Larvae of air-breathing fishes as countercurrent flow devices in hypoxic environments.
Larvae of the air-breathing teleost fish Monopterus are frequently exposed to periods of critical hypoxia, which they can survive because they have (i) dense capillary networks in the skin, (ii) a small blood-water barrier, (iii) an active pectoral fin mechanism that generates a posteriorly directed respiratory water current originating from the oxygen-rich surface layer, and (iv) a principal flow of blood that runs countercurrent to the water stream. Experimental data show that the larva as a whole is a functional analog of a fish gill lamella and that similar adaptive mechanisms are present in larvae of ancient fishes and some modern teleosts inhabiting permanently or periodically hypoxic waters.
D000818:Animals; D003377:Countercurrent Distribution; D005399:Fishes / Q000196:embryology / Q000502:physiology*; D000860:Hypoxia / Q000378:metabolism; D010101:Oxygen Consumption; D012119:Respiration