Exposure of Macrobrachium rosenbergii (De Man, 1879) post-larvae to different nitrate concentrations: Effect on performance and welfare

The present study aimed to determine the effect of acute and chronic exposure to nitrate on the zootechnical performance and welfare of Macrobrachium rosenbergii post-larvae. In order to assess acute nitrate toxicity, M. rosenbergii post-larvae (n = 280) were exposed to seven concentrations in quadruplicate (0, 10, 50, 100, 200, 400, and 800 mg L-1 N-NO3-) for 96 h. The results showed LC50 values for 24, 48, 72, and 96 h of approximately 352, 192, 114, and 87 mg L-1 nitrate, respectively. The safety level (SL) of nitrate was estimated at 8.62 mg L-1. Chronic toxicity was assessed based on the SL established during the acute test. The chronic experimental design comprised five treatments and three replicates, namely, control (no nitrate - 0 mg L-1), half the SL (4.5 mg L-1), the SL itself (9 mg L-1), twice the SL (18 mg L-1), and four times the SL (36 mg L-1), with the post-larvae (n = 400) being exposed for 24 days. By the end of the experiment, survival, weight, length, final biomass, antenna length, and scaled mass index (SMI) were assessed. The chronic toxicity test showed a negative trend in survival and biomass with reductions from 89 to 28% and 0.72 to 0.23 g, respectively, as concentration increased from 0 to 36 mg L-1. A significantly negative effect was also observed for weight (0.036 to 0.019 g), total length (1.72 to 1.36 cm), and mean antenna length (2.32 to 1.72 cm) (F = 6.18; P = 0.00013). The SMI was also impacted by the increase in nitrate concentration. It can be concluded that concentrations above 4.5 N-NO3- (half the safety level) are not recommended for the production of M. rosenbergii post-larvae.