THE RESPIRATORY FUNCTION OF THE BLOOD OF MARINE FISHES

Abstract

1. The oxygen capacities of marine fish bloods are quite different for different species. The greatest difference is between the typically sluggish and active forms, the former having bloods of low, and the latter bloods of high oxygen capacity. There is a general correlation between oxygen capacity and corpuscle count, corpuscle volume, and iron content. 2. Studies on the oxygen dissociation curves of marine fish hemoglobin, and on the effect of carbon dioxide on the oxygen capacity have brought forth the suggestion that the effect of carbon dioxide on the hemoglobins of these fishes is not solely on their oxygen dissociation constants, but that there is an inactivation of certain of the prosthetic groups concerned in binding oxygen in the hemoglobin molecule, causing a marked decrease in oxygen-combining power of the bloods. The most marked evidence of inactivation occurs at definite ranges of carbon dioxide tension and pH for the different bloods. 3. The carbon dioxide-combining power of fish bloods appears to be correlated with hemoglobin concentration. Mackerel blood with high hemoglobin absorbs more carbon dioxide than toadfish blood, which has a low hemoglobin concentration. 4. Reduced fish blood will absorb slightly more carbon dioxide than oxygenated blood. For sea robin and toadfish bloods the range of carbon dioxide tension where this can be demonstrated is short, being between about 2 and 25 mm., while it is longer for mackerel blood, being about 2 to 95 mm. 5. There is a differential buffering ability shown by these bloods, mackerel blood being buffered the best and toadfish the poorest. 6. Comparative studies of vertebrate bloods strengthen the idea of specificity of hemoglobins. Those of the marine fishes are far more sensitive to carbon dioxide than those of the carp, turtle, and human. 7. Comparative studies on carbon dioxide transportation show that turtle and frog bloods have a relatively great, fishes a relatively small, and human blood a more or less intermediate carbon dioxide-combining power. The bloods also vary considerably in their buffering capacity, human blood having the greatest and toadfish blood the least. 8. The general results of this investigation point to an adjustment on the part of the blood of marine fishes to a sea-water environment, and the habits or characteristics of the fishes. At the same time the comparative studies indicate marked differences between the bloods of fishes and terrestrial vertebrates. These differences can perhaps be accounted for on the basis of the new morphological and physiological features that terrestrial vertebrates have acquired, along with change in environment, which have made necessary correlative changes in the respiratory function of the blood.