Insulin-like growth factor (IGF) plays a key role in the complex system that regulates bony fish growth, differentiation, and reproductionIn the current study, recombinant tongue sole IGF-1 and IGF-2 were obtained using the Pichia pastoris expression system and their comparative bioactivities were investigated.Tricine-SDS-PAGE and western blot anal. showed that the recombinant tongue sole IGFs were secreted into the culture medium and had a mol. weight of 8.7 kDa.The optimal incubation time and pH for recombinant expression of IGFs were 36 h and 5.0 resp.Functional anal. demonstrated that both recombinant tongue sole IGF-1 and IGF-2 significantly promoted cell proliferation of MFC-7 in vitro.In addition, the recombinant tongue sole IGF-1 and IGF-2 proteins could suppress hepatic mRNA levels of igf-1 and igf-2 in vitro, which showed that they have similar physiol. functions.Taken together, the biol. active recombinant tongue sole IGF-I and IGF-II proteins will allow us to further investigate their physiol. roles in growth regulation of this species.Furthermore, the present results also hinted at the potential application of these two recombinant IGF-I and IGF-II proteins into the tongue sole farming industry.