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Glycerin as a New Ingredient for Aquaculture Species Diets

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By Milthon Lujan

The increase in biodiesel production has led to a surplus of glycerol, a three-carbon sugar alcohol. This cost-effective and readily available byproduct has sparked interest among aquaculture researchers: could it be a viable dietary ingredient for fish?

An international team of scientists from the University of Coimbra (Portugal), University School Vasco da Gama (Portugal), Université de Pau et des Pays de l’Adour (France), and The New Zealand Institute for Plant and Food Research published a scientific review on the use of glycerol, also known as glycerin, in fish feed and its potential as a dietary ingredient for the feeds used in the aquaculture industry.

Glycerol: A Potential Game Changer for Aquaculture?

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There are different grades of glycerin, and crude glycerol from biodiesel contains impurities such as methanol and fatty acids. Refining removes these impurities but adds costs. The purity of the glycerin used in animal feed can significantly affect its efficacy.

The potential of glycerol as a food ingredient has been explored in various types of livestock, including pigs, cows, poultry, and even fish. While results vary, some studies suggest that glycerin can improve nutrient absorption and even act as a direct energy source. Research has reported the use of glycerol as an energy source or to replace corn in diets for tilapia, and in shrimp feed to improve growth.

On the other hand, fish farmers are constantly seeking cost-effective ways to provide their finned friends with the energy and nutrients they need. Glycerol offers a compelling alternative. Studies suggest it can be incorporated into fish diets, potentially acting as a source of:

  • Energy: Fish can easily convert glycerin into usable energy.
  • Metabolic intermediates: It can contribute essential elements for various biological processes.
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The Intriguing Effects of Glycerin on Fish Metabolism

The scientific review focuses on the use of glycerol in fish food, excluding studies on fish larvae. Researchers are examining how fish incorporate glycerin into their bodies, its impact on growth, and its effect on waste products. Understanding how different fish species (carnivores and omnivores) utilize glycerin is also a key area of research.

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Here’s what we know so far:

  • Metabolic Changes: Glycerol supplementation appears to influence how fish use energy, potentially affecting processes such as gluconeogenesis (sugar production) and lipogenesis (fat synthesis).
  • Reduced Protein Catabolism: Studies suggest that glycerol could help conserve proteins within the fish’s body, which could minimize nitrogen excretion and its environmental impact. However, further research is needed to fully understand its impact on overall protein retention.
Digestion and Metabolism of Glycerol in the Liver, Muscles, and Adipose Tissue. Source: Coelho et al., (2024); Reviews in Aquaculture
Digestion and Metabolism of Glycerol in the Liver, Muscles, and Adipose Tissue. Source: Coelho et al., (2024); Reviews in Aquaculture

The need for species-specific research

Interestingly, research suggests that carnivorous fish may not metabolize glycerol as efficiently as omnivorous species. This highlights the need for further research on the effects of glycerol on:

  • Fish with different feeding habits: How do herbivores, omnivores, and detritivores respond to glycerol supplementation?
  • Developmental stages: Does the impact of glycerol differ in larvae, juveniles, and adult fish?
  • Environmental factors: How do salinity and temperature influence glycerol utilization?

The future of glycerol in aquaculture feeds

To fully unlock the potential of glycerol in sustainable aquaculture practices, further research is required. Here are some key areas for further exploration:

  • Impact on different fish species: It is essential to understand how fish with different feeding habits (carnivores, omnivores, herbivores) utilize glycerol.
  • Developmental stages: Researching the effects of glycerol on fish at different life stages (larvae, juveniles, adults) can provide valuable insights.
  • Environmental factors: Studying the influence of factors such as salinity and temperature on glycerol metabolism in fish is crucial for optimizing its use in aquaculture systems.
  • Impact of impurities and optimization of glycerol inclusion: Understanding the role of potential impurities in commercially available glycerol and how to better incorporate it into fish feed formulations is important for maximizing its benefits.
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Conclusion

The study’s findings can be summarized as follows:

  • Species matter: Fish respond differently to glycerol supplementation. Nile tilapia, an omnivore, has been the most studied, but results for carnivorous fish are limited.
  • Dose and purity count: The quantity and quality of glycerol used can significantly affect its efficacy. Costs associated with purifying lower-quality glycerol may be a barrier.
  • Metabolic changes: Glycerol can be used for energy or converted into fatty acids. Long-term studies are needed to see if these changes are temporary or permanent.
  • More research is needed: Studies on diverse fish species, under different environmental conditions, are crucial. The impact of glycerol on different tissues (liver, fat, muscle) also needs further investigation.
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While glycerol shows promise for sustainable fish feeding, much remains to be learned. Future research should address these complexities to unlock its full potential for aquaculture.

The study was funded by the Fundação para a Ciência e Tecnologia (FCT; Portugal), co-financed by the European Regional Development Fund (ERDF/FEDER) through the Operational Programme for Competitiveness and Internationalisation (POCI/POFC); and funds from the R&D Unit Center for Functional Ecology—Science for People and the Planet (CFE). Open access has been funded by New Zealand Institute for Plant and Food Research Ltd.

Contact
Leonardo J. Magnoni
Plant and Food Research Centre, The New Zealand Institute for Plant and Food Research Limited
293 Akersten St. Nelson 7010, New Zealand.
Email: leonardo.magnoni@plantandfood.co.nz

Reference (open access)
Coelho, M., Palma, M., Tavares, L. C., Panserat, S., Viegas, I., & Magnoni, L. J. Glycerol supplementation in farmed fish species: A review from zootechnical performance to metabolic utilisation. Reviews in Aquaculture. https://doi.org/10.1111/raq.12930