Morphogenesis of blood cell lineages in channel catfish

The morphogenesis of blood cell lineages in channel catfish Ictalurus punctatus , from head and trunk kidney and spleen imprints as well as from blood smears of bled and control fish, showed that early maturation stages resembled those in higher vertebrates. The erythroid lineage consisted of the proerythroblast, erythroblasts (basophilic, polychromatic, orthochromic), young erythrocyte and erythrocyte. The rare bilobed erythrocyte seemed to be a cell in apoptosis while old erythrocytes and erythroplastids represented remnants of this process. Maturation stages of neutrophils and basophils encompassed the granuloblast, young progranulocyte, progranulocyte and metagranulocyte. The basophilic lineage was regularly present in kidneys, rare in spleen and absent from blood. It contained large Sudan Black and PAS-negative, water soluble granules and small PAS-positive ones. Lymphocytes with azurophilic granulation occured regularly in kidneys and spleen. Monoblasts and promonocytes in kidneys preceded monocytes. A phagocytic lineage devouring apoptotic blood cell remnants was present in kidneys and spleen. Its youngest identified stage (promacrophage) resembled more a granuloid cell without granules than a monocytoid one. The larger, young macrophages contained a few to several ingestions and the very large mature macrophages were loaded with them. The latter two stages corresponded to cells in melano-macrophage centres (macrophage aggregates). Precursor stages of the thrombocyte were not identified.