Our increased dependence on cultured as opposed to wild stocks of fish as a dietary source of protein has necessitated steps to control reproduction of fish as many species fail to ovulate under captive conditions. Some fish species exhibit a protracted breeding season and it is desirable to control the timing and synchrony of breeding to increase the efficiency of aquaculture operations. Historically, fish culturists have relied upon the administration of fish pituitary extracts, or in certain cases mammalian gonadotropin preparations to induce ovulation [1]. More recently, efforts have been made to substitute the use of LHRH peptide hormones for the more expensive pituitary hormone preparations. Since the first demonstration that LHRH stimulates gonadotropin (GtH) release from carp pituitaries invitro [2], there have been numerous reports showing that LHRH-and LHRH analogs stimulate GtH release in a variety of teleosts [3–5]. To date, the use of these compounds to regulate fish reproduction has met with varied success. In recent studies it has been demonstrated that distinct forms of LHRH are present in submammalian vertebrates [6] and these findings have opened new avenues of research investigating the use of fish, bird and mammalian LHRH analogs for the hormonal control of reproduction of fish in aquaculture [7–8].