Rapid renewal of red blood cells in the common carp following prolonged exposure to air

Abstract

Air exposure causes extreme stress in fish. Most fish die within minutes when exposed to air; however, the common carp Cyprinus carpio can survive in air for several hours. To understand the hematological response following prolonged air exposure and its association with zinc, common carp were exposed to air for 4 h and allowed to recover in an aquarium for 140 h at 25 °C. Hematological analysis and microscopic examination of the blood cells revealed that during the recovery period, the total RBC count remained relatively constant, but the RBC composition changed greatly. After 20 h of recovery, 35 % of the mature RBCs had degraded and were replaced by immature RBCs. Among the RBCs that were renewed, 15 % were likely derived from the release of stored RBCs from the spleen immediately after air exposure, and the other 20 % appeared to be generated via erythropoiesis. An increase in the rate of erythropoiesis in the common carp was triggered and facilitated by zinc in the head kidney. The renewed RBCs had significantly higher osmotic resistance than RBCs obtained from fish at rest. These results suggest that the replacement of one-third of mature RBCs with immature RBCs can increase fish tolerance to stress.