Blood oxygen capacities of eels acclimated to fresh-, brackish- and salt-water environments

Abstract

1. Groups of American eels, Anguilla rostrata, were acclimated to three environmental salinities and their blood oxygen capacities determined. 2. The brackish-water group exhibited the highest mean oxygen capacity and weight-specific oxygen capacity. 3. Highly significant differences ( P < 0·001) were demonstrated between the oxygen capacities of the freshwater and marine groups and between the brackish water and marine groups. A significant difference was not observed between the freshwater and brackish-water eels. 4. Weight-specific blood oxygen capacities for the three groups exhibited an inverse relationship with body weight. 5. The American eel, under different salinity regimes, shows a relationship between oxygen capacity and hematocrit, which appears to be altered by ambient salinity. 6. The lower oxygen capacities and hematocrits observed in the salt water-acclimated eels suggests that the yellow eel is programmed for a freshwater and/or brackish-water existence and that acclimation to higher salinities disrupts its normal blood—oxygen relationships.