The natural antioxidant chrysin helps rainbow trout cope with stress caused by overcrowding

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By Milthon Lujan

crisina trucha

Intensive aquaculture, while boosting aquatic production, also exposes fish to a significant stressor: overcrowding. This can lead to delayed growth, weakened immune systems, and even diseases. Finding safe and affordable ways to mitigate these effects is crucial for sustainable fish farming.

But what if there were a natural ingredient that could help rainbow trout thrive in these stressful conditions?

A published study presents the results of research conducted by a team of scientists from RUDN University, the University of Hormozgan, Urmia University, and East China Normal University, studying the potential of chrysin as a dietary supplement for rainbow trout under overcrowding stress. Researchers tested different levels of chrysin in the fish’s diet and monitored their growth, immune response, and stress resistance.


Chrysin is a compound of plant origin found in sources such as passionflower, propolis, and even fungi. Its superpower? A diverse arsenal of benefits, from boosting immunity and fighting inflammation to acting as an antioxidant and antimicrobial agent. But what about fish?

Research suggests it has a multitude of health benefits, and a new study delves into its potential as a superfood for trout.

Feeding Trout with Chrysin

For fish farm owners, the primary goal is to increase production intensity. Due to this, fish are often kept in overcrowded tanks. These unnatural conditions hurt fish health: chronic and acute stress occurs, harming growth and immunity.

In this regard, aquaculturists are looking for harmless supplements or medications that can help cope with these negative consequences. Researchers focus on natural medicines derived from plants.

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The researchers took a group of rainbow trout and divided them into different dietary groups. Some received normal fish feed, while others received feed with varying doses of chrysin (from 100 mg/kg to 700 mg/kg). After 56 days, the fish were put to the test: a 14-day simulation of overcrowding stress.

Before and after the experiment, researchers measured the immunological parameters of the fish’s blood and also compared the growth rates of fish from different groups.

Amazing Results

“The increase in production has caused fish to be stressed by overcrowding. Chronic and acute stress reduces fish growth and immunity. Therefore, it is important to seek safe and cost-effective strategies that can help mitigate the harmful effects of stress. Several studies have confirmed the beneficial effects of immunostimulants in fish. Natural ingredients are the most well-known feed additives to combat stress in aquatic animals. They receive special attention due to their numerous positive properties, so the search for more effective compounds continues,” said Morteza Yousefi, associate professor at the RUDN Department of Veterinary Medicine.

Trout fed with chrysin outperformed their counterparts that did not consume chrysin in several key areas:

  • Growth: Those following a chrysin diet of 300 mg/kg to 700 mg/kg gained more weight and grew faster.
  • Immunity: Their natural defenses received a boost, with increased activity of antioxidant enzymes and immune response markers. Chrysin helps neutralize harmful free radicals that can damage cells and activates the fish’s natural defense system to fight infections.
  • Stress resilience: They coped better with overcrowding stress and showed fewer negative impacts on their physiology and health. Chrysin helps regulate cortisol levels, the stress hormone that can wreak havoc on fish health.
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Increased red blood cell count and other blood parameters, promoting better oxygen supply and overall health.

Application in Rainbow Trout Farming

The findings suggest that chrysin could change the game for trout farming. Adding it to their diet could lead to:

  • Increased aquaculture performance: Better growth means more fish to harvest.
  • Reduced risk of diseases: A stronger immune system helps fish fight infections and stay healthy.
  • Better fish welfare: Less stress means happier and healthier fish.


“Chrysin at 300-500 mg/kg of the diet in rainbow trout improves growth, immunity, and stress resistance in fish under overcrowding stress. In the future, the effect of chrysin on fish resistance to stress caused by transportation can be studied. Additionally, further research is proposed to evaluate the mechanism of action of chrysin at the molecular level, as well as its protective effect on fish exposed to infections,” concluded Yousefi.

Of course, more research is needed to fine-tune the optimal chrysin dose and explore its long-term effects. But this study paints a promising picture for a future where this natural hero helps rainbow trout thrive, even in overcrowded conditions.

Mehdi Naderi Farsani
Department of Fisheries, Faculty of Natural Resources, Urmia University, Urmia, Iran
Email: me.nf1987@yahoo.com

Reference (open access)
Yousefi, M., Nedaei, S., Farsani, M. N., Ghafarifarsani, H., Zhang, M. L., & Du, Z. Y. (2023). Dietary chrysin supplementation improves growth performance, immune responses, antioxidant status, and resistance against crowding stress in rainbow trout. Aquaculture Reports, 32, 101708.

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