Development of LHRH-a Copolymer Pellet Polymerized by Ultraviolet and Its Application for Maturation in Red Sea Bream Pagrus major during the Non-Spawning Season

A method is described for preparing a nonbiodegradable copolymer pellet containing luteinizing hormone-releasing hormone analogue (LHRH-a), des Gly¹⁰-[D~Ala⁶] LHRH ethyl-amide, polymerized by ultraviolet rays to produce sustained hormone release. The pellet was applied to induce gonadal development and maturation in red sea bream Pagrus major during the non-spawning season, from November to December. Single implantation of a copolymer pellet containing 100 jug LHRH-a induced gonadal development and spawning in completely immature fish 18 days after implantation, about six months prior to the nutural spawning season. Fish implanted with a 50 fig LHRH-a copolymer pellet or a control pellet were not induced to spawn. The histopathological findings of muscular tissues surrounding the implant showed that no inflammatory response to a foreign body appeared even one month after implantation. Results from the present study indicate that the LHRH-a copolymer pellets prepared by us have several features: (1) the pellets can be prepared easily and mass-produced at one time, (2) the pellets are useful for long-term hormone therapy in inducing sexual maturation in fish requiring a series of hormone treatments, and (3) the copolymer has good biocompatibility. However, the fertility rates of eggs produced were low. Further investigation is necessary to devise an effective method for obtaining more viable eggs by the use of copolymer pellets.