Ozone in Aquaculture: Is It Safe for Black Porgy?
"Balancing water quality and fish health in recirculating systems."
Marine finfish aquaculture in South Korea increasingly relies on recirculating aquaculture systems (RAS) to ensure stable production. RAS offers better control over environmental conditions, extending the optimal culture period and reducing the impact of external factors like temperature fluctuations and coastal contamination. However, the success of RAS hinges on effective water treatment, and ozone is emerging as a key tool.
Ozone's strong oxidation properties make it attractive for controlling pathogens, reducing solids, and improving overall water quality in aquaculture. But, while ozone can enhance water quality, it can also produce harmful byproducts known as total residual oxidants (TRO). The challenge lies in finding the right ozone dose that maximizes benefits without harming the fish.
This article breaks down a study on how different ozone doses affect black porgy (Acanthopagrus schlegeli) in RAS. The goal is to understand the impact of ozone on fish health, growth, and overall well-being, providing insights into safer and more sustainable aquaculture practices.
A Cautious Safety Question
Ozone is being considered in aquaculture because it can improve water quality, but its safety depends on how it is applied and controlled. For black porgy, the relevant concern is the balance between treatment benefits and possible exposure to residual ozone. Available evidence should therefore be interpreted cautiously rather than as proof that ozone is universally safe or unsafe.
Controlled Ozonation
Ozonation in recirculating aquaculture systems involves applying different ozone dosages while evaluating ozone demand, ozone kinetics, and changes in water quality, including fluorescent organic matter. In seawater, ozone oxidizes ammonia through a bromide-catalyzed reaction, with nitrogen gas reported as the end product and almost complete ammonia-nitrogen removal possible in the cited study. However, ozone can be toxic to aquatic organisms, residual ozone may harm watercourses, and the gas is unstable, difficult and dangerous to store, so it is generally generated on-site and used immediately.
From Ancient Aquaculture to Ozone
Aquaculture developed independently several millennia ago in multiple regions, driven by demand for seafood as well as ornamental and religious motives. The Food and Agriculture Organization identifies the Tang Dynasty as particularly significant, when China’s Li family name coincided with the common name of widely cultivated common carp. More recent histories describe a progression from ancient ponds and medieval practices to science-based aquaculture, while ozone has gained a growing role in aquaculture applications.
The Ozone Balancing Act: Benefits vs. Risks
The study evaluated black porgy in RAS with varying ozone doses: no ozone (control), 20 g ozone/kg feed/day, and 40 g ozone/kg feed/day. The 44-day trial monitored the fish for behavioral changes, growth, blood parameters, and histological alterations in their gills and livers. This comprehensive approach provides a detailed picture of ozone's effects.
- Behavior and Mortality: No significant behavioral changes or mortalities were observed in the ozonated systems.
- Growth and Blood: The ozone treatments didn't affect growth or blood parameters.
- Histological Changes: Both ozone treatments caused histological changes in the gills and livers, with more pronounced cellular damage at the higher dose.
Evidence Remains Developing
Recent research continues to examine how ozone affects water quality and aquatic organisms in recirculating systems. The available evidence suggests that ozone may offer treatment benefits, but its biological effects require careful evaluation. For black porgy specifically, conclusions should remain cautious unless studies directly test that species under comparable aquaculture conditions.
Where Ozone Systems Fail
Practical use of ozone in aquaculture is limited by its low stability, poor solubility, and potentially harmful effects on aquatic organisms. Implementation mistakes can create avoidable water-quality and safety problems, which is why farms need more than a focus on ozone output alone. When selecting an ozone generator, important dimensions include output range, feed-gas requirements, control method, materials compatibility, and safety architecture.
Benefits Versus Exposure Risk
Ozone may provide useful water-treatment functions, but comparisons with other approaches should account for both performance and biological risk. Its potential value is not separable from the need to control exposure, residual oxidants, and system-specific ozone demand. For black porgy production, the most defensible comparison is therefore one that weighs water-quality goals against species safety and operational complexity.
Optimizing Ozone Use in Aquaculture: Future Directions
The study underscores the need for careful ozone management in aquaculture. While ozone offers benefits like pathogen control and improved water quality, it's crucial to minimize potential harm to fish. Histological changes in the gills and livers of black porgy indicate that even seemingly safe ozone doses can have adverse effects.
Treatment Requires Control
The cited research presents ozone as a potentially effective tool for oxidative sterilization and water-quality improvement in recirculating aquaculture systems, including systems used for Litopenaeus vannamei. It also emphasizes that safe and robust treatment requires defining the ozone demand and ozone kinetics of the specific system. Findings from zebrafish research reinforce the trade-off: ozone improved certain water-quality parameters and altered hematological profiles, but also caused adverse gill effects.
Species-Specific Validation
Future work should clarify how ozone exposure affects different cultured species and life stages. Research that measures both water-quality benefits and biological responses would help distinguish useful treatment from harmful exposure. For black porgy, species-specific testing would be needed before broad safety conclusions are justified.
System-Level Constraints
Ozone safety is part of a larger aquaculture-system challenge rather than a single-equipment question. Effective use depends on matching treatment intensity to water conditions, maintaining reliable controls, and preventing harmful residual exposure. These requirements can make ozone more demanding to operate than a simple disinfection step.
From Research to Farms
Ozone is used in aquaculture and water treatment to improve water quality and reduce pathogens during pretreatment and treatment processes. Commercial and research-scale installations have been reported across hatcheries, research institutions, and integrated aquaculture operators in Singapore, Saudi Arabia, Australia, and India. These examples show practical interest in the technology, but they do not by themselves establish that ozone is safe for black porgy.
To safely harness ozone's benefits in seawater RAS, future studies should focus on:
<ul><li><b>Long-term effects of TRO:</b> Evaluating the cumulative impact of total residual oxidants on fish health over extended periods.</li><li><b>Optimal ozone doses for different species and life stages:</b> Determining the specific ozone requirements for various aquaculture species and their developmental stages.</li><li><b>Mitigation strategies:</b> Exploring methods to reduce TRO formation or minimize their toxicity in RAS.</li></ul>