Enhanced oxygen unloading in two marine percomorph teleosts

Area of Science:

• Physiology
• Comparative Biology
• Biochemistry

Background:

• Teleost fish, comprising nearly half of vertebrate species, exhibit remarkable diversity and success.
• Their success may be linked to a unique oxygen (O2) transport system involving pH-sensitive hemoglobin and red blood cell (RBC) mechanisms.
• This system includes a beta-adrenergic Na+/H+ exchanger (β-NHE) in RBCs and plasma-accessible carbonic anhydrase, facilitating O2 unloading during stress.

Purpose of the Study:

• To investigate the presence and function of the RBC β-NHE in warm-water marine teleosts, specifically cobia (Rachycentron canadum) and mahi-mahi (Coryphaena hippurus).
• To characterize the hemoglobin-O2 transport system in cobia, including O2 equilibrium curves (OECs).
• To assess the potential for enhanced O2 unloading mediated by RBC β-NHE short-circuiting in these species.

Main Methods:

• Assessed RBC swelling in response to beta-adrenergic stimulation in cobia and mahi-mahi.
• Generated O2 equilibrium curves (OECs) for cobia blood.
• Determined P50, Hill, and Bohr coefficients for cobia hemoglobin.
• Modeled potential O2 unloading based on experimental data.

Main Results:

• Demonstrated significant RBC swelling in both cobia and mahi-mahi following beta-adrenergic stimulation, indicating active RBC β-NHE presence and function.
• Characterized cobia's Hb-O2 transport, yielding P50, Hill, and Bohr coefficients.
• Modeled O2 unloading, revealing a potential increase of up to 61% associated with RBC β-NHE short-circuiting.

Conclusions:

• The RBC β-NHE system is present and functional in diverse, active marine teleosts like cobia and mahi-mahi, similar to salmonids.
• The Hb-O2 transport system in cobia shows functional similarities to salmonids, despite phylogenetic and life history differences.
• This suggests a conserved physiological trait for enhanced O2 unloading across a wide range of teleost fish.