Abstract:The directly stimulating actions of salmon GnRH analog sGnRH-A (Arg6TrP7Lou8Pro9NEt--LHRH) and mammalian GnRH analog LHRH-A(Ala6Pro9NEt--LHRH) on growth hormone (GH) secretion from pituitary of com-mon carp (Cyprinus carpio L.), and the effects of LHRH-A and sGnRH-A on se-rum GH levels and growth of grass carp fingerling were studied by using an invitro perifusion system and in vivo treatment respectively. Two--min pulses ofsGnRH--A or LHRH-A (1, 10 and 100nM), in dose-dependent manner, directlystimulated GH secretion from perifused pituitary fragments of common carp. Thein vitro GH-releasing potency of each dose of sGnRH--A was significantly higherthan that of the same dose of LHRH--A. Intraperitoneal injection of sGnRH--A or LHRH--A(0. 01μg/g,b.w./week and 0. 001μg/g, b.w./week, once a week, total of sixweeks) resulted in significant increase in relative somatic growth rate (RSGR)and relative linear growth rate (RLGR) and in increase in serum GH levels ofgrass carp fingerling. The inductions of LHRH-A and sGnRH--A on growth ofgrass carp fingerling were dose--dependent, and the increases in RSCR andRLGR induced by sGnRH-A were significantly higher than those induced byLHRH-A. These results indicated that GnRH analog can directly stimulate GHsecretion from pituitary and induce increase in growth rate of cultured fish. Therelationships between structure and function of GnRH analog in inducing GHsecretion and grewth are similar to those in stimulating gonadotropin secretionin teleost.