Hematology of Anemia Experimentally Induced by Repeated Bleedings in Japanese Flounder with Comments on the Cause of Flounder Anemia Recently Prevailing in Japan

Abstract

To clarify the causative agent of the anemia that has been recently prevailing in wild and cultured Japanese flounder Paralichthys olivaceus, anemic flounder were generated by repeated bleedings and examined hematologically. When flounder were bled once a week at 0.5 or 1.0% (volume/body weight) for 12 weeks without feeding, severe anemia developed in the fish.The anemia showed significant reductions in the hemoglobin concentration, mean corpuscular cell volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration, and structural anomalies of erythrocytes occurred such as low hemoglobin accumulation in the cytoplasm and a deformed outline. The hematological characteristics of the anemia caused by the repeated bleedings was almost identical to the anemia observed in wild Japanese flounder, supporting the previous conclusion that the blood-feeding activity of the monogenean Neoheterobothrium hirame is the cause of the anemia. Even after the last bleeding, it required 8 weeks for the anemic fish to recover in a feeding condition. The long period needed for the recovery also supports the previous conclusion that the anemic wild fish without N. hirame can be recognized as fish in the recovering phase from the anemia.