Recirculating aquaculture systems typically require water changes to reduce nitrate levels and prevent toxicity. The Delta Smelt (Hypomesus transpacificus) exists almost exclusively in freshwater culture, so knowledge of its nitrate sensitivity is critical. Here we quantified the acute (4 d) and chronic (30 d) toxicity of nitrate to Delta Smelt. In the acute test, Delta Smelt exhibited no mortality at concentrations up to 1000 mg L-1 nitrate. In the chronic test, Delta Smelt exhibited elevated liver glycogen depletion at 1000 mg L-1, gill aneurisms at ≥500 mg L-1, gill ionocyte hyperplasia at ≥250 mg L-1, and no negative effects at ≤125 mg L-1. We detected no differences among treatments in condition factor, hepatosomatic index, or liver glycogen (measured biochemically) up to 1000 mg L-1 nitrate, although the sample means were all relatively low at 500 and 1000 mg L-1. We therefore recommend that managers do not exceed 125 mg L-1 nitrate for more than 30 d (28 mg NO3-N L-1), the No Observed Effect Concentration (NOEC). Overall, Delta Smelt are relatively tolerant to nitrate compared to freshwater fishes, likely reflective of the species’ marine ancestry and euryhaline life-history.