IgM levels and specific antibody activity of the flounder (Platichthys flesusL.), following injection of microsporidian spores

An investigation of phagocytic functions (phagocytosis assay, chemilumi-nescence and serum opsonizing activity) was undertaken in three successive generations of rainbow trout resulting from a selection programme performed on the basis of parent susceptibility or resistance to experimental furunculosis infection. Several experiments aimed to test the opsonizing activity of individual sera for a non-virulent strain ofAeromonas salmonicidapresented to anterior kidney cells of independent donor fish. Another experiment compared the phagocytic properties of anterior kidney cells collected from individual trout of different families. Although differences among progenies were detected for opsonizing properties of the serum and for the basic phagocytic activity of the cells in the absence of opsonization, opsonizing properties and phagocytic activities were never statistically correlated with the resistance of the fish to furunculosis. We observed: (1) significant differences in opsonizing values between two series of sera collected at different times in the same generation, which could be due to a seasonal influence on the opsonizing activity of sera; (2) a negative correlation between opsonization and the bactericidal activity of serum in the phagocytosis assay, and (3) a very low correlation between the basic phagocytic activity against non-opsonized bacteria and the bactericidal activity of serum. Neither phagocytic cells nor opsonizing properties of serum seem likely to explain the resistance of fish to furunculosis in the subfamilies resulting from our selection programme.