Degradation kinetics of immunoglobulin in the egg, alevin and fry of Atlantic salmon,Salmo salarL., and the localisation of immunoglobulin in the egg

The presence of immunoglobulin (Ig), or an antigenically cross-reacting molecule, in eggs, alevin and fry of Atlantic salmon was quantified using an enzyme-linked immunosorbent assay (ELISA). A positive correlation was found between the Ig level in plasma of a mature female salmon and the Ig content in her eggs. There was a gradual decline in the Ig level in the egg homogenates from the day of fertilisation and through incubation, and the decline continued during the alevin stage, until very low levels were present by onset of first feeding (day 130 after fertilisation). Thereafter, Ig levels in the fry homogenates increased rapidly, probably due to autologous synthesis. An immunohistochemical technique was used to demonstrate the localisation of Ig in unfertilised eggs. Reactivity for salmon Ig was most prominent at the inner margin of the egg membrane and reactivity was not detected in the egg yolk. The inner surface of the egg membrane showed a weak diffuse staining for Ig interspersed with intense foci of staining that were arranged in a pattern typical of pores. The egg membrane also showed reactivity for Ig in linear structures that presumably represented the pore canals.