Maturation of circulating red blood cells in young baltic salmon (Salmo salar L.).

The maturation of circulating red blood cells (RBC) in salmon (Salmo salar L.) has been studied. A developmental RBC series of 6 classes based on morphological criteria was proposed. After a single dose of iron (55Fe) given to 5-6 months old salmon the incorporation of radioactivity in maturing RBC was followed by autoradiography on blood smears. The relative distribution of labelled RBC between the 6 classes in specimens taken 15, 20, 41, and 52 days after the injection of iron showed that the RBC matured along the proposed series. The projected area of the RBC increased by 100% during the maturation. This RBC growth was caused by an elongation of the RBC. Thus the ratio between short and long axes of the RBC decreased with maturation and can be used as a measure of the degree of maturation. The uptake of radioactive iron measured as grain count per RBC or per projected area of the RBC increased during the maturation in classes II-IV. Radioactive iron was not incorporated by mature RBC. The maturation time from class I to class VI was shorter than 41 days. RBC iron bound to non-haemoglobin proteins as a possible restriction in estimations of the haemoglobin concentrations of developing RBC is discussed.