In modern aquaculture, the intensification of cultivation systems has led to a surge in productivity demands, which frequently results in highly contaminated systems. Among the most critical challenges to the success of Pacific white shrimp (Litopenaeus vannamei) farms is the accumulation of nitrogenous and sulfur compounds, specifically ammonia, nitrite, and sulfide.
These components are not merely byproducts of shrimp metabolism and organic matter decomposition; they act as severe stressors that can compromise the economic viability of an aquaculture project. A new integrated study, conducted by researchers from the Ocean University of China, the Sanya Oceanographic Institution, and the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), evaluated how these three factors simultaneously affect the histopathology, immune system, and genetic profile (transcriptome) of the species, revealing which of them represents the greatest threat. The findings were published in the journal Developmental and Comparative Immunology.
Key Conclusions of the Study
- Hierarchy of Damage: Nitrite demonstrated the most severe impact on the shrimp, followed by ammonia, while sulfide had the lowest relative impact under the concentrations evaluated.
- Most Vulnerable Organs: The hepatopancreas and midgut are the tissues most affected by acute stress, whereas muscle tissue exhibits the greatest resilience.
- Immunological Response: All stressors activate the antioxidant system, increasing the activity of the enzyme Superoxide Dismutase (SOD), but they deplete the Total Antioxidant Capacity (T-AOC).
- Genetic Impact: 1,400 Differentially Expressed Genes (DEGs) were identified under these stresses, affecting vital processes such as lipid metabolism, cell division, and the inflammatory response.
- Compromised Growth: Environmental stress inhibits the expression of key genes for development and molting, which explains the growth anomalies observed in ponds with poor water quality.
The Invisible Danger: Ammonia, Nitrite, and Sulfide
Ammonia nitrogen is a crucial metric in water management. It exists primarily in two forms: ionic (NH4+) and non-ionic (NH3), the latter being the most toxic due to its ability to penetrate cellular membranes. Prolonged exposure increases molting frequency and causes significant structural damage to the gills.
On the other hand, nitrite accumulates due to the decomposition of feed remains and excreta, especially when a lack of oxygen or the absence of nitrifying bacteria prevents its conversion to nitrate. Finally, sulfide, produced under anaerobic conditions at the water-sediment interface, alters organic matter synthesis and the animal’s basal metabolism.
Tissue Impact: What Happens Inside the Shrimp?
Histopathological analysis after 48 hours of exposure revealed profound damage across four fundamental tissues:
The Hepatopancreas: The Metabolic Hub
Under normal conditions, hepatopancreas cells are well-organized, and their tubules show a clear, star-shaped lumen. However, upon exposure to ammonia, cells underwent massive lysis and vacuolation. Under nitrite stress, severe necrosis and an anomalous presence of hemocytes within the interstitial spaces were observed. Finally, sulfide caused significant cellular shrinkage and the coalescence of vacuoles, thereby impairing digestive function.
The Midgut: The Defensive Barrier
The study confirmed that the intestine is highly susceptible. Under the stress of all three factors, epithelial cells detached from the basement membrane and showed fragmented or clumped nuclei, compromising nutrient absorption and defense against pathogens.
The Gills: The Respiratory System
The gills are the organ in direct contact with the environment. Nitrite and sulfide caused the greatest disorganization of the gill filaments, which shrank and distorted, affecting the shrimp’s ability to regulate its body balance and breathe adequately.
The Muscle: The Final Product
Although it was the least affected tissue, a slight fragmentation of muscle fibers and the disappearance of transverse striations were observed under nitrite stress. This suggests that, even if the shrimp survives, meat quality may be compromised by lipid oxidation processes and protein decomposition.
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Immunological and Enzymatic System Responses
The shrimp attempts to defend itself against stress through its antioxidant enzyme system. Superoxide Dismutase (SOD) activity increased significantly in the ammonia and nitrite groups, acting as the first line of defense to eliminate Reactive Oxygen Species (ROS).
Nevertheless, this defense comes at a cost. Total Antioxidant Capacity (T-AOC) decreased across all groups, indicating that environmental stress ultimately overcomes the organism’s natural defenses, leaving the shrimp vulnerable to secondary infections by pathogens such as Vibrio.
A relevant finding is that nitrite and ammonia elevated the activity of Alkaline Phosphatase (AKP), a key enzyme in aquatic immune protection, while sulfide tended to inhibit it, suggesting different mechanisms of toxicity and adaptation.
Transcriptomic Revelations: Genes Under Pressure
Using RNA sequencing, researchers identified how these stressors “turn off” or “turn on” certain genes:
- Apoptosis: The CASP9 gene, related to programmed cell death, was activated under nitrite and sulfide, confirming the tissue damage observed in microscopic sections.
- Weakened Metabolism: Ammonia reduced the expression of genes such as MTARC1, weakening the hepatopancreas’s ability to process metabolites and reduce nitrite in time.
- Inhibited Growth: The EcR (Ecdysteroid Receptor) and Hr4 genes, essential for molting and maturation, were reduced under the pressure of nitrite and ammonia. This explains why, in poor water quality conditions, shrimp not only die, but survivors exhibit notably slow growth.
General Conclusion of the Study
This comprehensive research demonstrates that water quality management is the cornerstone of health in shrimp farming. Nitrite stands as the most dangerous stressor due to its profound interference with protein metabolism and cellular integrity. The results suggest that frequent monitoring and the implementation of strategies to enhance shrimp resilience—such as the use of immune boosters—are essential to mitigate these effects.
Contact
Mengqiang Wang
MOE Key Laboratory of Marine Genetics and Breeding, Ocean University of China
Qingdao, 266003, China.
Email: wangmengqiang@ouc.edu.cn
Reference
Han, L., Yang, J., Yan, P., & Wang, M. (2025). An integrated investigation of major environmental stressors on the Pacific white shrimp Litopenaeus vannamei. Developmental & Comparative Immunology, 166, 105361. https://doi.org/10.1016/j.dci.2025.105361
Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.
