SummaryThe influence of water‐borne iron (500 μg × 1‐1and 2 mg × 1‐1) on the liver ofPoecilia reticulatais studied by means of electron microscopy. The uptake and effect of iron is affected by a. the chemical speciation of the metal: Iron complexed with tri‐polyphosphates is more deleterious than inorganic Fe3+; b. the nutritional status of the fish: In food‐deprivedPoecilia reticulatairon is absorbed and enhances starvation‐induced liver damage. In fed animals, there is no uptake at all. Mild alterations of hepatocyte ultrastructure are attributed to an unspecific s