Glutamine and arginine in diets for Nile tilapia: Effects on growth, innate immune responses, plasma amino acid profiles and whole-body composition

Glutamine (Gln) and arginine (Arg) are functional amino acids (AA) known to improve growth, immunity and nutrient utilization of animals. Juvenile Nile tilapia were fed six experimental diets formulated to contain different levels of supplemental Gln and/or Arg (Control, GLN 1%, GLN 2%, ARG 1%, ARG 2% and GLN + ARG 1%) for a 9-week period. Growth performance, innate immune responses, AA profiles in plasma and whole-body were examined. Dietary Gln and/or Arg supplementation resulted in significant effects on weight gain, feed intake, feed efficiency, protein efficiency and protein retention. Moreover, the concentration of free AAs in plasma at 6 h and 18 h were significantly affected by experimental diets. The AA concentrations significantly affected at the 6 h sampling were Cys, Asp, Ser, Gly and Hyp while at 18 h, differences were observed for Arg, Val, Cys, Ser, Gly and Pro. In contrast, only differences in Gln, Gly and Ser concentrations were observed regarding AA composition of the whole-body tissues. Therefore, the AA profiles of plasma were more affected by the dietary GLN and/or ARG supplementation than whole-body. Most of the immunity indicators were not raised by dietary levels of Gln and/or Arg probably as a reflection of the non-activated state of the immune cells. Although Gly was included to the experimental diets to adjust nitrogen content, this inclusion resulted in effects on the growth performance and physiological parameters. Finally, Nile tilapia fed the combined supplement of GLN + ARG at 1% had more improved growth performance than those fed the diets supplemented individually with Gln or Arg.