Guanidinoacetic Acid Significantly Improves Growth, Antioxidant Capacity, and Nonspecific Immunity for Juvenile <i>Litopenaeus vannamei</i>

Guanidinoacetic acid (GAA)-a nutritional additive-is essential for the healthy growth of aquatic animals. The experiment was conducted to examine the effects of dietary GAA on growth, muscle amino acid composition, antioxidative indices, and nonspecific immunity for juvenile <i>Litopenaeus vannamei</i>. Total 800 healthy shrimp (initial mean weight = 0.27 ± 0.03 g) were equally distributed into 15 tanks (0.3 m³; five groups, and three repeats per group) and fed with diets containing GAA levels (e.g., 0, 0.04%, 0.10%, 0.13%, and 0.16%, named G0, G004, G010, G013, and G016, respectively) for 8 weeks (four times a day). At the end of the trial, shrimps from all replicate groups were weighed, and serum, hepatopancreas, and muscle were collected from three random tails. The weight gain rate (WGR) and specific growth rate (SGR) were significantly higher, and feed conversion rate (FCR) was significantly lower in G010 and G013 groups than in G0 group. No significant effect of GAA on the total amino acids of each treatment was observed. Serum superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) were significantly higher, and malondialdehyde (MDA) levels were significantly lower in G010, G013, and G016 groups compared to G0 group. Alkaline phosphatase (AKP), phenoloxidase (PO), lysozyme (LZM), and acid phosphatase (ACP) activities were significantly higher in G010, G013, and G016 groups than in G0 group. The mRNA expressions of immune deficiency (<i>imd</i>) and <i>lzm</i> genes in G010 and G013 groups were significantly upregulated. Following the challenge with <i>Vibrio harveyi</i>, the overall percent mortality of shrimp showed a gradually decreasing trend with the increase of GAA supplementary but was not significantly different from each other. In conclusion, GAA can improve the growth, antioxidant ability, and nonspecific immunity for <i>L. vannamei</i>.