Ontogenetic changes of circulating erythroid cells and haemoglobin components in Esox lucius

Using light microscopy the morphology, the mitotic index and levels of erythroid cell types were detected from 48 h pike Esox lucius embryos before hatching to adult specimens. At the same developmental stages, the haemoglobins and globin chains expressed were electrophoretically characterized. The erythroid cells of the primitive generation were the most abundant from 48 h before hatching until 15–20 days after hatching, then their number decreased and only rare cells remained in the 3 month‐old juvenile specimens. These cells divided and differentiated in the blood and were substituted by the definitive erythrocyte series. As in other vertebrates, the immature cells of the two generations differed in morphological properties and in the synthetized haemoglobin. The circulating erythroid cells of the definitive population cell lineage were, at all differentiation stages, smaller than those of the primitive generation. The definitive erythrocytes appeared in blood smears of 7 days post‐hatching larvae, they increased rapidly and at 20 days they represented the predominant red blood cell population in the circulation of young pike. Electrophoretic analysis of haemolysates obtained from different developmental stages indicated the presence of distinct embryonic, larval and adult haemoglobins. The embryonic haemoglobins differed from those of the older larva and juvenile specimens and were detectable within the first week of post‐hatching development when only primitive erythrocytes were present in the blood.