Stress-related changes in the hematological profile of the American eel (Anguilla rostrata)

The authors investigated the impact of environmentally realistic concentrations of cadmium (Cd) on the hematological responses of the eel to acute stress. After 8 weeks of exposure to 150 micrograms Cd/liter, there was a significant reduction in the total erythrocyte count, hemoglobin (Hb), and hematocrit (Hct). Total leukocyte counts, leukocrit, and large lymphocytes were significantly increased, while the proportion of small lymphocytes fell. After 8 weeks of Cd exposure, acute stress was induced by a 2-min exposure to CO2 bubbles. The untreated control fish responded strongly by erythrocyte swelling, which was evident from a marked increase in the Hct and mean cellular volume, and a decreased mean cellular hemoglobin concentration. Furthermore, there was a marked granulocytosis and a strong drop in the thrombocyte count. After Cd treatment, the erythrocyte changes were attenuated and shorter, granulocytes were increased, and there was no drop in the thrombocyte count. It appears that the Cd exposure decreased the erythrocyte response to adrenergic stress signals. It also decreased the stress-related granulocytosis, and it prevented the drop of the thrombocyte count.