Phagocytic cells in blood from rainbow trout, Salmo gairdneri (Richardson), characterized by flow cytometry and electron microscopy

An in vitro assay for estimating the proportion of phagocytic cells among peripheral leucocytes from rainbow trout by flow cytometry (FCM) and fluorescence microscopy was evaluated. Data from FCM were compared with fluorescence microscopic observations and good correlation ( r = 0.87) was found. The influence of various culture conditions, such as serum type, duration of incubation and temperature, on the in vitro phagocytic assay was investigated. Cultures supplemented with brown trout serum and incubated for 18 h at 19° C were considered to give optimal conditions for phagocytosis. The proportion of phagocytic cells detected in the peripheral blood leucocyte preparation was 3.3 ± 1.5% with FCM and 5.5 ± 2.4% with fluorescence microscopy. The applicability of the method was demonstrated in a preliminary study with arsenic. In a concentration of 1 μg ml⁻¹, arsenic increased the proportion of actively phagocytic cells, but, at a high concentration, 100 μg ml⁻¹, it decreased the phagocytic activity. Electron microscopy was used for morphological classification of the peripheral leucocytes throughout the study.