Evidence for size-dependent cardiac oxygen supply in a fish

Area of Science:

• Physiological ecology
• Aquatic toxicology
• Fish biology

Background:

• Environmental resilience in fish is linked to gill oxygen uptake and cardiac oxygen supply.
• Size-dependent physiological limitations can impact fish survival under changing environmental conditions.

Purpose of the Study:

• To investigate the allometry of arterial (PaO2) and venous (PvO2) oxygen partial pressures in rainbow trout across a wide body mass range.
• To assess the effects of acute warming, hyperoxia, and exhaustive exercise on oxygen transport in relation to fish size.

Main Methods:

• Measured PaO2 and PvO2 in rainbow trout (282-3834 g) under various thermal and oxygen conditions.
• Applied acute warming (18-25°C) and hyperoxia (150% air saturation).
• Included protocols for exhaustive exercise and observed fish equilibrium.

Main Results:

• Arterial oxygen partial pressure (PaO2) scaling was not negatively affected by warming alone.
• Following exhaustive exercise, PaO2 significantly declined with body mass (b=-0.21) at 25°C.
• Venous oxygen partial pressure (PvO2) showed significant negative scaling with body mass (b=-0.34 to -0.37) at both temperatures, indicating reduced cardiac oxygen availability in larger fish.
• Hyperoxia benefited larger fish by mitigating the mass effect on PvO2.
• Loss of equilibrium occurred post-exercise irrespective of oxygen treatment.

Conclusions:

• Venous oxygenation scaling with size presents a novel constraint on oxygen transport in larger fish.
• Larger fish exhibit greater physiological vulnerability to combined thermal and physical stress.
• Conservation planning under climate change must consider size-dependent physiological vulnerabilities in fish populations.