Swimming speed and activity costs of dace (Phoxinus eos × P. neogaeus) were estimated in the field using underwater video cameras. Activity costs were estimated by converting swimming speeds and the number of movements into swimming costs. Average swimming speed ranged from 6.7 to 12.2 cm.s−1across 2 h periods and varied significantly among dates and time of day. The time spent swimming by dace ranged from 616 to 17 640 s 2 h−1. Activity costs per 2h period ranged from 2.1 to 4O.2J 2h−1and were strongly correlated to the time spent swimming. Daily activity cost estimated using the cameras averaged 128.9J day−1and was equivalent to 1.7 times the standard metabolic rate. Activity cost predicted using a bioenergetic model in conjunction with independent estimates of consumption and growth rates averaged 138.8J day−1. This study indicated that swimming characteristics and activity costs of dace varied significantly both within and among days. These analyses also indicated that equally valid activity costs for fish in the field can be estimated using video cameras and the difference between Consumption and gr