Yeast cell wall (YCW), typically derived from Saccharomyces cerevisiae, contains bioactive components such as β-glucans, mannan oligosaccharides (MOS), and protein–polysaccharide complexes. Extensive research has shown that dietary supplementation with YCW can enhance growth performance, immune activity, gut health, and resistance to environmental stress in fish and shrimp. This article summarizes the mechanisms, key data, and practical recommendations for applying YCW in aquaculture.

1. Functional Components of YCW

1. β-Glucans

      β-glucans are well-known immunomodulators. They activate nonspecific immune pathways in fish and shrimp by binding to receptors on macrophages and granulocytes, enhancing phagocytosis, respiratory burst, and lysozyme activity. This leads to improved defense against bacteria, fungi, and viruses.

2. Mannan Oligosaccharides (MOS)

      MOS competes with pathogenic bacteria for binding sites in the intestinal mucosa, preventing colonization. At the same time, MOS promotes the proliferation of beneficial gut microbiota, improving nutrient absorption and gut morphology.

3. Other Components

      Minor proteins, minerals, and polysaccharides contribute to gut epithelial repair, digestive efficiency, and overall health.

2. Mechanisms of Action

1. Immune Activation
         β-glucans bind to immune receptors, stimulating phagocytosis, complement activity, and antimicrobial defenses.

2. Pathogen Blocking & Microbiota Balance
         MOS binds mannose-specific lectins on pathogenic bacteria, effectively “trapping” them and reducing adhesion to the intestinal wall.

3. Gut Integrity & Antioxidation
         YCW enhances villi height, tight-junction integrity, and upregulates antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT), protecting animals from ammonia, nitrite, pesticides, and transport stress.

3. Research Evidence and Representative Data

1. Growth and Feed Efficiency

• Multiple studies on carp, tilapia, trout, shrimp, and crustaceans show that YCW supplementation improves specific growth rate (SGR) and feed conversion ratio (FCR) when added at appropriate levels.

• In Pacific white shrimp (Litopenaeus vannamei), one feeding trial estimated an optimal YCW level of approximately 4.83 g/kg feed (≈0.483%), resulting in higher growth and immune parameters compared with the control.

2. Effective β-Glucan Levels

• Across species, effective β-glucan doses generally range from 0.05% to 0.20% of the diet.

• A coral trout study found that 0.10% β-glucan provided the best improvement in growth, antioxidant capacity, and immune enzyme activity. Excessive dosing may reduce benefits.

3. Immunity and Disease Resistance

• YCW-fed fish and shrimp typically show increased lysozyme activity, respiratory burst, complement activation, and phagocytic index.

• Disease-challenge trials frequently report higher survival rates against Vibrio, Aeromonas, and other common pathogens.

4. Gut Health and Stress Resistance

• YCW increases villi height, goblet cell density, and digestive enzyme activity.

• Enhanced antioxidant enzyme activity contributes to better tolerance to salinity shifts, ammonia spikes, and handling stress.

4. Practical Benefits in Aquaculture

1. Reduced Disease Outbreaks & Lower Dependence on Antibiotics

      By improving innate immunity and gut stability, YCW helps prevent common bacterial infections, supporting the global trend toward antibiotic reduction.

2. Improved Growth and Feed Conversion

      Better gut absorption and immune efficiency lead to improved biomass gain and more efficient use of feed — a direct economic benefit.

3. Enhanced Gut Microbiome Stability

      MOS-driven microbial modulation supports stronger digestion, better nutrient uptake, and improved resilience to environmental fluctuations.

4. Greater Antioxidant and Stress-Tolerance Capacity

      Upregulated antioxidant systems reduce cellular damage during transport, grading, crowding, or sudden parameter changes.

5. Usage Recommendations

1. Suggested Inclusion Levels

• Fish: β-glucans at 0.05%–0.20% (0.5–2 g/kg).

• Shrimp/Crustaceans: Total YCW at 0.2%–0.6% (2–6 g/kg).

  • Optimal level observed in some studies: ~4.8 g/kg for L. vannamei.

2. Avoid Over-Supplementation

      High doses do not always produce better outcomes and may overstimulate the immune system or reduce growth efficiency. Dose-response trials are recommended.

3. Consider Feed Processing and Stability

      Pelleting or extrusion temperature may affect YCW component integrity. Use products with verified β-glucan/MOS concentrations and stability data.

4. Conduct Farm-Level Trials

Start with a small-scale 8–12-week feeding trial to evaluate:

• Growth (SGR, final weight)

• Feed conversion (FCR)

• Immune markers (lysozyme, phagocytosis)

• Survival under normal and stressful conditions

• Economic return vs. additive cost

6. Conclusion

      Yeast cell wall is a valuable functional additive for aquaculture. Driven by its β-glucans and MOS, YCW enhances innate immunity, improves gut morphology, strengthens antioxidant capacity, and supports better growth and survival. When applied at species-appropriate levels, it offers both biological and economic benefits, helping the industry transition toward healthier and more sustainable production systems.