I’d just call that respiration. Every definition of breathing I can find is particular to lungs.
Edit: Actually, that’s not true—I found a dictionary that lists a broader metaphorical usage that encompasses all respiration (including plants and fish).
Is it accurate to say fish don’t breathe? I’ve seen fish gulp at water to (presumably) push over their gills. Seems kind of like breathing to me.
I’d just call that respiration. Every definition of breathing I can find is particular to lungs.
Edit: Actually, that’s not true—I found a dictionary that lists a broader metaphorical usage that encompasses all respiration (including plants and fish).