Use of Amazonian Mauritia flexuosa fruit pulp as chemoprotectant against ammonia and nitrite toxicity to juvenile shrimps Litopenaeus vannamei

This study investigated the effects of the ammonia and nitrite toxicity in shrimp Litopenaeus vannamei juveniles fed diets containing Amazonian Mauritia flexuosa fruit pulp. The post-larvae (PL) shrimps (weight 5.0 ± 0.3 mg) were fed with five diets (36% protein, 10% lipid), containing 0 (Control group), 1.25, 2.50, 5.00, and 10.00% (W/W) of M. flexuosa fruit pulp inclusion (1 shrimp L-1, tank of 100 L, treatments in triplicate) for 43 days. After this period, the juvenile shrimps (weight 396.00 ± 0.35 mg) were randomly distributed among 30 tanks with 30 L of useful volume, containing 20 shrimps per tank and exposed (96 h) to ammonia (0.48 mg NH3-N L-1) and nitrite (40 mg NO3 L-1) toxicity, in triplicate. Measured variables were the total antioxidant capacity (ACAP), lipid peroxidation (TBARS), reduced glutathione (GSH) levels and concentration of protein sulfhydryl groups (P-SH). The results indicated a significant increase (p<0.05) in ACAP, when shrimps were fed 2.50 and 5.00% (ammonia exposure), or 5.00 and 10.00% (nitrite exposure) of M. flexuosa inclusion. Similarly, lipid peroxidation levels were lower (p<0.05) in shrimps exposed to ammonia or nitrite and fed the inclusion of 2.50-10.00% of M. flexuosa in the diet. The GSH levels increased (p<0.05) in shrimps that were exposed to ammonia and fed 10% of M. flexuosa. However, there was no significant difference (p>0.05) in the P-SH levels, after both ammonia and nitrite exposure. It was concluded that the use of Mauritia flexuosa improves the resilience of Litopenaeus vannamei to cope with ammonia and nitrite toxicity and indicates its use as a chemoprotectant against toxic nitrogenous compounds. Particularly, the conspicuous TBARS reduction after nitrite exposure and augmented GSH levels in ammonia-exposed shrimps previously supplemented with M. flexuosa fruit pulp suggest a hormetic response.

本研究探究了投喂含亚马逊扇叶糖棕（Mauritia flexuosa）果肉日粮的凡纳滨对虾（Litopenaeus vannamei）幼体在氨氮与亚硝酸盐胁迫下的毒性响应。初始体重为5.0±0.3 mg的凡纳滨对虾仔虾后期（PL）被分为5组，饲喂粗蛋白36%、粗脂肪10%的基础日粮，其中分别添加0（对照组）、1.25、2.50、5.00及10.00%（重量/重量比）的扇叶糖棕果肉，养殖密度为1尾·L⁻¹，养殖缸体积100 L，每组设置3个生物学重复，养殖周期为43天。养殖周期结束后，幼体体重达396.00±0.35 mg，将其随机分配至30个体有效容积30 L的养殖缸中，每缸放养20尾对虾，随后进行96 h的氨氮（0.48 mg NH₃-N·L⁻¹）与亚硝酸盐（40 mg NO₃·L⁻¹）胁迫处理，每组设置3个生物学重复。本次试验测定的指标包括总抗氧化能力（ACAP）、脂质过氧化（TBARS）、还原型谷胱甘肽（GSH）水平以及蛋白质巯基（P-SH）浓度。结果显示：在氨氮胁迫组中，投喂2.50%与5.00%扇叶糖棕果肉日粮的对虾总抗氧化能力显著升高（p<0.05）；在亚硝酸盐胁迫组中，投喂5.00%与10.00%扇叶糖棕果肉日粮的对虾总抗氧化能力同样显著提升（p<0.05）。类似地，投喂2.50%~10.00%扇叶糖棕果肉日粮的对虾，其脂质过氧化水平在氨氮或亚硝酸盐胁迫下均显著降低（p<0.05）。此外，氨氮胁迫且投喂10%扇叶糖棕果肉日粮的对虾，其还原型谷胱甘肽水平显著升高（p<0.05）。然而，无论经氨氮还是亚硝酸盐胁迫，对虾的蛋白质巯基浓度均无显著差异（p>0.05）。研究表明，添加扇叶糖棕果肉可提升凡纳滨对虾应对氨氮与亚硝酸盐毒性的抗逆能力，提示其可作为抗含氮有毒化合物的化学保护剂。尤其值得关注的是，亚硝酸盐胁迫下对虾的TBARS水平显著降低，且氨氮胁迫下预先投喂扇叶糖棕果肉的对虾GSH水平升高，这一结果提示存在毒物兴奋响应（hormetic response）。