L-carnitine can improve the population growth and anti-stress ability of rotifer (Brachionus rotundiformis) under ammonia stress

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.