Arginine supplementation in plant‐rich diets affects growth, feed utilization, body composition, blood biochemical indices and gene expressions of the target of rapamycin signaling pathway in juvenile Asian red‐tailed catfish (Hemibagrus wyckoiides)

Arginine (Arg) is an important essential amino acid required for optimum fish growth. However, its role in plant-rich diets on growth and the required level in juvenileHemibagrus wyckioidesare currently unknown. This study evaluated the effects of Arg supplementation in plant-rich diets on growth, feed utilization, whole body composition, blood biochemical indicators and gene expressions of the target of rapamycin (TOR) signaling pathway in juvenileH. wyckioides. A total of 450 fish (6.40 +/- 0.06 g) were randomized into six equal groups and fed on diets with graded Arg levels: 0 (control), 3, 6, 9, 12 and 15 g/kg of dry feed for eight weeks. The results revealed that specific growth rate (SGR) and feed conversion ratio of juvenileH. wyckioideswere significantly improved and reduced, respectively in fish fed on 9 g/kg of Arg supplementation (p < .05). The optimum amount of dietary Arg content in plant-rich diets forH. wyckioideswas 63.77 g/kg diet based on SGR. Feeding fish with dietary Arg supplementation ranging from 9 to 12 g/kg improved significantly (p < .05) whole body protein contents and decreased lipid deposition. The mRNA levels of TOR, eukaryotic translation initiation factor 4E (4EBP) and ribosomal protein S6 kinase 1 (S6K1) in muscle and liver were significantly affected by increasing dietary Arg levels. Meanwhile, the mRNA relative expression levels of TOR and S6K1 in the liver and muscle increased significantly as Arg supplementation increased. On the other hand, the mRNA relative expression levels of 4EBP was significantly higher in fish fed on the 9 g/kg Arg diet compared to those fed on the control and 15 g/kg Arg diets. In conclusion, our current results indicate that dietary Arg supplementation in plant-rich diets, might activate the TOR signaling pathway, which promotes protein synthesis and reduces lipid accumulation ofH. wyckioides, resulting in improved growth.