Hematological and cytochemical characteristics of peripheral blood cells in the argus snakehead ( Ophiocephalus argus Cantor)

Background The argus snakehead ( Ophiocephalus argus Cantor) is a highly nutritious, freshwater, cultured bony fish with a high economic value. The health of the fish is closely related to its blood cells, which are critical for oxygen transport, natural defense, and immunity. We investigated the morphometry, microstructure, and cytochemical characteristics of the peripheral blood cells of O. argus . Our results may provide the basic reference values needed to monitor the health of this fish for large-scale cultivation. Methods The number of blood cells in O. argus were counted on a hemocytometer and their size was measured using a micrometer under light microscope. The morphology and classification of the blood cells were studied using Wright’s staining and the cytochemical characteristics were studied using seven chemical stains including peroxidase (POX), Sudan black B (SBB), periodic acid-Schiff (PAS), acid phosphatase (ACP), alkaline phosphatase (ALP), chloroacetic acid AS-D naphthol esterase (AS-D), and α -naphthol acetate esterase ( α -NAE). Results The peripheral blood cells in O. argus can be classified as erythrocytes, leukocytes, and thrombocytes; of which, females had 2.9597 million/mm 3 , 88,400/mm 3 , and 43,600/mm 3 , respectively, and males had 3.0105 million/mm 3 , 105,500/mm 3 , and 34,000/mm 3 , respectively. Leukocytes consisted of neutrophils, monocytes, large lymphocytes, and small lymphocytes. Eosinophils and basophils were not found. Monocytes were the most numerous leukocytes identified, followed by neutrophils and small lymphocytes, while large lymphocytes were the least frequently identified. Cytochemical staining showed that erythrocytes were only positive for PAS staining. Neutrophils were strongly positive for POX, SBB, and ACP, and positive for all the other cytochemical stains. Monocytes were positive for PAS and α -NAE and were weakly positive for ACP and AS-D staining. Large lymphocytes were positive for PAS and were weakly positive for ALP, AS-D, and α -NAE staining. Small lymphocytes were positive for PAS and weakly positive for AS-D and α -NAE staining. Thrombocytes were positive for PAS and were weakly positive for ACP and AS-D, but negative for the remaining cytochemical stains. The morphology of peripheral blood cells in O. argus was generally similar to that of other fish species, while the cytochemical staining patterns showed clear species specificity.