Composition, structure and cytochemical characteristics of peripheral blood cells in Paralichthys olivaceus

Abstract The microstructures, classification, counting and size of peripheral blood cells in Paralichthys olivaceus were observed and measured by Wright-Giemsa staining, and the cytochemical characteristics of peripheral blood cells were investigated by different cytochemical staining methods. Besides, the transmission electron microscope was used to observe the ultrastructures of different cells. The results showed that erythrocytes, thrombocytes and leukocytes constituted the peripheral blood cells in Paralichthys olivaceus, and leukocytes were made of monocytes, neutrophils and thrombocytes. More heterochromatins were found in erythrocytes, thrombocytes and neutrophils, however, monocytes had more organelles with fewer heterochromatins. As for neutrophils, endoplasmic reticulums and phagocytic vesicles were abundant. The number of erythrocytes was the highest, and the size of lymphocytes and thrombocytes was the smallest; while neutrophils were the fewest in number but the largest in size. Lymphocytes were the most abundant in leukocytes, followed by monocytes and neutrophils. The cytochemical staining results showed that all leukocytes were positive for SBB. Most of the lymphocytes were positive for PAS, and monocytes were positive for PAS, ACP and POX. As for neutrophils, ACP and POX were positive. Both monocytes and neutrophils showed positive for SBB, ACP and POX, indicating that the two kinds of cells play a vital role in phagocytosis and bactericidal action. Only lymphocytes were positive for ALP, indicating that they were important in inflammation and immune response. Paralichthys olivaceus shared the characteristics similarities in peripheral blood cells with other fishes. However, obvious differences also existed, which reflected the species speciality. These results could enrich the haematological database of bony fish and provide scientific references for researching the cell function and evaluating the health status in Paralichthys olivaceus based on haematological parameters.