Insulin-like growth factor (IGF) system consists of three ligands (IGF-1, IGF-2, most recently IGF-3), two receptors (IGF-1R, IGF-2R) and six IGF binding proteins (IGFBPs). Reproduction and growth, the most basic characteristics of organisms, are closely related to and distinguished from each other. IGFs are the key factors that regulate growth and reproduction axis. Recent researches have shown that gonadal development and maturation are associated with cell differentiation and tissue growth, and that traditional growth factors IGF-1, IGF-2 and a recently discovered IGF subtype (IGF-3) play an important role in fish gonad. The present review emphasizes the structure of IGF-3, a fish gonad-specific IGF, and IGF signal pathway as well as its potential physiological functions in fish gonad.