Excess post-hypoxic oxygen consumption in Atlantic cod Gadus morhua.

Area of Science:

• Marine biology
• Fish physiology
• Aquatic respiration

Background:

• Understanding fish physiological responses to hypoxia is crucial for predicting impacts of climate change on marine ecosystems.
• Atlantic cod (Gadus morhua) are commercially important fish facing increasing hypoxic events in their habitat.

Purpose of the Study:

• To quantify the oxygen deficit and subsequent excess post-hypoxic oxygen consumption in Atlantic cod exposed to severe hypoxia.
• To assess the energetic cost of anaerobic metabolism during hypoxic recovery in this species.

Main Methods:

• Atlantic cod were exposed to progressively decreasing oxygen levels until reaching their critical oxygen level.
• Post-hypoxia, oxygen consumption was measured under normoxic conditions to determine excess post-hypoxic oxygen consumption (CEPHO).
• The ratio of CEPHO to oxygen deficit (D O2) was calculated to assess the energetic cost.

Main Results:

• Atlantic cod exhibited a significant oxygen deficit (D O2) when oxygen levels dropped below their critical threshold (approximately 73% of pcrit).
• Upon return to normoxia, fish displayed substantial excess post-hypoxic oxygen consumption (CEPHO), indicating an oxygen debt.
• The mean CEPHO:D O2 ratio was 6.9 ± 1.5, signifying a high energetic cost associated with anaerobic metabolism during recovery.

Conclusions:

• Atlantic cod incur a considerable oxygen debt when subjected to severe hypoxia.
• The high energetic cost of anaerobic metabolism suggests that recovery from hypoxic events is metabolically demanding for this species.
• These findings highlight the potential vulnerability of Atlantic cod populations to oxygen-depleted environments, particularly under future climate scenarios.