Garlic, onion, and probiotics to improve the health of rainbow trout

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By Milthon Lujan

Rainbow trout. Source: Hero
Rainbow trout. Source: Hero

Traditionally in rainbow trout aquaculture, antibiotics, and chemicals have been used to combat pathogens, raising concerns about environmental contamination and antibiotic resistance.

A study by scientists from Yalova University, Akdeniz University, the Mediterranean Fisheries Research Production and Training Institute, İzmir Kâtip Çelebi University, Tokat Gaziosmanpaşa University, and Çanakkale Onsekiz Mart University explored the potential of garlic powder, onion powder, and probiotics, both individually and in combination, to enhance the performance and health of rainbow trout (Oncorhynchus mykiss).

Natural Alternatives: Garlic, Onion, and Probiotics!

Garlic, the potent protector


This allicin-rich wonder has long been praised for its antibiotic properties. In fish, studies suggest that garlic can:

  • Boost growth: Improve digestion and energy utilization, leading to increased weight gain.
  • Strengthen immunity: Stimulate the immune system to fight infections more effectively.
  • Enhance appetite: The tasty aroma of garlic can encourage fish to eat more, promoting healthy growth.

However, the effectiveness of garlic may vary based on factors such as dosage, fish species, and feeding duration. Finding the right balance is key!

Onion, the antioxidant champion

Onions contain a wealth of flavonoids and thiosulfinates, acting as natural growth and immune system stimulants. Research shows that onions can:

  • Improve digestion: Enhance the production of vitamins and enzymes, leading to better nutrient absorption.
  • Stimulate immunity: Like garlic, onions can strengthen the immune system’s defenses against diseases.
  • Offer antioxidant benefits: The high quercetin content of onions provides valuable protection against cellular damage.
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While initial studies on onions in fish feeds are promising, more research is needed to fully unlock their potential.

Probiotics, the gut guardians


Probiotics from lactic acid bacteria (LAB) are well-established heroes in aquaculture. They:

  • Improve feed utilization: Help fish digest food more efficiently, extracting the maximum nutrients.
  • Inhibit harmful bacteria: Compete and suppress pathogenic microorganisms, reducing the risk of diseases.
  • Boost growth and immunity: Enhance overall health and well-being, leading to better growth and disease resistance.

Synergy is the key

The combination of these natural powerhouses could be the greatest promise. Studies suggest that blends of garlic, onion, and probiotics may have synergistic effects, further enhancing fish health and growth.

In this regard, for eight weeks, scientists fed rainbow trout juveniles with diets containing varying levels of probiotics (P), garlic (G), and onion (O) powder. The goal? Evaluate their effects on growth, blood parameters, and overall health.

“Seven practical diets were formulated that were isonitrogenous (49% protein) and isolipidic (20% lipids), and the diets included P, O, and G at concentrations of 0.1, 1, and 1%, respectively, replacing wheat flour,” the researchers reported.

Garlic: the big winner


The results were revealing:

  • Growth boost: Rainbow trout fed a diet supplemented with 1% garlic powder exhibited significantly higher growth rates compared to fish fed probiotic diets or a combination of probiotics and onion. This suggests that garlic may offer a natural way to enhance fish growth performance.
  • Improved efficiency: Garlic also appears to enhance feed utilization. Fish fed the garlic diet had a lower feed conversion ratio (FCR), meaning they required less food to gain weight compared to those on the probiotic diet. This translates to reduced feeding costs and environmental impact.
  • Protein power: While not performing the best in protein utilization, diets with onion and the probiotic and onion mix showed higher net protein utilization (NPU) compared to other groups. This indicates that these combinations may offer benefits for protein absorption and metabolism.
  • Blood health improvement: Garlic’s influence extended beyond growth and affected fish’s blood parameters. Groups fed the garlic diet had significantly higher packed cell volume (PCV) and hemoglobin (Hb) levels compared to those on probiotic and probiotic onion diets. These indicators suggest better oxygen transport capacity and overall blood health in garlic-fed fish.
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Finally, regarding enzymatic activity, serum levels of alkaline phosphatase, indicative of bone health and metabolism, were higher in fish fed garlic and probiotic diets with garlic.


Overall, this study highlights the potential of garlic as a natural supplement to promote growth, improve feed efficiency, and enhance blood health in rainbow trout. While more research is needed to optimize the dosage and explore possible interactions with other components of the diet, garlic emerges as a promising alternative to antibiotics in sustainable aquaculture practices.

The study was funded by the Scientific and Technological Research Council of Turkey (TÜBİTAK).


Derya Güroy
Department of Aquaculture, Armutlu Vocational School, Yalova University, Armutlu, Yalova, Türkiye
Email: dguroy@yahoo.com

Reference (open access)
Güroy, D., Emre, N., Yalım, F.B. et al. Interaction of dietary garlic (Allium sativum), onion (Allium cepa), and probiotic on the growth performance and health status of juvenile rainbow trout (Oncorhynchus mykiss). Aquacult Int (2024). https://doi.org/10.1007/s10499-024-01388-5