THE BLOOD OF THE ATLANTIC SALMON DURING MIGRATION

¹ From the Edward Martin Biological Laboratory, Swarthmore College, Swarthmore, Pennsylvania

The blood of Atlantic salmon caught in the brackish water of Gaspé Bay has been compared with the blood of salmon caught in the fresh water of the rivers draining into the Bay. In brackish and fresh water the average properties of the blood are respectively: oxygen capacity, 12.3 and 8.8 volumes per cent; cell volume, 39.4 and 24.8 per cent; oxygen tension for half saturation at T CO₂ = 1 mm., 23 and 19 mm.; freezing point of the serum, —0.79 and —0.64. The oxygen combination at P O₂ = 150 mm. in the presence of large tensions of CO₂ is reduced to about 60 per cent of saturation. Hemolysis does not much reduce the CO₂ effect. The cells swell greatly as the CO₂ tension is increased. There appears to be a dilution of the blood as the fish goes from salt to fresh water. This is seen in the decrease in cell volume, oxygen capacity, and freezing point depression of the blood. It seems also that in fresh water the affinity of the hemoglobin for oxygen is greater than in salt water. The changes observed in the blood may be related to the change in salinity of the environment. In the warm water of rivers in summer small changes in temperature and oxygen saturation may be critical in determining whether or not the blood can be saturated with oxygen.