On the basis of species discrepancies of responsiveness to LRH--A, serum gonado-tropin (sGTH) levels of the mature female carps and immature female silver carpwere compared after cardiac injections of LRH-A at two different timos of a day.Fish sera were sampled at intervals either within 1 hour or during a 24--hour period.The sGTH concentration was measured by radioimmunoassay. In all cases, dealingwith the mature fish held under 18--20℃ two distinguished peaks were observed,one within 5 minutes and the other 5--6 hours later. The second peak was notdetectable in immature fish. This may signify that the second surge of GTH was moreimportant than the first in inducing spawning. When carp was subjected to lowertemperatures (11-13.5℃), the occurrence of the peaks was much delayed, which is inaccordance with the fact that when water temperature drops down beyond optimum,the response to the analogue is prolonged or even suppressed as has been found in farmpractice. When silver carps receiving LRH-A 23 days after the first ovulation which wasinduced by the same hormone analogue, the sGTH pattern was similar but higher in magnitude. Anatomical examination showed that ovaries had significantly proceededto the IV stage of maturation. though the GSI values were lower than that prior to thefirst ovulation. The long-term effect of LRH--A in terms of acceleration of ovarianrecrudescence in the postspawning phase of the reproductive cycle was apparent.