Scientists studied how the food baby rainbow trout eat affects the genes that control how their bodies process sugar and fat. They compared fish that ate regular fish food with fish that ate plant-based food from the moment they started eating. Over 100 days, they measured changes in the fish’s liver genes. The results showed that all fish went through natural changes as they grew, but fish eating plant-based food had slower changes in some important genes related to fat handling. This suggests that plant-based diets might make it harder for young fish to develop their normal metabolism, which could explain why these fish don’t grow as well.

The Quick Take

  • What they studied: How different types of food affect the genes in a fish’s liver that control sugar and fat processing as the fish grows from birth to 100 days old
  • Who participated: Baby rainbow trout (a type of fish commonly raised on farms) that were fed either commercial fish food or plant-based food starting from their first meal
  • Key finding: Fish eating plant-based food showed slower changes in genes related to fat processing compared to fish eating regular fish food, even though both groups went through similar natural development patterns
  • What it means for you: If you eat fish or work in fish farming, this research suggests that the type of food given to young farm-raised fish matters for their health and growth. Plant-based fish food may need to be improved to help fish develop properly, though more research is needed to understand the full impact

The Research Details

Researchers raised baby rainbow trout from the moment they started eating and gave some fish regular commercial fish food while others received plant-based food. They collected samples from the fish’s livers at six different time points over 100 days and used a special lab technique called RT-qPCR to measure how active different genes were. This technique counts the amount of messenger RNA (the instructions cells use to make proteins) for genes involved in processing sugar and fat. By measuring these genes at multiple time points, the scientists could track how the fish’s metabolism naturally changed as they grew and how the different diets affected these changes.

Understanding how young fish develop their ability to process different foods is important for fish farming because it helps farmers choose better feed options. Since rainbow trout naturally eat meat in the wild, their bodies may not be well-designed to handle plant-based diets. By looking at the genes that control metabolism, scientists can see exactly where plant-based diets cause problems, which helps them develop better plant-based feeds that work with the fish’s natural biology.

This study provides detailed molecular data by measuring gene activity at multiple time points, which gives a clear picture of how metabolism develops. The researchers used established scientific methods (RT-qPCR) that are reliable for measuring gene activity. However, the paper doesn’t specify exactly how many fish were studied, which makes it harder to judge how confident we should be in the results. The findings align with previous observations that fish on plant-based diets grow more slowly, which adds credibility to the molecular findings.

What the Results Show

As baby rainbow trout grew over 100 days, their livers naturally shifted from focusing on breaking down sugar (glycolysis) to focusing on making and storing fat (lipogenesis). This is a normal part of development. Most genes involved in sugar processing decreased in activity over time, while genes involved in fat production and storage increased. This pattern happened in both groups of fish, showing that this metabolic shift is a natural part of growing up.

However, fish that ate plant-based food showed weaker versions of these changes. Their genes didn’t increase or decrease as dramatically as the fish eating regular food. This suggests that plant-based diets may interfere with the normal developmental process. The researchers noted that one gene called gck (which helps process sugar) behaved differently—it stayed relatively active throughout development in both groups, suggesting this gene is especially important for young fish.

The most notable differences appeared in genes related to fat handling, particularly genes called fasn and acly. These genes normally increase significantly as fish grow, but in fish eating plant-based food, the increase was less pronounced. This could explain why these fish don’t grow as well—their bodies may not be efficiently making and storing the fat they need for energy and growth.

The study revealed that the timing of metabolic changes is important. Different genes peaked in activity at different points during the 100-day period, suggesting that the fish’s body follows a specific developmental schedule. Fish on plant-based diets appeared to follow a similar schedule but with reduced intensity, like they were going through the same steps but not as completely. This pattern consistency suggests that plant-based diets don’t completely derail fish development but rather slow down or dampen the normal process.

Previous research had shown that rainbow trout fed plant-based diets grow more slowly and don’t gain as much weight as fish eating regular fish food. This new study provides the molecular explanation for why this happens—the genes controlling fat production and energy storage don’t activate as strongly. The findings fit well with what scientists already knew about rainbow trout being carnivorous fish that evolved to eat meat, not plants. This research adds detail to that understanding by showing exactly which genes are affected and how.

The study doesn’t clearly report how many individual fish were tested, which makes it difficult to know how reliable the results are. The researchers only looked at the liver, so we don’t know if similar changes happen in other parts of the fish’s body. The study was conducted in a lab setting with controlled conditions, so results might be different in natural environments or commercial fish farms. Additionally, the research only looked at gene activity (mRNA levels), not whether the actual proteins these genes produce were affected or how the fish’s body actually functioned. Finally, the study only examined two diet types, so we don’t know if other plant-based formulations might work better.

The Bottom Line

Based on this research, fish farmers should be cautious about switching young rainbow trout to plant-based diets without additional modifications. The evidence suggests that plant-based feeds may need to be improved to better support normal metabolic development. If plant-based feeds are used, they should be supplemented with nutrients that help activate the genes involved in fat processing. This is a moderate-confidence recommendation based on molecular evidence, though more research on actual fish growth and health outcomes would strengthen it.

Fish farmers and aquaculture companies should pay attention to these findings when developing or choosing feeds for young rainbow trout. Consumers who eat farmed rainbow trout might care about this research because it affects the quality and sustainability of their food. Nutritionists and veterinarians working with fish should be aware of these findings. People interested in sustainable food production should note this because plant-based fish feeds could reduce environmental impact if they can be improved to work better. However, this research is very specific to rainbow trout and early development, so it may not apply to other fish species or to adult fish.

Changes in gene activity happen relatively quickly—the researchers saw measurable differences within the first 100 days of feeding. However, improvements from better plant-based feed formulations would likely take several months to show up as better growth in actual fish. If farmers implement changes based on this research, they should expect to see improvements in growth rates and feed efficiency over a full growing season (typically 12-18 months for market-size rainbow trout).

Want to Apply This Research?

  • If you’re involved in fish farming, track the growth rate and feed conversion ratio (how much feed is needed to gain one pound of body weight) of young rainbow trout on different diet types weekly. Compare these measurements between fish on plant-based diets and fish on traditional diets to see if improvements in feed formulation are working.
  • For aquaculture operations: Test supplementing plant-based feeds with specific nutrients that support fat metabolism (such as omega-3 fatty acids or amino acids that activate lipogenesis genes). Track which supplements produce the best growth results. For consumers: Choose farmed rainbow trout from producers who are actively researching and improving plant-based feed options, supporting the development of more sustainable aquaculture.
  • Establish a baseline of growth metrics for fish on current feeds, then gradually introduce improved plant-based formulations while maintaining detailed records of growth, feed consumption, and health indicators over 3-6 month periods. Use these data to identify which nutritional modifications most effectively restore normal metabolic development patterns.

This research describes molecular changes in fish livers and does not directly measure health outcomes, growth rates, or food safety in farmed fish. The findings are specific to rainbow trout and early development stages and may not apply to other fish species or life stages. While the research provides useful insights for aquaculture professionals, decisions about fish feed formulation should be made in consultation with fish nutrition experts and veterinarians. This study was conducted in controlled laboratory conditions and results may differ in commercial farming environments. Consumers should not make dietary choices based solely on this research; consult healthcare providers for personalized nutrition advice.