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

Abstract

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.