Nutritional Modulation of Growth, Immune, and Metabolic Gene Expression in Penaeus vannamei Through Glucogenic Amino Acids and Folic Acid: Functional Additives and Physiological Regulation

Intensified shrimp farming has driven interest in functional feed additives that support growth and immune competence in Penaeus vannamei. This study evaluated whether glycine (Gly), glutamine (Gln), and aspartic acid (Asp), combined with folic acid (FA), act as functional additives in this species. A first trial (14 days, initial weight 5.0 ± 0.3 g, n = 8 per treatment) screened 15 diets at two amino acid concentrations (2.5 and 25 mg/g) with FA held constant at 2 µg/g. A second trial (5 weeks, initial weight 8.894 ± 0.12 g, n = 30 per treatment across three replicate tanks) tested three selected treatments (Gly 2.5, Asp 2.5, and Gly+Asp 2.5 mg/g) for growth and immune responses after a challenge with Vibrio parahaemolyticus AHPND (LD50 = 1.1 × 105 CFU/mL). Low doses (2.5 mg/g) of Gly, Asp, and their combination upregulated growth-related genes, including atpe, igf1, tor, pi3k, and akt (p < 0.05), whereas high doses (25 mg/g) produced no change or downregulation, consistent with a biphasic dose–response. Growth performance did not differ significantly among treatments: final weights were 13.95 ± 0.58 g (control), 13.41 ± 0.46 g (Gly), 12.83 ± 1.15 g (Asp), and 13.29 ± 0.62 g (Gly+Asp) (p > 0.05). The specific growth rate (SGR) ranged from 1.04 to 1.28%/day across treatments. Survival during the 5-week trial was 76.67% (control), 93.33% (Gly), 70.00% (Asp), and 73.33% (Gly+Asp), with no significant differences among treatments (p > 0.05). Mortality was not specific to the Gly+Asp group; the Asp group showed the highest mortality (30.00%). Surviving animals from the Gly+Asp group showed a stronger immune response after bacterial challenge, with a 24.30-fold increase in gill mnk at 12 h post-infection, but this observation is limited to survivors. Early expression of atpe, igf1, and tor explained 74% of the variation in final weight. These results are preliminary and should be interpreted with caution. Moderate doses of glycine and aspartic acid, combined with folic acid, modulated a pro-growth transcriptional program, but this did not translate into improved growth performance under the conditions tested. The cause of mortality remains unknown and was not specific to the combined treatment. The safety of these additives at the tested doses is not established. Further studies with additional doses, protein-level analyses, water quality monitoring, and histopathological evaluation are required before any practical application can be recommended.