Effects of ocean warming on the blood physiology of the Polar cod, Boreogadus saida

Anthropogenic activities disturb the global ecosystem equilibrium. In the atmosphere, greenhouse gases such as CO2 contribute to global warming, which on the one hand also has an impact on the ocean temperature. On the other hand, a greater concentration of atmospheric CO2 (PCO2) leads to an increased diffusion of CO2 into the ocean. In water, CO2 reacts and modifies oceans chemistry by decreasing pH; known as ocean acidification. Fish have a powerful ion regulatory system and react to pH modifications by active uptake of bicarbonate ions. However, this compensation modifies the composition of internal fluids and is likely to change the physiological equilibrium. This study aimed to assess the impact of a long term exposition (4 months) at different conditions of T°C and PCO2 on the oxygen carrying capacity of the hemoglobin (Hb) of an Arctic fish, the Polar cod (Boreogadus saida). Thus, Oxygen Equilibrium Curves (OECs) of Hb saturation against pH were measured on blood of acclimated fish using a modified diffusion chamber. A relative normalized quantification of RNA of each Hb sub-unit isoforms present in spleen and blood was performed using quantitative PCR (qPCR). The analysis of the OECs revealed no significant differences between the different treatments, fish compensated and managed to maintain similar oxygen binding properties whichever environment they are in. On the molecular level, there is a change in the proportions of Hb sub-units, indicating a modification of the Hb isoform composition to keep the blood’s level of performance