The effect of iron on hematocrit levels in tropical fish

Although the amount of iron present in the body is small (in humans about 45 milligrams/kilogram of body weight), it is an essential constituent of hemoglobin and of the cytochrome respiratory enzyme system, and thus an element of fundamental importance. The absorption of iron is different from that of other elements; most minerals are absorbed freely and the excess excreted. Once iron is absorbed, however, most of it is retained within the body. Only minute amounts are excreted, and that present in the body is almost completely reutilized after metabolic breakdown of the iron containing compounds, e.g., hemoglobin. Thus if the excess iron is not excreted, there appears to be a mechanism for absorption control. (Granick, 1946)