In this study, we examined the mRNA level in the pituitary of goldfish and observed a significant increase by PrRP treatment and a decrease by the antibody (Fig.1) although the possible effects of the antibody on other peptides cannot be excluded. In addition to stimulations of PRL by exogenous PrRP observed repeatedly in mammals and teleosts, we first showed that endogenous PrRP is essential to maintain the normal PRL expression.