Larvae of air-breathing fishes as countercurrent flow devices in hypoxic environments

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Science  13 Mar 1981:
Vol. 211, Issue 4487, pp. 1177-1179
DOI: 10.1126/science.7466391


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.