Changes in heart rate and respiratory rate were investigated when carp were stimulated by various stress simulations. A radiotelemetry transmitter was chronically implanted into the peritoneal cavity of the adult carp. The carp were reared in individual glass tanks under a 12h/12h light-dark cycle, and the water temperature was kept at 25°C. The carp were stressed by the tapping with the fingers on the side of the glass tank, and the light suddenly being turned off or on in the daytime. By tapping, HR decreased transiently and recovered thereafter. HR also deceased after the light was suddenly turned both off and on. The rhythm of respiratory movement was different from that of the heart beat. The stress simulation (tapping, the light being turned off and on) induced a decrease in respiratory movement. The inhibitory effects of such stress stimulation on heart beat and respiratory movement were prominent for about 10 seconds just after beginning the stimulation, and the an inhibitory effect remained for a few minutes. After the intraperitoneal administration of atropine sulfate 1mg/kg, the inhibitory effect on heart beat due to this stimulation disappeared, while the inhibitory effect on the respiratory movement remained. From these results, it is suggested that when stress simulations received by the brain, the heart beats and respiratory movements are inhibited via the different nervous pathways, and that inhibitory stress response on heart beat may be mainly mediated by cholinergic vagal nerves in carp. [Jpn J Physiol 55 Suppl:S229 (2005)]