THE TRANSPORT OF OXYGEN BY THE BLOOD OF FRESHWATER FISH

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Abstract
Oa dissociation curves were constructed for the whole blood of certain freshwater fish. The equilibrations were carried out at 15[degree]C. and at various pressures of CO2. Heparin was used as the anticoagulant. The integrity and respiration of the erythrocytes were not impaired by the addition of substances like citrates, oxylates or NaF. The fish studied were the bowfin (Amia calva); common sucker (Catostomus commersonii); carp (Cyprinus carpio); catfish (Ameiurus nebulosus). O2 capacities and red cell vol. were detd. The specific differences in the affinity of the Hb for O2 are revealed by the pO2 necessary for half saturation in the virtual absence of CO2: catfish, 1.4 mm. O2; carp, 5 mm.; bowfin, 4 mm.; common sucker, 12 mm. Specific differences were likewise observed in the sensitivities of the whole blood to CO2, a fact already noted for other spp. of fish by other workers. Blood with a low sensitivity towards CO2 has a high affinity for O2 (catfish) and blood with a high sensitivity towards CO2 has a low affinity for O2 (common sucker). Since blood characterized by high O2 affinity apparently lacked a large CO2 effect to offset the disadvantages imposed at deoxygenation, the blood functioned best in a high environmental temp. The greater sensitivity to CO2 of fish blood as compared with mammalian blood was regarded by Krogh and Leitch as an adaptation to lower temp. Evidence shows that certain freshwater fish with blood of higher CO2 sensitivity are found in the colder habitats.

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