two trials were set up to evaluate the influence of different levels of dietary vitamin c supplementation on growth, performance, survival rate and resistance to low dissolved oxygen (lodo) concentration of piau？u fingerlings (leporinus obtusidens). trial 1 (105 days) evaluated the effect of diet supplementation with l-ascorbic acid (0, 50, 150, 250, 350, 450, 550, 650, 750, 850 mg of vitamin c/kg of diet) on weight gain and survival, in a completely randomized design. there was no significant differences among treatments with respect to weight gain (p > 0.4054) and survival rate (p > 0.5657). in trial 2, groups of 10 fish of each replicate of trial 1, were stocked in 20-l cages, in a randomized block design, and submitted to a 14-h lodo stress (1.0 mg do/l). fingerling survival rate was not significantly affected by lodo levels (p > 0.4032) up to 14 hours after stressing conditions ceased. in contrast to our results, data found in the literature show that dietary vitamin c supplementation significantly affects the studied parameters. therefore, it is suggested that more extensive studies should be performed to determine dietary vitamin c requirements of this species.