Rotifer Brachionus rotundiformis is the first live food for larval fish that can generally be plagued by ammonia (AC) in intensive culture systems. Ammonia accumulates enough to cause rotifer death. L-carnitine (LC) as a supplement of a vitamin-like nutrient can ameliorate rotifer growth performance and reproduction. The present study investigated the effects of LC on growth performance, antioxidant enzymatic activity, bacterial numbers and eradication of AC toxicity in rotifer. During a 7-day culture experiment added different concentration LC, Acute toxicity tests of AC and a batch culture experiment treated with LC and AC were performed. The results indicated that suitable LC concentration (1−100 mgL⁻¹) treatment promoted significantly the rotifer population growth, while the AC was opposite and the AC median lethal concentration (LC₅₀)-24 h was 12.24 mg L^-1. Batch culture results showed that, under AC stress, LC significantly increased the rotifer population density and egg rate, and reduced rotifer malondialdehyde (MDA) level, increased rotifer Superoxide dismutase (SOD), Catalase (CAT), glutathione peroxidase (GPx) and total antioxidant capacity (T-AOC) activities. For the bacterial numbers, all treatments presented an increasing trend during the culture period, and there was a significant correlation with the rotifer population density especially in the group LC + AC. Overall, our results indicate that the rotifer growth can be inhibited by the AC, and under AC stress, LC can also improve the population growth, anti-stress ability of rotifer and the bacterial numbers in the medium. The amelioration of rotifer-growth may be linked to the anti-stress ability and the bacterial numbers.

轮虫Brachionus rotundiformis是幼虫鱼的第一种活食，在集约化养殖系统中通常会受到氨（AC）的困扰。氨积累足以引起轮虫死亡。左旋肉碱（LC）作为维生素样营养素的补充，可以改善轮虫的生长性能和繁殖能力。本研究调查了LC对轮虫生长性能，抗氧化酶活性，细菌数量和根除AC毒性的影响。在为期7天的培养实验中，添加了不同浓度的LC，进行了AC的急性毒性测试以及用LC和AC处理的分批培养实验。结果表明合适的LC浓度（1-100 mgL ^-1）处理显着促进轮虫种群增长，而AC相反，AC致死浓度（LC ₅₀）-24 h为12.24 mg L ^-1。批量培养结果表明，在交流胁迫下，LC显着提高了轮虫种群密度和卵率，降低了轮虫丙二醛（MDA）水平，增加了轮虫超氧化物歧化酶（SOD），过氧化氢酶（CAT），谷胱甘肽过氧化物酶（GPx）和总抗氧化能力（T-AOC）活性。就细菌数量而言，所有处理在培养期间均呈现增加趋势，并且与轮虫种群密度显着相关，尤其是在LC + AC组中。总体而言，我们的结果表明，AC可以抑制轮虫的生长，在AC胁迫下，LC还可以改善种群增长，轮虫的抗应激能力以及培养基中细菌的数量。轮虫生长的改善可能与抗应激能力和细菌数量有关。