The high stocking densities used in Pacific white shrimp (Litopenaeus vannamei) aquaculture often lead to increased stress, disease susceptibility, and reduced growth performance.
A study conducted by a researcher from Purdue University Fort Wayne investigated the potential of dietary supplementation with lauric acid (LA) and N-acetyl-L-cysteine (NAC) to improve the immune and antioxidant responses of Pacific white shrimp raised under high stocking density conditions.
Challenges in intensive shrimp farming: hypoxia and oxidative stress
Intensive shrimp farming often leads to hypoxia, a condition that compromises immune function and increases disease susceptibility.
Hypoxia triggers the overproduction of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), superoxide anion (O₂•⁻), and hydroxyl radicals (•OH). These ROS cause lipid peroxidation of polyunsaturated fatty acids (PUFAs), generating harmful byproducts such as malondialdehyde (MDA).
To counteract this, organisms rely on antioxidant defense systems, including enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, as well as non-enzymatic molecules like glutathione.
The role of feed additives in shrimp aquaculture
To address hypoxia and oxidative stress challenges, the aquaculture industry has turned to feed additives such as amino acids, minerals, probiotics, prebiotics, peptides, organic acids, and nucleotides. These additives enhance innate and adaptive immunity, improve pathogen resistance, and mitigate oxidative stress. Among these, lauric acid (LA) and N-acetyl-L-cysteine (NAC) have emerged as promising candidates due to their antimicrobial and antioxidant properties.
Lauric acid: A natural immunomodulator
Lauric acid, a medium-chain fatty acid abundant in coconut oil, palm oil, and black soldier fly larvae oil, has demonstrated significant antibacterial and antiviral properties. It is particularly effective against Gram-positive bacteria, inhibiting biofilm formation, membrane biosynthesis, and virulence factors.
N-Acetyl-L-Cysteine: A powerful antioxidant
NAC, a synthetic precursor of intracellular cysteine and glutathione, is a potent antioxidant. It directly scavenges free radicals and increases cellular glutathione levels, reducing oxidative stress markers such as malondialdehyde (MDA).
Study design and methodology
The study involved 270 shrimp with an initial average weight of 0.65 grams, divided into five treatment groups. Shrimp were cultured at two stocking densities: low stocking density (LSD) with 10 shrimp per 0.80 ft³ and high stocking density (HSD) with 20 shrimp per 0.80 ft³. The five treatment groups were as follows:
- T1: Negative control in LSD (no supplementation)
- T2: Positive control in HSD (no supplementation)
- T3: HSD with 0.2% LA supplementation
- T4: HSD with 0.2% NAC supplementation
- T5: HSD with a combination of 0.2% LA and 0.2% NAC
Each treatment was replicated three times, and the experiment lasted eight weeks. Growth performance, immune response, and antioxidant activity were evaluated using various biochemical and molecular parameters.
Key findings
Improved growth performance
Shrimp fed diets supplemented with LA and NAC (T3, T4, and T5) showed better growth compared to control groups. Higher glucose and total protein levels were observed in these groups, indicating enhanced metabolic activity and nutrient utilization.
Enhanced immune response
Total hemocyte count (THC) and phagocytic index, critical indicators of immune function, were significantly higher in shrimp receiving LA and NAC supplementation. Additionally, the expression of prophenoloxidase and lysozyme, key components of the shrimp innate immune system, was elevated in T3, T4, and T5. These findings suggest that both LA and NAC can strengthen shrimp defense mechanisms against pathogens.
Increased antioxidant capacity
The study revealed that LA and NAC supplementation led to higher expression of antioxidant enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPx). At the same time, lower levels of malondialdehyde (MDA), a marker of oxidative stress, were observed in T3, T4, and T5. This indicates that these nutraceuticals effectively mitigate oxidative damage in shrimp raised at high stocking densities.
Activation of the innate immune signaling pathway
The expression of Toll-like receptor 2 (TLR-2), a gene involved in the innate immune signaling pathway, was significantly higher in shrimp fed LA and NAC. This further underscores the immunomodulatory effects of these supplements.
Implications for the shrimp industry
These findings have significant implications for the aquaculture industry, offering a practical strategy to mitigate the adverse effects of high stocking densities, ultimately leading to healthier shrimp and more sustainable farming practices.
In this regard, the study’s results could impact the shrimp farming industry in the following ways:
Reducing antibiotic dependence
The study suggests that NAC and LA supplementation could reduce the need for antibiotics in shrimp production. Strengthening the shrimp immune system makes them more resistant to diseases, potentially decreasing antibiotic usage—addressing a major issue in aquaculture.
Potential for intensive aquaculture
The study’s findings indicate that NAC and LA supplementation could be an effective strategy to improve production in intensive shrimp farming systems. Intensive shrimp farming systems are more vulnerable to health issues, stress, and diseases. These compounds could help enhance the resilience of Pacific white shrimp against oxidative stress and pathogens.
Potential use as feed additives
The study identified NAC and LA as promising candidates for feed additives in intensive shrimp aquaculture at a commercial scale. The positive results in growth, antioxidant response, and immune function support their potential use at the industry level.
Conclusion
The study demonstrates that dietary supplementation with 0.2% lauric acid (LA) and N-acetyl-L-cysteine (NAC) can significantly enhance the immune and antioxidant responses of Pacific white shrimp cultured under high stocking density conditions. By improving the expression of key antioxidant enzymes and immune-related genes, these nutraceuticals help shrimp combat oxidative stress and pathogens more effectively.
These findings position LA and NAC as promising candidates for enhancing shrimp resilience and productivity in intensive aquaculture systems.
Contact
Shafaq Fatima
Department of Biological Sciences, Purdue University Fort Wayne
Fort Wayne, Indiana, United States of America
Email: shaff01@pfw.edu
Reference (open access)
Fatima S (2025) N-acetyl-L-cysteine and lauric acid; effective antioxidant and antimicrobial feed additives for juvenile Pacific white shrimp (Litopenaeus vannamei) cultured at high stocking density. PLoS ONE 20(1): e0315819. https://doi.org/10.1371/journal.pone.0315819
