Temperature effects on the blood oxygen affinity in sharks

Area of Science:

• Marine Biology
• Comparative Physiology
• Biochemistry

Background:

• Regional endothermy, the ability to maintain elevated tissue temperatures, is found in few fish groups, including some sharks and teleosts.
• Hemoglobin's (Hb) oxygen affinity typically decreases with rising temperatures, impacting oxygen delivery to tissues.
• Adaptations in Hb-oxygen affinity are crucial for endothermic species, but remain largely unstudied in sharks.

Purpose of the Study:

• To investigate the effects of temperature on blood oxygen affinity in different shark species.
• To compare these effects between regionally endothermic and ectothermic sharks.
• To understand the physiological adaptations supporting regional endothermy in sharks.

Main Methods:

• Measured blood oxygen-binding affinity across a range of temperatures (10–25 °C).
• Studied two pelagic sharks: the regionally endothermic shortfin mako shark and the ectothermic blue shark.
• Included two coastal ectothermic species: the leopard shark and brown smooth-hound shark.

Main Results:

• Shortfin mako shark blood showed less temperature-dependent oxygen affinity compared to ectothermic sharks.
• This adaptation in mako sharks may prevent premature oxygen release in warm swimming muscles.
• Blue shark blood oxygen affinity was similar to coastal ectothermic species, differing from mako sharks despite occupying a similar niche.

Conclusions:

• Shark blood oxygen affinity exhibits species-specific responses to temperature.
• Regional endothermy in sharks, like tunas, may involve Hb-O2 affinity that is less sensitive to temperature.
• Leopard shark blood showed a unique reverse temperature effect, possibly linked to its estuarine environment.