Analysis of Channel Catfish Peripheral Blood Leucocytes by Bright-Field Microscopy and Flow Cytometry

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Abstract
Peripheral blood leucocytes of channel catfish Ictalurus punctatus were characterized by Wrightˈs stain, differential cytochemical stains, and immunofluorescence; lymphocytes, thrombocytes, neutrophils, and monocytes were identified. The morphologically similar neutrophils and monocytes were distinguished with a Sudan black B stain for neutrophils and an assay of nonspecific esterase activity for monocytes. Monocytes also phagocytized polystyrene beads. Leucocytes were physically separated by cytofluorography based upon their forward and 90° light‐scattering properties. One population of sorted cells contained almost exclusively lymphocytes, a second contained predominantly thrombocytes, and the third contained both neutrophils and monocytes. Multiparameter cytofluorography with mouse monoclonal antibodies to channel catfish immunoglobulin revealed that a vast majority of leucocytes exhibiting surface immunofluorescence were lymphocytes, though only about 40% of the lymphocytes contained demonstrable surface immunoglobulin. These techniques were used to compare leucocytes of channel catfish acclimated to laboratory temperatures of 17, 22, or 27°C and fish obtained from production ponds during summer and winter. Although no differences were seen among these groups, preliminary experiments indicated that certain hematological variables changed significantly in stressed or infected fish. Received April 30, 1984 Accepted November 12, 1984