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Challenges and Solutions for Phosphorus Management in Freshwater Aquaculture

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By Milthon Lujan

Dietary factors affecting phosphorus waste in farmed fish. Source: Nathanailides (2023), Fishes.
Dietary factors affecting phosphorus waste in farmed fish. Source: Nathanailides (2023), Fishes.

With the increasing demand for seafood products, aquaculture offers a promising solution to meet these needs. However, as the aquaculture industry expands, it brings along significant environmental challenges. Among them, aquaculture-induced eutrophication stands out as one of the primary concerns.

In an article published by scientists from the University of Ioannina, the University Research Center of Ioannina (URCI), and the Hellenic Ministry of Rural Development and Food, the importance of understanding the mechanisms affecting phosphorus retention and absorption in farmed fish is highlighted.

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Understanding these mechanisms is essential for fish farmers to develop strategies to reduce phosphorus pollution from open flow fish farms and improve the sustainability of aquaculture.

The Environmental Challenge

Legislation and environmental interests are increasingly focused on safeguarding both marine and freshwater ecosystems from the harmful impact of aquaculture. While numerous measures are in place to protect these ecosystems, aquaculture-induced eutrophication remains a significant issue.

The culprits behind this problem are water-soluble phosphorus, uneaten feed, feces, and metabolic waste from fish farms, all of which contribute to elevated phosphorus concentrations in adjacent waters.

Open Flow Fish Farms

In open outdoor freshwater fish farms, the problem can be even more immediate, as the excess phosphorus is introduced directly into ecosystems, disrupting the delicate balance of aquatic life.

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The overabundance of phosphorus can lead to harmful algal blooms, oxygen depletion, and the deterioration of water quality.

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Addressing this problem requires a comprehensive understanding of the mechanisms that affect nutrient retention and absorption in farmed fish.

The Role of Nutrient Uptake

Several key factors come into play when it comes to phosphorus retention in the diet of farmed fish. Intestinal enzymes, transporters, and regulatory factors play fundamental roles.

For example, alkaline phosphatase and various transporters aid in the absorption of phosphorus in the anterior intestine. The pH, calcium levels, and vitamin D in the fish’s system also influence these enzymes and transporters. Additionally, intestinal morphology and the gut microbiome can affect this crucial process.

Sustainable Solutions

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To reduce phosphorus pollution from open flow fish farms and make aquaculture more sustainable, the study suggests adopting a multi-pronged approach:

  • Optimize Feed Composition: Adjusting the composition of fish feed can significantly impact phosphorus release. Developing feeds that maximize nutrient utilization and minimize phosphorus waste is key.
  • Functional Feed Ingredients: Incorporating functional feed ingredients that enhance nutrient absorption and reduce waste can play a crucial role in sustainable aquaculture practices.
  • Gut Health Management: Ensuring the health of the fish’s gut is fundamental. This can be achieved through proper nutrition and disease management, which can enhance nutrient retention.
  • Bioremediation and Absorbing Materials: Treating effluent aquaculture waters with bioremediation techniques and absorbing materials can remove phosphorus from the water, preventing it from entering the environment.
  • Mitigating Anti-Nutritional Factors: Processing methods and the use of functional feed additives can help mitigate the presence of anti-nutritional factors in fish diets, which can lead to better nutrient utilization.

The Path Forward

By addressing these challenges, the aquaculture industry can significantly reduce its environmental impact, safeguard the health of aquatic ecosystems, and contribute to global food security.

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Sustainable phosphorus management, through scientific research and innovative solutions, is a fundamental step towards ensuring the long-term viability of aquaculture. As the world continues to rely on aquaculture to meet its seafood needs, the industry’s commitment to sustainability and environmental responsibility is paramount.

Conclusion

“The data reviewed in the study indicate that the phosphorus retention efficiency of different species of farmed fish may vary due to factors such as their physiological characteristics, feeding habits, and digestive physiology. Phosphorus requirements and absorption mechanisms may differ among fish species, and some species exhibit specialized adaptations in their intestines,” conclude the researchers.

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They also report the existence of various methods and strategies that can contribute to reducing phosphorus pollution from fish farms and that the knowledge of phosphorus absorption mechanisms, dietary factors, anti-nutritional substances, and intestinal morphology can be optimized to reduce phosphorus release.

Reference (open access)
Nathanailides, C.; Kolygas, M.; Tsoumani, M.; Gouva, E.; Mavraganis, T.; Karayanni, H. Addressing Phosphorus Waste in Open Flow Freshwater Fish Farms: Challenges and Solutions. Fishes 2023, 8, 442. https://doi.org/10.3390/fishes8090442

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