CHANGES IN AN IMMUNOGLOBULIN-M (IGM)-LIKE PROTEIN DURING LARVAL STAGES IN TILAPIA, OREOCHROMIS-MOSSAMBICUS

Changes in an immunoglobulin (IgM)-like protein (MLP) were measured using an enzyme-linked immunosorbent assay (ELISA) in larval tilapia, Oreochromis mossambicus, obtained from a non-immunized mother. MLP levels during pre-larval stages decreased gradually, as yolk was absorbed. At 12 days after hatching, all yolk had been utilized, and the onset of feeding and free swimming was observed. About this time, MLP dropped to its lowest levels. The MLP levels during post-larval stages increased rapidly. These findings suggest that the MLP detected in the pre-larval stages is derived from maternal fish, and that its anti-pathogenic role, if any, lasts until the onset of feeding. Moreover, it is likely that the MLP detected during the post-larval stages was IgM produced by larvae themselves. The transition from maternally-derived substances to autogenous humoral defence molecules is discussed in respect of non-specific defence processes in the serum.