Abstract:Aiming at exploring the sequence differences of IGFⅠ gene of Nile tilapia (Oreochromis niloticus NewGifts,ON), blackchin tilapia (Sarotherodon melanotheron,SM) and their First Generation of Hybrid (HB), investigating the relationships between the great differences of saltresistant property among the three genotypes, we cloned partial cDNA fragments of insulinlike growth factor Ⅰ(IGF-Ⅰ) from gill extracts through rapid amplification of 3′ cDNA ends(3′RACE)methods. The results demonstrated to be the IGF-Ⅰb gene cDNAs with length of 1 076 bp,1 075 bp and 1 079 bp respectively and comprising of a stop codon, a 546 bp open reading frame (ORF) encoding a 182 amino acid peptides(aa), and 3′untranslated regions(3′UTR). The deduced amino acid sequence of IGF-Ⅰb precursor is composed of signal peptide, mature peptide(including conserved B, C, A and D domains consisting of 29aa,10aa,21aa and 8aa respectively)and E domain of 70aa. Results of the predicted secondary structures were typed as “mixed patterns”. The results of multiple alignments showed highly homologous with 75.8% to 100% amino acid identity. The B and A domains are highly conserved in all of the allied species. There are 2aadeletion between No.82 and 83 sites in C domain, 3aa and 1aadeletion next to NO.131 and No.159 site, respectively. Ala / Pro substitution occurred at No.133 of E domain of blackchin tilapia compared with ON and HB, which is identical to Oreochromis mossambicus and Oreochromis urolepis hornorum. We presumed that the differences of saltresistant property of ON, SM and HB may be due to the alterative splicing of the IGF-Ⅰ E domain.