Stress responses in Arctic char (Salvelinus alpinus L.) during hyperoxic carbon dioxide immobilization relevant to aquaculture

Abstract

Physiological responses during immobilization with hyperoxic hypercapnia were determined in cannulated Arctic char (Salvelinus alpinus) exposed for 10min to mixtures of 10% CO2 in 90% O2 (10:90) or 50% CO2 in 50% O2 (50:50). Results were compared with a previous study on the same group of char using pure CO2 under identical experimental conditions to test the hypothesis that supplemental oxygen may reduce stress and improve welfare during CO2 exposure. While all fish recovered from the two exposures, the time to loss of equilibrium with the 50:50 mixture was significantly shorter than for the 10:90 mixture (143 vs. 276s); and the time to regain equilibrium was longer (2302 vs. 963s). Hypertension and bradycardia developed with 10:90, while 50:50 resulted in tachycardia and unchanged blood pressure. Ventilation frequency and amplitude increased significantly with 10:90, whereas ventilation ceased completely with 50:50. Primary and secondary stress responses were evident during recovery in normoxia in both groups as indicated by elevated heart rate and ventilation and increased plasma cortisol. However, recovery appeared to be faster with the 10:90 mixture because ventilation amplitude and plasma cortisol levels declined more rapidly. Nonetheless, the times to loss of equilibrium recorded here with mixtures of oxygen and carbon dioxide bracket that observed previously with pure CO2. Furthermore, the increase in plasma cortisol was similar or higher in the present study suggesting that while supplemental oxygen does not markedly reduce stress or improve welfare during carbon dioxide immobilization, survival and recovery in normoxia are improved.