Traditional hatcheries raise fish in featureless environments and subject them to dull routines, whereas new, experimental hatcheries raise fish in visually stimulating environments with varied routines. When released into the wild, fish from the experimental hatcheries are bolder than those from traditional hatcheries in exploring new environments and trying new types of food. Fish raised in the experimental hatcheries, ttherefore, are more likely to survive after their release. Which one of the following is an assumption required by the argument? ["The quality of the environments into which hatchery-raised fish are released has little effect on the fish's survival rate.", 'Some fish raised in traditional hatcheries die because they are too timid in their foraging for food.', 'It is economically feasible for hatchery operators to expose fish to greater visual stimulation and to more varied routines.', 'Fish in the wild always live in visually stimulating environments.']