Scientists fed rainbow trout different types of mushroom stem meals to see how it affected their gut bacteria. They tested three types of mushrooms—button mushrooms, shiitake, and oyster—mixed into fish food for six weeks. The mushroom stems didn’t harm the fish’s intestines but did change which bacteria lived in different parts of their digestive system. Some mushroom types helped beneficial bacteria grow, while others had different effects. This research suggests mushroom stems could be a sustainable, healthy food ingredient for farmed fish that supports their gut health naturally.

The Quick Take

  • What they studied: Whether feeding fish mushroom stem meals would change the types and amounts of bacteria living in their digestive systems, and whether this would be good or bad for the fish.
  • Who participated: Young rainbow trout weighing about 120 grams each, divided into groups that ate different diets for 42 days (about 6 weeks). The fish were kept in controlled tank conditions.
  • Key finding: Different mushroom types caused different changes in gut bacteria depending on where in the fish’s digestive system you looked. Button mushroom stems increased helpful bacteria like Mycoplasma and Weissella, while oyster mushroom stems increased Paenibacillus bacteria. The fish’s intestines stayed healthy throughout.
  • What it means for you: If you raise fish for food, mushroom stems could be a sustainable, affordable ingredient that keeps fish healthier by improving their gut bacteria. This may reduce the need for antibiotics and other treatments. However, this research is only in fish—we don’t yet know if it applies to other animals or humans.

The Research Details

Researchers divided young rainbow trout into four groups. One group ate normal fish food (the control group), while three other groups ate fish food mixed with 30% mushroom stem meals from three different types of mushrooms: button mushrooms (Agaricus bisporus), shiitake mushrooms (Lentinula edodes), and oyster mushrooms (Pleurotus ostreatus). All fish ate their assigned diet for 42 days in identical tank conditions.

At the end of the study, scientists collected samples from three different sections of each fish’s intestines: the pyloric caeca (a pouch-like area near the stomach), the anterior intestine (front section), and the posterior intestine (back section). They analyzed the bacteria in each section using DNA sequencing, which identifies which bacteria species are present and how many of each type there are.

The researchers also examined the intestinal tissue under a microscope to make sure the mushroom diets didn’t damage the fish’s digestive system.

This research design is important because it shows that different parts of a fish’s digestive system have different bacteria communities, and different foods affect these communities in different ways. By looking at three separate intestinal regions, the scientists could understand how mushroom stems work throughout the entire digestive system. This detailed approach helps explain why mushroom stems might be beneficial—they’re not just changing bacteria randomly, but in specific, organized ways that support digestion.

This study was published in Scientific Reports, a well-respected peer-reviewed journal, which means other scientists reviewed the work before publication. The researchers used modern DNA sequencing technology to identify bacteria accurately. The study had a clear control group for comparison and kept all conditions identical except for the diet. However, the study only looked at one type of fish and didn’t test the long-term effects beyond 42 days. The exact number of fish per group wasn’t specified in the abstract, which makes it harder to judge the study’s statistical power.

What the Results Show

The mushroom stem diets changed the bacteria communities in the fish’s intestines, but the changes were different depending on which mushroom type was used and which part of the intestine was examined. In the pyloric caeca and front intestine, fish fed button mushroom stems showed increased amounts of potentially helpful bacteria called Mycoplasma and Weissella. The front intestine also showed a unique increase in Legionella bacteria only in fish eating button mushroom stems.

Fish fed oyster mushroom stems showed an increase in Paenibacillus bacteria in the pyloric caeca. Shiitake mushroom stems didn’t cause major changes in specific bacteria types, but they did reduce the overall diversity of bacteria in some intestinal sections.

All three mushroom diets reduced the amount of Desulfobacterota bacteria that was very common in the control group. This is potentially beneficial because high levels of this bacteria type aren’t necessarily helpful for fish health.

Importantly, none of the mushroom diets damaged the intestinal lining or caused any visible harm to the fish’s digestive system.

The research revealed that different intestinal regions responded differently to the mushroom diets. The front intestine appeared to be where new bacteria from the mushroom diet temporarily settled and colonized. The back intestine was more stable and resistant to change, mainly hosting bacteria involved in breaking down carbohydrates. The pyloric caeca showed the most dramatic shifts, suggesting this region is where the mushroom ingredients have their strongest effect on digestion and nutrient absorption. These region-specific patterns suggest that mushroom stems work as ‘prebiotics’—ingredients that feed beneficial bacteria and help them grow.

This research builds on previous studies showing that what fish eat directly affects their gut bacteria. Earlier research in other fish species and in mammals has shown that plant-based ingredients can shift gut bacteria communities. This study is novel because it specifically tests mushroom stems (a waste product from mushroom farming) as a sustainable ingredient and shows that different mushroom types have different effects. The finding that mushroom stems act as prebiotics aligns with human nutrition research showing that mushrooms contain compounds that feed beneficial bacteria.

The study only tested one fish species (rainbow trout), so we don’t know if the same effects would occur in other fish species or other animals. The study lasted only 42 days, so we don’t know what happens with longer-term feeding. The abstract doesn’t specify how many fish were in each group, making it unclear how confident we should be in the results. The study didn’t measure whether these bacteria changes actually improved the fish’s growth, health, or disease resistance—it only showed that the bacteria changed. We also don’t know if the effects would be the same at different mushroom meal percentages or in different water temperatures.

The Bottom Line

For fish farmers: Mushroom stem meals, particularly from button mushrooms, appear to be a promising sustainable ingredient that can be added to fish feed at 30% levels without harming fish health and while potentially improving their gut bacteria. Confidence level: Moderate—this is promising but needs more research on actual health benefits. For consumers: This research doesn’t directly affect you unless you raise fish, but it suggests that using food waste (mushroom stems) to improve farmed fish health is possible, which could eventually mean healthier, more sustainably-raised fish in stores.

Fish farmers and aquaculture companies should pay attention to this research as a potential way to improve fish health and reduce costs using a sustainable ingredient. Feed manufacturers might consider developing mushroom stem-based products. Consumers interested in sustainable food production should find this encouraging. This research does NOT yet apply to humans eating mushrooms or fish—it’s specifically about using mushroom stems as fish feed.

In the study, bacteria changes were visible after 42 days (6 weeks) of feeding. If a fish farmer started using mushroom stem meals, they might expect to see shifts in their fish’s gut bacteria within 4-6 weeks. However, we don’t know how long it takes to see actual health improvements like better growth or disease resistance.

Want to Apply This Research?

  • If you’re a fish farmer using this research, track weekly feed consumption rates and monthly fish weight gain to see if mushroom stem meals improve growth efficiency compared to your previous feed.
  • Start by replacing 30% of your current fish feed with mushroom stem meal from a reliable supplier. Monitor your fish for any signs of stress or illness during the first two weeks. Keep detailed records of which mushroom type you’re using (button, shiitake, or oyster) and any changes you notice in fish behavior or health.
  • Establish a baseline of your current fish health metrics (growth rate, feed conversion ratio, disease incidents) before switching feeds. After introducing mushroom stem meals, continue measuring these same metrics monthly for at least 3-6 months to determine if there are real improvements. Consider having water quality and fish health checked regularly by a veterinarian.

This research is specific to rainbow trout and laboratory conditions. Results may not apply to other fish species, wild fish, or different farming environments. This study shows changes in bacteria but does not prove that these changes improve fish health, growth, or disease resistance. Before making changes to fish feed or farming practices, consult with an aquaculture specialist or fish veterinarian. This research does not apply to human nutrition or health. Always follow local regulations regarding fish feed ingredients and farming practices.