Effects of chronic hypoxia on the cardiorespiratory physiology of Atlantic cod (Gadus morhua)

• Main Author: Petersen, Lene Hebsgaard
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2010
• Subjects: atlantic cod; Gadus morhua
• Online Access: https://research.library.mun.ca/9146/; https://research.library.mun.ca/9146/1/Petersen_Lene.pdf

Currently, little information exists on how chronic hypoxia influences fish physiology. Thus, a comprehensive examination of how this ecologically-relevant environmental challenge affects the cardiorespiratory physiology, exercise performance and hypoxia tolerance of Atlantic cod (Gadus morhud) was performed. -- Exposure to acute hypoxia (PwO₂ 8-9 kPa) lowered the Ucrit of normoxic-acclimated cod by approx. 30%, and this was associated with large decreases in max. oxygen consumption (MO₂), metabolic scope (≥ 50%), and maximum heart rate (ƒH) and cardiac output (Q) (by 16 and 22%). Hypoxic acclimation (6-12 weeks at 10 °C; PwO₂ 8-9 kPa) elevated normoxic MO₂ (standard by 27 %; routine by 44%) compared with normoxic controls, but did not influence Ucrit, max. MO₂ or metabolic scope under either normoxia or hypoxia. Further, although, resting and maximum values for Q were significantly diminished in hypoxic-acclimated cod due to lower values for stroke volume (Sᵥ), increased ƒH partially compensated for the latter, and hypoxic-acclimated cod were able to consume more oxygen for a given cardiac output. -- This lower in vivo cardiac pumping capacity proved not to be a regulated decrease as hypoxic acclimation reduced in situ values for maximum Sᵥ, the scope for Sᵥ, and consequently maximum cardiac output (Qmax) (by 19%). However, hypoxic-acclimated fish were able to sustain Q better under hypoxia, and the recovery of Qmax (compared to initial Qmax) was significantly improved (94 vs. 83%) as compared with normoxic controls. -- Although several physiological adjustments had taken place during the 6-12 weeks of hypoxic acclimation [increased ƒH; elevated hematocrit (Hct) by 11 % and [Hb] by 14 %; enhanced tissue oxygen extraction efficiency by ~ 15%; and a more robust stress response (2-8 fold higher levels of plasma catecholamines at PwO₂'s of 5.3 and 2.7 kPa)], these adjustments were only successful in improving the cod's critical oxygen tension (Pcrit of normoxic and hypoxic-acclimated cod 8.1 ± 0.5 vs. 6.6 ± 0.6 ...