An average of 8.9 million trout (Oncorhynchus spp., Salmo trutta, Salvelinus spp.) were planted in Wyoming each year from 1987 through 1990; 86% were of subcatchable size (<8.25 in) and 14% were of catchable size (≥8.25 in). Of the total fish planted, 1.9 million subcatchable trout and 177,000 catchable trout were planted in streams. Harvest rates of trout stocked in streams was low (average, 5.7%), possibly because of the hatchery conditions under which they were reared. Hatchery-reared trout were raised in conditions far different from those of natural waters: densities hundreds of times those in the wild, nearly constant water flow and water temperature, regular feeding, lack of cover, and absence of predators. Hatchery trout may become disoriented, fail to seek cover, forage inefficiently, and die when planted in streams with competing fish. Evaluating the survival of hatchery trout fed natural food, rearing hatchery trout in simulated natural conditions, raising them at moderate densities, and evaluating costs associated with management of wild and hatchery trout would provide additional means for judging the potential to train hatchery trout to survive in the wild. Such evaluations also would provide more criteria upon which to judge the success of planting hatchery trout.
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Wiley et al. (1993) studied this question.