Scientists studied how different types of food affect the brains of baby rainbow trout, especially their appetite control. They compared fish fed a traditional diet with fish oil and fishmeal to those fed a plant-based diet. The research tracked changes in brain chemicals that control hunger over 100 days. While the plant-based diet didn’t immediately change these brain chemicals, it did create subtle differences that might explain why some fish eat less and grow slower on plant-based food. This research helps fish farmers understand how to create better plant-based fish food that keeps fish healthy and growing well.

The Quick Take

  • What they studied: How different types of fish food (traditional fish-based versus plant-based) affect the brain chemicals that control hunger and appetite in baby rainbow trout as they grow.
  • Who participated: Baby rainbow trout from first feeding through 100 days of growth, divided into groups eating either traditional fish-based food or plant-based food.
  • Key finding: Plant-based diets created slightly different patterns in brain chemicals that control appetite, which may explain why some fish eat less and grow slower on this type of food, even though the initial changes weren’t dramatic.
  • What it means for you: If you work in fish farming or care about sustainable seafood, this research suggests that plant-based fish food needs better design to keep fish eating normally and growing well. The findings may eventually help create healthier plant-based options for farmed fish.

The Research Details

Researchers raised baby rainbow trout from their first meal and divided them into two groups: one eating traditional food made with fish oil and fishmeal, and another eating plant-based food with no fish ingredients. They tracked changes in the fish’s brain over 100 days by measuring specific brain chemicals (called genes and mRNA) that control hunger and appetite.

The scientists focused on measuring brain chemicals that either increase or decrease appetite, similar to how your brain controls whether you feel hungry or full. They also measured other brain chemicals involved in how the body uses energy and responds to food.

This approach allowed them to see exactly when and how the different diets affected the fish’s brain development and appetite control systems from the very beginning of life.

Understanding how food affects a fish’s brain from the earliest stages is crucial for fish farming. If scientists can figure out why plant-based diets sometimes make fish eat less and grow slower, they can design better plant-based fish food. This matters because fish farming is increasingly moving toward plant-based ingredients to be more sustainable and reduce pressure on wild fish populations.

This is a controlled experimental study that tracked changes over time, which is a solid research approach. The researchers measured specific biological markers in the brain, which is more precise than just observing behavior. However, the study focused specifically on rainbow trout, so results may not apply to all fish species. The exact number of fish studied wasn’t specified in the available information, which would be helpful for understanding how reliable the findings are.

What the Results Show

The plant-based diet did not immediately cause major changes in the brain chemicals that control appetite when fish first started eating. This was somewhat surprising because it suggested the fish’s brains adapted initially to the new food.

However, as the fish grew over the 100-day period, the plant-based diet created different patterns in how brain chemicals changed compared to fish eating traditional food. Some appetite-increasing chemicals (like neuropeptide Y) gradually increased more in plant-fed fish, while appetite-decreasing chemicals showed different patterns.

The researchers also found that other brain chemicals involved in energy use and metabolism responded differently depending on which diet the fish ate. These differences became more noticeable as the fish got older, suggesting the effects of diet on the brain build up over time.

These subtle brain chemistry differences may explain why fish on plant-based diets sometimes eat less food and don’t grow as quickly, even though their brains don’t show dramatic immediate changes.

The study revealed that multiple brain systems work together to control appetite and energy use. When fish ate plant-based food, several of these systems responded differently, not just one single brain chemical. This suggests that plant-based diets affect the fish’s brain in complex ways that involve multiple pathways. The researchers also noted that the timing of these changes was important—some brain chemicals changed early while others changed gradually over weeks and months.

Previous research suggested that plant-based diets might cause immediate and obvious problems with appetite control in fish. This study shows the situation is more nuanced—the brain doesn’t immediately reject plant-based food, but subtle changes accumulate over time. This finding helps explain why some fish farms have had mixed results with plant-based feeds and suggests that the problems develop gradually rather than appearing right away.

The study only looked at rainbow trout, so we don’t know if these findings apply to other fish species used in farming. The researchers measured brain chemicals but didn’t directly measure how much the fish actually ate or how fast they grew, though they suggest these measurements would likely show differences. The study also didn’t test different types of plant-based diets to see if some plant-based formulas work better than others. Finally, while the researchers tracked changes over 100 days, we don’t know what happens to these fish long-term after that period.

The Bottom Line

For fish farmers: Plant-based fish food can be used, but it may need to be reformulated to better match how fish brains respond to nutrition. The current plant-based options appear to create subtle changes that reduce feeding and growth. Moderate confidence in this recommendation based on this single study. For consumers: This research supports continued development of sustainable plant-based fish farming, but current plant-based feeds may not yet be optimal. More research is needed before making major changes to farming practices.

Fish farmers and aquaculture companies should care most about this research, as it directly affects how they feed farmed fish. Environmental advocates interested in sustainable seafood should also pay attention, as it shows both the promise and current limitations of plant-based fish food. Scientists studying fish nutrition and brain development will find this research valuable. Regular consumers of farmed fish don’t need to change their behavior based on this single study, but may benefit from future improvements in plant-based fish farming.

The changes in brain chemistry happened gradually over the 100-day study period, with some differences appearing within the first few weeks and others developing more slowly. If fish farmers were to change their feed formulas based on this research, improvements in fish growth and feeding would likely take several weeks to months to become noticeable. Long-term effects beyond 100 days are unknown.

Want to Apply This Research?

  • If you’re involved in fish farming, track weekly measurements of feed consumption and fish growth rates when switching between traditional and plant-based diets. Record the specific plant-based formula used and note any changes in fish behavior or appetite over 8-12 week periods.
  • For aquaculture professionals: Document your current plant-based feed formulas and their results, then work with nutritionists to adjust ingredient ratios based on this research. Consider adding supplements that might better match how fish brains respond to plant-based ingredients.
  • Establish a baseline of fish growth and feeding behavior on your current diet, then monitor these metrics weekly if you switch to plant-based options. Track changes over at least 12 weeks to see if the subtle brain chemistry changes described in this research translate to measurable differences in your fish farm’s performance.

This research describes laboratory findings in fish and should not be interpreted as direct health advice for humans. The study examined brain chemistry in rainbow trout and may not apply to other fish species or to human nutrition. While this research is scientifically sound, it represents one study and should be considered alongside other research before making major changes to fish farming practices. Anyone involved in aquaculture should consult with fish nutrition specialists and veterinarians before changing feed formulas. This information is for educational purposes and does not replace professional nutritional or veterinary guidance.