Genetic differences in natural antibody levels in common carp (Cyprinus carpio L.)

In mammals, natural antibodies (Nabs) are mostly of the IgM isotype and can bind to a particular antigen or pathogen even if the host has never been exposed. Despite their early detection and abundance, the exact role and genetic control of Nabs remain unclear. We have used an indirect ELISA with three different antigens (keyhole limpet haemocyanin, chicken ovalbumin and bovine serum albumin) to demonstrate the ubiquitous presence of Nabs in common carp. Serum levels of Nabs increased with age, i.e. 10-month-old fish showed higher levels than 4-month-old fish. Also, fish grown in earth ponds showed higher levels of Nabs than fish grown in a clean environment of UV-treated water. Furthermore, we show that Nabs are present in different levels in the serum of carp lines with a different genetic background, suggestive of a genetic control. These genetic differences were independent of antigen, age and environment. Genetic differences in levels of Nabs could not unequivocally be related to differences in survival under farmed conditions. The possibilities for using levels of Nabs as marker criterion for selection for genetic disease resistance are discussed.