Lack of antigenicity of human chorionic gonadotropin in silver carp (Hypophthalmichthys molitrix) and goldfish (Carassius auratus)

It has been suggested that the repeated use of human chorionic gonadotropin (hCG) to induce ovulation in fish results in the production of antibodies to hCG. These, in turn, may make the fish insensitive to hCG. For the present studies, we determined the antigenicity of hCG using serum samples collected from silver carp and goldfish that had been treated with hCG. The detection of antibodies to hCG was based on the capacity of the diluted serum to bind picogram quantities of 125I-labelled hCG. No antibodies to hCG were detected in naive silver carp or silver carp broodstock which had received multiple injections of hCG over several years in order to induce ovulation. Furthermore, no antibodies to hCG were detected in goldfish that had received multiple injections of hCG, either given alone or in combination with Freund's complete adjuvant. It appears that hCG may be less antigenic in fish than is commonly suggested, and that factors other than hCG antibodies contribute to ovarian refractoriness in broodstock induced to ovulate repeatedly with hCG.