161 Aquaculture, 59 (1986) 161-168 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands Technical Paper Technique for Making Chronic-Release LHRH-a and 17z-Methyltestosterone Pellets for Intramuscular Implantation in Fishes C.-S. LEE, C.S. TAMARU and C.D. KELLEY Oceanic Institute,Makapuu Poir t, Waimanalo, HI 96795 (U. S.A.) (Accepted 14 July 1986) ABSTRACT Lee, C.-S.. Tamaru, C.S. and Kelley, C.D., 1986. Technique for making chronic-relea3e LHRH-a and 17a-methyltustosterone pellets for intramuscular implantation in fishes. Aquat ulture, 59: 161-168. Interest in stimulating vitellogenesis in commercially important fishes has led to the use of implantable chronic-release cholesterol pellets and silastic capsules containing LHRH-a and 17a- methyltestosterone, respectively. A detailed description of how these implant3 are made is provided. INTRODUCTION For a number of years, there has been interest in developing techniques using hormones to induce or accelerate vitellogenesis in commercially important fish species (reviewed by Lam, 1982). This stage of oocyte maturation can be of considerable duration, in some cases, months, and has been shown to be dependent on elevated pituitary gonadotropin (GtH) and gonadal steroid lev- els (reviewed by Ng and Idler, 1983). Satisfactory replication or augmentation of these hormone profiles, in order to stimulate vitellogenesis, has proven dif- ficult. This is due in part to their chronic nature. Repetitive injections have caused gonadal atresia and even dath in species sensitive to stress (Lam, 1982). Alternative methods for chronic delivery of hormones have been re\ ie-ved by Crim (1985). Continuous administration of exogenous GtH may result in an undesirable antibody reaction (Lam, 1D82; Crim et al., 1983a). This potential pioblem can be avoided by using a GtH-releasing horiaone such as LHRH or one of its superactive analogues, LHRH-a. However, with its rel- atively short half-life (Kent ef al., 1980), LHRH-a must be introduced fre- quently into the fish's circulation to effect a chronically elevated GtH profile. LHRH (Windholz et al., 1983), and presumably LHRH-a, are rendered inac- 0044-8486/86/$03.50 © 1986 Elsevier Science Publishers B.V.