AbstractA single heat shock of 28°C for 10 min, applied 15 min after water activation to five different batches of brown trout,Salmo truttaL., ova and replicated within one batch produced triploid rates ranging from 22% to 100% and variable survival to hatch ranging from 9.4% to 47.9%. Variability was greater among batches than among replicates. In general, the treatment reduced survival to hatch by 50%. The range of triploid yields obtained from a single heat shock regime is discussed in terms of potential advantages to aquaculture