The Antarctic Icefishes Are the Only Known Vertebrates to Lack

The Antarctic icefishes are the only known vertebrates to lack hemoglobin. What would be LEAST likely to alter gas transport from the environment to an icefish's cells?

A) higher oceanic temperatures from global warming
B) higher concentrations of carbon monoxide in the water from pollution
C) higher concentrations of carbon dioxide in the water from pollution
D) an injury that reduces the surface area of gills