Nitrate toxicity in Siberian sturgeon (Acipenser baeri)

Excess nitrate in aquaculture has traditionally been reduced by water exchange. Current trends in environmental regulation, however, are limiting the amount of water which may be consumed or discharged, reducing the ability to use large influxes of water to remediate excess nitrate. This will create significant challenges for the aquaculture community, as the etiology, effects and tolerable thresholds of nitrate are relatively unknown in fishes as compared to ammonia and nitrite. Three 96-h LC50 tests were conducted using 6.9 ± 0.31 g, 66.9 ± 3.4 g, and 673.8 ± 18.6 g Acipenser baeri, to determine baseline information regarding the sensitivity of this species to elevated nitrate as compared to other species, and determine if sensitivities are mediated by size. The 96-h LC50 results for nitrate-N for 6.9 ± 0.31 g, 66.9 ± 3.4 g and 673.8 ± 18.6 g fish were 1028 mg/l, 601 mg/l and 397 mg/l, respectively, indicating an increased susceptibility to nitrate with increasing size. Predictions of susceptibilities for larger animals based on linear extrapolation of the current data is also discussed. These findings reveal that nitrate may be a considerable concern for Siberian sturgeon reared in recirculating systems with limited water exchange.