Cage aquaculture is like a series of “underwater factories,” continuously producing aquatic products—but it has also quietly become a source of nutrient input into water bodies. While high-density aquaculture boosts fishery yields, it also poses serious environmental challenges—namely, eutrophication.

 

What exactly is hidden behind this issue?

What kind of ecological mechanisms are at play? And how should we respond to this scientifically?

Invisible pollution sources: leftover feed and feces

During aquaculture, only a portion of the feed supplied is effectively absorbed and utilized by the fish; the remainder—including uneaten leftover feed and fish excrement—enters the water body in the form of organic matter and nutrient salts such as nitrogen and phosphorus. These components are precisely the “food” most critical for algae growth.

The massive influx of exogenous nutrients rapidly disrupts the original nutrient balance in lakes and reservoirs, stimulating a dramatic proliferation of algae—especially cyanobacteria—and triggering algal blooms. These blooms cause a sharp decline in water transparency and intensify fluctuations in dissolved oxygen levels, further exacerbating hypoxia at the bottom layer and pushing the ecosystem toward imbalance.

 

The Triple Threat of Eutrophication

1. External inputs continue to increase, while internal releases are intensifying.

The continuous input of leftover feed and feces keeps nitrogen and phosphorus concentrations in the water body persistently high. Under hypoxic conditions, bound phosphorus in sediments can be converted into soluble phosphorus, which is then released back into the water, creating "internal pollution." Even if feeding is stopped, this portion of phosphorus can still sustain algal growth, trapping eutrophication in a vicious cycle.

2. Dissolved Oxygen Imbalance: The Oxygen Consumption Chain from Respiration to Decomposition

Oxygen consumption in aquatic bodies primarily stems from two sources:

Direct oxygen consumption: Aquaculture fish consume large amounts of dissolved oxygen through respiration.

Indirect oxygen consumption: When residual feed, feces, and other organic matter are decomposed by microorganisms, oxygen consumption is further intensified.

Under still-water or stratified conditions, the waters beneath and around net cages—especially the bottom layer—are highly prone to oxygen depletion or even anaerobic conditions.

3. Collapse of Ecosystem Structure and Function

In eutrophic and hypoxic environments, aquatic insects, benthic organisms, and wild fish that are sensitive to pollution gradually die off or disappear, leading to a homogenization of community structure. Meanwhile, the reduced light penetration caused by algal blooms results in widespread decline of submerged aquatic plants. As these aquatic plants vanish, their crucial functions—such as stabilizing the sediment, absorbing nutrient salts, and providing habitat—also cease to exist, significantly diminishing the ecosystem’s capacity for self-regulation.

Moreover, residues of chemical substances such as antibiotics and disinfectants used in aquaculture can persist in water bodies and sediments, potentially inducing the emergence of resistance genes and amplifying them through the food chain, thereby threatening both the entire aquatic ecosystem and human health.

Precise Oxygen Replenishment: Breaking the Impasse at Its Root

After completing the foundational work—including environmental carrying capacity assessment, feed optimization, and monitoring and early warning—how can we implement efficient and precise interventions to address the environmental problems that have already occurred, especially the core challenge of oxygen depletion at the bottom layer of deep-water lakes and reservoirs?

Traditional surface aeration often has limited effectiveness; as bubbles rise, they quickly dissipate, making it difficult for them to reach the oxygen-depleted zone at the bottom. To achieve fundamental treatment, we must adopt technological approaches that directly address the root cause of the problem.

The ultra-nano-aerosol reoxygenation technology is a groundbreaking solution specifically designed to address oxygen depletion at the bottom layer of deep-water lakes and reservoirs, as well as internal pollution. By generating oxygen-rich water at supersaturated concentrations, this system achieves targeted, efficient, and long-lasting reoxygenation of oxygen-depleted bottom zones.

 

Detailed Explanation of the Technical Principle:

Precise oxygen delivery: By using dedicated pipelines, oxygen-rich water is directly delivered to the hypoxic zones at the bottom of lakes and reservoirs (such as below the thermocline and at the sediment-water interface), enabling precise targeting and avoiding wasteful oxygen loss during transport.

High-efficiency dissolved oxygen: The bubbles produced are extremely small in diameter, have a large specific surface area, and remain in the water for a significantly longer duration. As a result, their oxygen dissolution efficiency is far superior to that of conventional aeration methods.

Inhibit endogenous release: By maintaining the oxidized state at the sediment-water interface, we can effectively inhibit the release of phosphorus from sediments, thereby cutting off the key nutrient source that fuels algal growth at its very origin.

Ecological restoration synergy: Quickly increase dissolved oxygen levels at the bottom layer, improve the habitat for benthic organisms, prevent stress responses in cultured fish caused by oxygen deficiency, and promote the gradual recovery of the ecosystem.

Intelligent Management: Building a New Paradigm for Sustainable Aquaculture

Integrating automated water quality monitoring, precise oxygenation, and feed delivery into a unified “monitoring-management-control” smart management platform is an inevitable path toward achieving green development in lake and reservoir aquaculture.

 

By continuously monitoring key indicators such as dissolved oxygen, pH, and chlorophyll a in real time, the system can automatically activate oxygenation equipment and adjust feeding strategies, thereby establishing a closed-loop management system. The platform not only visually displays the improvements in water quality but also quantitatively assesses, through comparisons with historical data, the actual benefits of measures like oxygenation in inhibiting algal blooms and enhancing fish growth and feed conversion rates, providing a scientific basis for decision-making.

Conclusion

Through a comprehensive, four-pronged approach—“assessing the spatial layout based on environmental carrying capacity, controlling pollution at its source through efficient feed management, using real-time monitoring as our eyes and ears, and leveraging precise oxygenation as our key tool”—we are poised to completely break the vicious cycle of “aquaculture pollution—environmental degradation—damaged aquaculture.”

As a key breakthrough for addressing hypoxia at the bottom layer and internal pollution, ultra-nano aerosol reoxygenation technology is driving the transformation and upgrading of lake and reservoir fisheries—from an extensive, resource-intensive model toward a modern, eco-friendly, resource-conserving, and intelligently controllable ecological fishery model. In the future, only precise regulation and scientific management within the bounds of ecological carrying capacity will enable a win-win outcome for both water resource protection and fisheries development.