Sickling of anoxic red blood cells in fish

The occurrence of the mutant hemoglobin Hb S in human red blood cells results in sickle cell anemia. This disease, including its genetic and molecular bases, has been extensively investigated and is well understood (1,2). The presence of deoxy-induced sickling of animal erythrocytes is largely unknown, however. We examined red blood cells (RBCs) from several fish species in vitro under aerated and anoxic conditions. Our polarized light microscopic techniques were aimed at establishing correlations between erythrocyte morphology, state of oxygenation, spectral absorbance, linear dichroism, and linear birefringence. We found no fish with intracellular HbO2 polymerization; but there were intraerythrocytic aggregations of deoxy Hb with a high degree of either molecular order or disorder. The ordered aggregates in the RBCs of Atlantic cod, haddock, and toadfish were remarkably similar in dichroic ratio magnitudes and birefrigence to those in human RBCs that contain HbS. Therefore, fish hemoglobins appear to be good models of sickling disorders and polymerization-related phenomena. The consequences of sickling on animal health and fish aquaculture remain to be studied.