Hunt von Herbing, I.*; Cashon, B.: Sickling in fish red blood cells

The occurrence of the mutant hemoglobin Hb S in human red blood cells results in sickle cell anemia. In other animals,oxygen-linked sickling of red blood cells is largely unknown.In Atlantic cod red blood cells under oxygenated conditions cell morphology appears normal,but under low-oxygen conditions hemoglobin crystallizes resulting in sickled cells. To determine the oxygen linkage of this sickling phenomenon we inserted whole red blood cells of a freshly killed juvenile cod into a 1 mm thick glass cuvette and monitored changes in the morphology of the cells and formation of crystals using a compound microscope.Images were relayed through a high-resolution color video camera to a computer and captured using the OPTIMAS image analysis system. Simultaneously with the change of cell morphology we were able to monitor the spectral shift from oxy to de-oxy hemoglobin. We found that although 99% of the red blood cells contained hemoglobin crystals and were sickled, the shape of the red blood cells were not drastically altered. As a result, although oxygen transport may be modulated by the formation of crystals, transport within the vascular system may not be impeded under conditions of hypoxia. This differs from human sickle cells in which red cell morphology is radically distorted leading to occlusions within the vascular system which cause immense pain to the patient. Exposure to carbon monoxide reversed the sickling morphology. Sickling therefore appears to be ligand linked which is analogous to human sickle cell hemoglobin. Of the 12 other fish species tested, sickling occurred in 6 and appeared to be independent of life history stage and stock origin. However, sickling may be temperature dependent and be an adaptation to specific thermal regimes. Benefits of the sickling trait for survival and the reasons for its evolution in fishes is still unclear and is currently under investigation.