Juvenile rainbow trout (Salmo gairdneri) conditioned to traverse a 2.4-m-long channel to receive a food reward where subjected to in-transit thermal challenges. Conditioning was to a criterion that required 80% of the fish to leave the 'home' area and reach the 'reward' area within 2 minutes of release. Challenges were at successive 3C increments above acclimation or the previous challenge temperature. Fish were first observed to delay their entrance into the intervening heated water at challenge temperatures of 12-15C above acclimation. Above their critical thermal maximum (CTM) the reward was achieved even at the expense of deaths among the achievers. Responses were the same whether fish were challenged individually or as groups.