Search for a command to run...
Fish erythrocytes are ellipsoidal nucleated cells of different size (102–800 fl) and life span (13–500 days). Erythrocyte count depends on fish activity, water temperature and dissolved oxygen concentration as well as on other environmental factors and shows considerable seasonal variability. It is also dependent on age, sex, nutritional, and reproductive status, and may differ among various populations of the same species. It usually ranges from 0.5–1.5 × 106/mm3 in less active species to 3.0–4.2 × 106/mm3 in more active ones. Antarctic icefishes adapted to cold and well-oxygenated water lack erythrocytes. The head kidney is the main erythropoietic site in teleost fishes, and the process of erythropoiesis is similar to that in other vertebrates and involves the same precursors. Fishes show a weak barrier between hematopoietic tissue and circulating blood in which numerous immature cells are present, often comprising over 10% of all erythrocytes. As in other vertebrates, fish erythrocytes contain tetrameric hemoglobins of different oxygen affinity – lower in species living in well-oxygenated water than in those that experience hypoxia. Often several hemoglobin isoforms of different oxygen affinity are present in blood, which is considered an adaptation to variable oxygen concentration in water. Fish erythrocytes are sensitive to environmental pollution, and their morphological evaluation may be used as a bioindicator of toxicity.