Dietary glycerol supplementation in aquaculture feed is seen as an alternative and inexpensive way to fuel fish metabolism, attenuate metabolic utilization of dietary proteins and, subsequently, reduce nitrogen excretion. In this study, we evaluated the impact of dietary glycerol supplementation on nitrogen excretion of European seabass (Dicentrarchus labrax) and its effects on metabolite profile and bacterial community composition of gut digesta. These effects were evaluated in a 60-day trial with fish fed diets supplemented with 2.5% or 5% (w/w) refined glycerol and without glycerol supplementation. Nuclear magnetic resonance spectroscopy and high-throughput 16S rRNA gene sequencing were used to characterize the effects of glycerol supplementation on digesta metabolite and bacterial community composition of 6-h postprandial fish. Our results showed that ammonia excretion was not altered by dietary glycerol supplementation, and the highest glycerol dosage was associated with significant increases in amino acids and a decrease of ergogenic creatine in digesta metabolome. Concomitantly, significant decreases in putative amino acid degradation pathways were detected in the predicted metagenome analysis, suggesting a metabolic shift. Taxon-specific analysis revealed significant increases in abundance of some specific genera (e.g., Burkholderia and Vibrio) and bacterial diversity. Overall, our results indicate glycerol supplementation may decrease amino acid catabolism without adversely affecting fish gut bacterial communities.Key points• Glycerol can be an inexpensive and energetic alternative in fish feed formulations.• Glycerol did not affect nitrogen excretion and gut bacteriome composition.• Glycerol reduced uptake of amino acids and increased uptake of ergogenic creatine.• Glycerol reduced putative amino acid degradation pathways in predicted metagenome.

中文翻译：

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甘油饲料补充剂对鲈鱼代谢和肠道微生物群的影响。

在水产养殖饲料中添加膳食甘油被视为一种替代且廉价的方式来促进鱼类代谢，减弱膳食蛋白质的代谢利用，从而减少氮的排泄。在这项研究中，我们评估了膳食甘油补充剂对欧洲鲈鱼（Dicentrarchus labrax）氮排泄的影响及其对肠道消化物代谢物谱和细菌群落组成的影响。这些影响在一项为期 60 天的试验中进行了评估，鱼饲饲料添加了 2.5% 或 5% (w/w) 精制甘油，但不添加甘油。使用核磁共振波谱和高通量 16S rRNA 基因测序来表征补充甘油对餐后 6 小时鱼的食糜代谢物和细菌群落组成的影响。我们的结果表明，膳食甘油补充剂不会改变氨的排泄，并且最高的甘油剂量与氨基酸的显着增加和食糜代谢组中肌酸的减少有关。同时，在预测的宏基因组分析中检测到假定的氨基酸降解途径显着减少，表明代谢转变。特定分类群的分析揭示了一些特定属（例如伯克霍尔德菌属和弧菌属）的丰度和细菌多样性的显着增加。总体而言，我们的结果表明，补充甘油可能会降低氨基酸分解代谢，而不会对鱼肠道细菌群落产生不利影响。关键点• 甘油是鱼饲料配方中一种廉价且充满活力的替代品。