Vitellogenin (Vtg) is found in the serum of both female and male fish that have been exposed to environmental endocrine disrupters or estrogen hormones, and is used as a biomarker for such contamination. In our current study antibodies raised against the purified flatfish Vtg were tested for their reactivity on immunoblots to flatfish and carp Vtg, and also to a Vtg protein fragment produced in E. coli. Polyclonal antibodies raised against purified flatfish Vtg reacted well with Vtg in the serum of flatfish and carp induced with $17{eta}$-estradiol, but not with the Vtg protein fragment produced in E. coli.