THE RELATIVE NUMBERS OF IMMATURE ERYTHROCYTES IN THE CIRCULATING BLOOD OF SEVERAL SPECIES OF MARINE FISHES

¹ From the Zoölogical Laboratories, Harvard University, and the Marine Biological Laboratory, Woods Hole, Massachusetts

The results of a study of the blood of the general circulation of twenty species of marine fishes are given. The number of immature erythrocytes present varies widely.

The differential erythrocyte counts were based largely on supravital preparations stained with brilliant cresyl blue. This material was supplemented by dry-fixed smears stained by Wright's method. The reticulation patterns produced by brilliant cresyl blue are discrete structures and more accurate counts can be made on these preparations than on stained smears where the varying degrees of basophilia and polychromasia are used as criteria of immaturity.

The twenty species of fish examined fall naturally into four groups. In Group I, including the mackerel, menhaden, alewife, summer herring, bluefish and common eel, the proportion of immature erythrocytes is high, approximately 20 per cent. In the second group, including the variegated minnow, sea robin, scup, and butterfish the percentage of immature cells is lower, varying between 3 and 6 per cent. In the third group, including toadfish, tautog, cunner, sea bass, pipefish, sand dab, weakfish and sharksucker, practically all the erythrocytes are mature. The fourth group, comprised of elasmobranchs, was treated separately since in these forms erythrocytes are continuously differentiated in the blood stream from primitive cells and may also proliferate mitotically in this location. The number of immature red cells in these fish is also great.

The varying blood pictures appear to represent the result of specific adaptations of fishes to such interrelated factors as their type of external respiratory mechanism, the efficiency of their oxygen-transporting system, their oxygen requirements and the oxygen tensions of their environment. In Group I the general blood picture is suggestive of the high-altitude effect observed in mammals.

Many of the fishes with high counts of immature erythrocytes quickly exhibit signs of asphyxiation when removed from their natural habitat and kept in tanks. Hall has noted that during asphyxiation the spleen of fishes decreases in volume. This may be correlated with the entrance of immature erythrocytes into the general circulation. Accordingly, it is possible that the figures presented in this paper are not exactly representative of the condition of the blood when such fish are undisturbed in their natural environment.