The effect of cadmium on the hematology and on the activity of delta-aminolevulinic acid dehydratase (ALA-D) in blood and hematopoietic tissues of the flounder, Pleuronectes flesus L.

Flounders (Pleuronectes flesus) were exposed to sublethal levels of cadmium (5, 50, and 500 micrograms of Cd2+/liter) for periods of 4 and 9 weeks, and the hematological response as well as the effect on the activity of delta-aminolevulinic acid dehydratase (ALA-D) in blood and blood-forming tissues were investigated. Significant reductions of hematocrit, hemoglobin, and red blood cell count were found in the cadmium-exposed fish. This anemic response was apparent even in flounders exposed to the lowest cadmium concentration, approximately corresponding to 1/4000 of the 96-hr LC50 value. The anemia was accompanied by a significant increase of the ALA-D activity in renal tissues. This indicates a compensatory stimulation of the introductory steps of the hemoglobin biosynthesis. However, the formation of hemoglobin does not seem to be accomplished, which might be due to a disturbed iron metabolism. The cadmium exposure also resulted in a significant increase of the number of lymphocytes, indicating an action on the immunological defense of the fish.