Comparative Evaluation of Yeast-Derived Components as Immunostimulants for Modulating Growth Performance and Health Status of Pacific White Shrimp (Penaeus vannamei)

This study aimed to compare the effects of three brewer’s yeast-derived immunostimulants—an autolyzed yeast containing nucleotides (AY), a highly purified 1,3/1,6-β-glucan (PB), and a yeast cell wall product containing mannan-oligosaccharides (YCW)—on the growth performance and health status of juvenile Pacific white shrimp (Penaeus vannamei). An 8-week growth trial was conducted for shrimp (initial body weight 1.83 ± 0.01 g), fed with diets supplemented with 0.1% AY, 0.015% PB, and 0.1% YCW, respectively. Growth performance, serum biochemical parameters, tissue morphology, immune gene expression and gut microbiota were assessed, followed by a Vibrio parahaemolyticus challenge trial. The results showed that AY and YCW groups achieved growth performance comparable to the control group, while PB exhibited a numerically lower weight gain rate than the other groups (p > 0.05). Serum biochemical analysis indicated that AY and YCW significantly reduced aspartate aminotransferase activities relative to the control (p < 0.05), while dietary AY tended to elevate serum protein, albumin, globulin, triglycerides, and cholesterol levels (p > 0.05). In addition, AY optimized hepatopancreatic and intestinal morphology. Dietary PB significantly upregulated the expression of hepatopancreatic antioxidant and inflammatory genes (SOD, TGF-β1) and suppressed the intestinal abundance of Vibrio (p < 0.05). The challenge test showed a marginally higher 3-day post-challenge survival of PB (76.7%) and AY (73.3%) than that of controls (53.3%) (p < 0.1), and PB retained the highest survival on day 7. Collectively, these findings reveal the three yeast-derived ingredients are functionally distinct immunostimulants: AY (nucleotide-rich autolysate) serves as a growth-compatible and gut–heptopancreas restorative additive supporting regular grow-out periods; YCW (mannan-oliosacchaides-rich cell wall) acts as a microbiota-modulating gut barrier enhancer for long-term intestinal health; and PB (purified β-glucan) activates hepatic antioxidant and immune pathways for superior short-term disease resistance. These findings highlight that immunostimulant choice in shrimp should be matched to production phase and disease-risk context.