Cardiorespiratory adjustments to chronic environmental warming improve hypoxia tolerance in European perch (Perca fluviatilis)

Aquatic hypoxia will become increasingly prevalent in the future as a result of eutrophication combined with climate warming. While short-term warming typically constrains fish hypoxia tolerance, many fishes cope with warming by adjusting physiological traits through thermal acclimation. Yet, little is known about how such adjustments affect tolerance to hypoxia. We examined European perch (Perca fluviatilis) from the Biotest enclosure (23 degrees C, Biotest population), a unique similar to 1 km(2) ecosystem artificially warmed by cooling water from a nuclear power plant, and an adjacent reference site (16-18 degrees C, reference population). Specifically, we evaluated howacute and chronic warming affect routine oxygen consumption rate (<(M)over dot>(O2,routine)) and cardiovascular performance in acute hypoxia, alongside assessment of the thermal acclimation of the aerobic contribution to hypoxia tolerance (critical O-2 tension for <(M)over dot>(O2,routine): P-crit) and absolute hypoxia tolerance (O-2 tension at loss of equilibrium; P-LOE). Chronic adjustments (possibly across lifetime or generations) alleviated energetic costs of warming in Biotest perch by depressing <(M)over dot>(O2,routine) and cardiac output, and by increasing blood O-2 carrying capacity relative to reference perch acutely warmed to 23 degrees C. These adjustments were associated with improved maintenance of cardiovascular function and <(M)over dot>(O2,routine) in hypoxia (i.e. reduced P-crit). However, while P-crit was only partially thermally compensated in Biotest perch, they had superior absolute hypoxia tolerance (i.e. lowest P-LOE) relative to reference perch irrespective of temperature. We show that European perch can thermally adjust physiological traits to safeguard and even improve hypoxia tolerance during chronic environmental warming. This points to cautious optimism that eurythermal fish species may be resilient to the imposition of impaired hypoxia tolerance with climate warming.

Automated summary

The study found that European perch can thermally adjust physiological traits to increase tolerance to hypoxia, especially in the face of long-term climate warming. This suggests that some fish species may have a certain level of resilience to the decreased hypoxia tolerance caused by climate warming.