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The objective of this study was to evaluate the chronic effect of different nitrate concentrations on the zootechnical performance and welfare of Macrobrachium amazonicum juvenile. A randomized bioassay was conducted over 28 days, with four treatments (0, 8, 16, and 32 mgL−1 N-NO3−) and four replicates. The prawns (0.52 ± 0.09 g) were stocked (n = 12 per experimental unit) in a semi-static system with daily renewal of 90% of the usable volume. At concentrations from 0 to 16 mgL−1 nitrate, average survival was above 80%, and total average biomass above 6 g; at 32 mgL−1 nitrate, average survival was 27%, and total average biomass 2 g. Nitrate concentration was significantly negatively correlated with mean total final length, mean final weight, specific growth rate, mean antenna length, and the gill condition by Organ Index. Reductions in growth rate of 34% and 45% were observed in the treatments of 16 mgL−1 and 32 mgL−1 nitrate, respectively. In the histological analysis of the gills, increasing nitrate concentration led to symptoms ranging from mild inflammatory processes to severe regressive and progressive damage, including necrosis, hyperplasia, and edema. We conclude that concentrations up to 8 mgL−1, over a 28-day exposure period, are acceptable for nursery stages in the intensive production of M. amazonicum. |
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