transferred to the same seawater (SW) regime for 45 days for an assessment of post-smolt growth. As a consequence of the CO2 addition, tank pH levels in the FW period were reduced from 6.7 to 5.9 for the hypercapnia groups compared to for the normcapnia groups. Water temperature in FW ranged between 6.4 and 9.0 °C. Citrate was added to the water to complex labile aluminium.In the CO2 groups observed ventilation frequencies were significantly increased compared to the control (p < 0.05). This difference declined towards the end of the FW period, suggesting acclimation to elevated CO2. The degree of oxygenation appeared to contribute to the acclimation as the lowest mean ventilation frequency on day 36 was found in the HO2–CO2 group and the highest in the LO2–CO2 group. Lower plasma chloride and sodium levels were observed in the CO2 groups relative to the respective oxygenation groups during the FW period, while plasma chloride and sodium levels were normalised to equal levels for all groups after 44 days in SW. No significant differences were found among treatments for blood concentrations of red blood cells, haemoglobin, potassium and glucose during the experiment.By termination of the FW period, the HO2 group had significantly higher body weight than all other groups (p < 0.05), with specific growth rate significantly higher than the CO2 groups (p < 0.05). Further, the condition factor was significantly lower in all the CO2 groups at the end of the FW period compared to the control and normcapnia groups (p < 0.05). Although variable among replicates, occurrence of nephrocalcinosis was 10 times higher in the hypercapnia groups than in the control and normcapnia groups. Mortality was negligible (< 2.0%) during the trial, and most of the mortality occurred following SW transfer. |
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Keywords: | Hyperoxia Hypercapnia Oxygen Carbon dioxide Haematology Salmo salar L. |
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