Transfer of maternally-derived immunoglobulin (IgM) to larvae in tilapia,Oreochromis mossambicus

Changes in circulating immunoglobulin (IgM) during development of larval tilapia,Oreochromis mossambicus, were measured by enzyme-linked immunosorbent assay (ELISA). During the prelarval stages, low levels of IgM were detected in the larval blood, while relatively high IgM was observed in the larval homogenate. This difference suggests that most of the IgM is of maternal origin and remains in the yolk sac of the larva. During the post-larval stages, IgM levels increased in the larval blood, coinciding with changes in IgM in the larval homogenate. These results suggest that the immune system starts maturing during the post-larval stages. Immunisation of the maternal fish with bovine serum albumin (BSA) increased the antibody titre in the maternal sera and their 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 circulation. In the post-larvae, antibody levels to BSA in the larval circulation decreased to background, suggesting that the maternal antibody is metabolised gradually by the larvae during the prelarval stages and does not last through the post-larval stages.