ONTOGENY OF IGM AND IGM-BEARING CELLS IN RAINBOW-TROUT

We have studied the ontogenic development of immunoglobulin M (IgM) an d of IgM-bearing cells in the rainbow trout, Oncorhynchus mykiss. Lymp hocytes showing cytoplasmic IgM were first observed in embryos at 12 d ays before hatch (14-degrees-C). At this stage, no cells positive for surface IgM were present. Lymphocytes bearing surface IgM were observe d at 8 days before hatch (14-degrees-C). Unfertilized trout eggs conta ined detectable amounts of IgM (11.2 +/- 2.6 mug/g of egg weight), ind icating that transfer of IgM from mother to embryo can occur in salmon ids. The levels of IgM from whole fish increase slowly after the appea rance of intraembryonic cells that express surface IgM. The amount of IgM/g of tissue peaks around hatch, but this parameter shows lower val ues up to 2 months after hatch.