TRANSFER OF MATERNALLY-DERIVED IMMUNOGLOBULIN (IGM) TO LARVAE IN TILAPIA, OREOCHROMIS-MOSSAMBICUS

Changes in circulating immunoglobulin (IgM) during development of larv al tilapia, Oreochromis mossambicus, were measured by enzyme-linked im munosorbent assay (ELISA). During the prelarval stages, low levels of IgM were detected in the larval blood, while relatively high IgM was o bserved in the larval homogenate. This difference suggests that most o f the IgM is of maternal origin and remains in the yolk sac of the lar va. During the post-larval stages, IgM levels increased in tile larval blood, coinciding with changes in IgM in the larval homogenate. These results suggest that the immune system starts maturing during the pos t-larval stages. Immunisation of the maternal fish with bovine serum a lbumin (BSA) increased the antibody titre in the maternal sera and the ir egg homogenates. Identical antibody titre was also detected in the blood of prelarvae. These results suggest that antibody raised in the maternal circulation is incorporated into vitellogenic oocytes in the ovary and transferred from the larval yolk sac into the larval circula tion. In the post-larvae, antibody levels to BSA in the larval circula tion decreased to background, suggesting that tl-le maternal antibody is metabolised gradually by the larvae during the prelarval stages and does not last through the post-larval stages. (C) 1997 Academic Press Limited.