Prolactin (PRL) is a 198 amino acid long polypeptide hormone, structurally similar to growth hormone, secreted by adenohypophysis in the vertebrates. The full-length amino acid sequence of PRL has been determined from a variety of teleost and non-teleost fish. Teleost PRL genes are shorter than mammalian. PRL exists in two forms, namely, PRL-1 commonly found in all vertebrates and PRL-2 found in several non-mammalian vertebrates including fish. This hormone binds to transmembrane Prolactin receptor (PRLR) which is a member of the class 1 cytokines receptor superfamily. We know that PRL has over 300 different functions in vertebrates. In fish, PRL plays an important role in migration, osmoregulation, parental behaviour, reproduction and development along with other hormones. Recent studies show prolactin has a role in cell proliferation in the gills of teleost fish. This review highlights diversified role of PRL in fish which may serve as avenues for further researches in near future.