Gilderhus, P. A., 1990, Benzocaine as a fish anesthetic: Efficacy and safety for spawning-phase salmon: The Progressive Fish Culturist, v. 52, no. 3, p. 189-191. Abstract: The anesthetic benzocaine was tested for efficacy and safety for spawning-phase chinook salmon (Oncorhynchus tshawytscha ) and Atlantic salmon (Salmo salar ) at federal fish hatcheries. Benzocaine concentrations of 25-30 mg/L anesthetized most fish in less than 3.5 min, and most fish recovered in less than 10 min after 15 min of exposure. Safety margins were narrow; both species tolerated 30 mg/L for about 20 min, but 25 min of exposure caused deaths. For 15-min exposures, concentrations of 35 mg/L for chinook salmon and 40 mg/L for Atlantic salmon were lethal. Keywords: fish-culture, hatcheries, anaesthetics, toxicity-tolerance, Oncorhynchus-tshawytscha, Salmo-salar, spawning-; benzocaine-