Adverse environmental conditions (contamination of water with nitrite, pesticides, or other pollutants), nutritional deficiencies, bacterial and viral infections, and parasitic invasions may induce anemia in fish, in both natural and aquaculture conditions. Changes in hematological values and cellular composition of peripheral blood and head kidney hematopoietic tissue of bled common carp (Cyprinus carpio L.) were evaluated over a 4 week period post-bleeding (30% blood loss). The results showed that fish very quickly compensated for anemia. Erythrocyte count (RBC), hemoglobin concentration (Hb), and hematocrit (Ht) gradually increased to values significantly higher than they were before bleeding; this was accompanied by an increase in erythroblast frequency in blood and in the head kidney. In addition, WBC count increased, which was probably related to lymphocyte release from the spleen or other lymphoid sites; the percentage of blood lymphocytes and lymphoid lineage in the head kidney remained unchanged. Neutrophil frequency in the blood was also unchanged; however rejuvenation of their population occurred, accompanied by a decrease in total neutrophil abundance in the head kidney. The percentage of circulating monocytes, basophils, and eosinophils decreased, which indicates that their recovery was slow. The obtained results revealed very high hematopoietic (particularly erythropoietic) capacity in the carp head kidney. This was indicated by a significant increase in the frequency of early blast cells (precursors of various cell lineages) and RBC precursor cells at various stages of development. This indicates that carp are able to recover from anemia caused by various adverse environmental and/or nutritional factors.

Adverse environmental conditions (contamination of water with nitrite, pesticides, or other pollutants), nutritional deficiencies, bacterial and viral infections, and parasitic invasions may induce anemia in fish, in both natural and aquaculture conditions. Changes in hematological values and cellular composition of peripheral blood and head kidney hematopoietic tissue of bled common carp (Cyprinus carpio L.) were evaluated over a 4 week period post-bleeding (30% blood loss). The results showed that fish very quickly compensated for anemia. Erythrocyte count (RBC), hemoglobin concentration (Hb), and hematocrit (Ht) gradually increased to values significantly higher than they were before bleeding; this was accompanied by an increase in erythroblast frequency in blood and in the head kidney. In addition, WBC count increased, which was probably related to lymphocyte release from the spleen or other lymphoid sites; the percentage of blood lymphocytes and lymphoid lineage in the head kidney remained unchanged. Neutrophil frequency in the blood was also unchanged; however rejuvenation of their population occurred, accompanied by a decrease in total neutrophil abundance in the head kidney. The percentage of circulating monocytes, basophils, and eosinophils decreased, which indicates that their recovery was slow. The obtained results revealed very high hematopoietic (particularly erythropoietic) capacity in the carp head kidney. This was indicated by a significant increase in the frequency of early blast cells (precursors of various cell lineages) and RBC precursor cells at various stages of development. This indicates that carp are able to recover from anemia caused by various adverse environmental and/or nutritional factors.