Evaluation of phagocytic activity in a teleost fish, Dicentrarchus labrax

Following stimulation by bacterial ( Aeromonas salmonicida) and fungal ( Candida albicans) pathogenic agents, the phagocytic function of the macrophages of a marine fish, Dicentrarchus labrax, was demonstrated and analysed by two techniques: light microscopy allowed visualization and quantification of this non-specific immune activity, while the kinetics of reactive oxygen intermediate production were analysed by measurement of luminol-dependent chemiluminescence (CL). The CL of macrophages isolated from the pronephros provided an indication of the intensity of the ‘respiratory’ or ‘oxidative’ burst accompanying phagocytosis. The ratio of macrophage: pathogenic agents and the amplitude of the CL response varied with the type of pathogenic agents. Agents isolated from marine organisms activated the phagocytic cells of sea bass more than the same micro-organisms isolated from mammals, and those opsonised by fish serum increased the macrophage CL response.