Another common response to low oxygen is aquatic surface respiration. In this
behaviour, fish stay just below the surface, put their snout at the air-water interface,
and breathe in the film of water that is in direct contact with the air. This thin layer of
water is comparatively rich in oxygen. Once I have seen this behaviour done by wild
sticklebacks in a tide pool. It was a very warm summer night without wind. The
water in the pool did not hold its normal load of dissolved oxygen because it was
warm, the absence of wind prevented mixing, and aquatic plants could not
photosynthesise in the dark and therefore did not produce any oxygen.
In the lab, Don Kramer and Martha McClure studied 24 species of tropical fish
common to the pet trade, from tetras to barbs to cichlids. They found that all of these
fishes performed aquatic surface respiration when oxygen was deficient. Typically,