The characteristics and ontogeny of the startle response to various stimuli of laboratory-reared coho salmon were studied with high-speed cinematography. Dechorionated embyros did not exhibit a startle response to electrical stimulation; however, at hatching, the startle response could be provoked consistently (> 90% response) with electrical stimulation. After hatching, the kinematics of the startle response remained unchanged as the fish grew but the velocities attained during the response increased. The percentage of fish responding with a startle response to visual, tactile, and acoustico-lateralis stimuli was low (0–20%) at hatching, but after 3 weeks at 2°C, 50% of the fish tested exhibited a startle response to acoustico-lateralis stimulation. At this time, only 20–25% of the fish tested responded to tactile stimulation. The response to visual stimulation increased slowly up to emergence but at emergence (8 weeks after hatching) the percentage of fish responding to visual stimulation increased sharply to 75%.