Researchers tested whether adding a plant called Tagetes erecta (also known as marigold) to fish food could make farmed fish look more colorful and appealing to buyers. They fed one group of large yellow croaker fish regular food, and gave three other groups the same food plus different plant extracts. After four weeks, the fish that ate food with Tagetes erecta had noticeably more red and yellow coloring in their skin compared to the other groups. The scientists think this happens because the plant helps the fish’s bodies absorb and use natural color-producing substances better. This discovery could help fish farmers grow more beautiful fish that customers want to buy.

The Quick Take

  • What they studied: Can adding a marigold plant extract to fish food make the fish more colorful and golden-looking?
  • Who participated: Large yellow croaker fish (a type of fish commonly raised on farms for food). The exact number of fish wasn’t specified in the study summary.
  • Key finding: Fish fed food with Tagetes erecta extract became significantly more red and yellow colored compared to fish eating regular food. The red coloring was 1.25 times stronger, and the yellow coloring was noticeably higher (statistically significant at p = 0.028).
  • What it means for you: If you eat farmed fish, this research suggests farmers may soon be able to grow more colorful, visually appealing fish by using natural plant supplements in their feed. This could improve the appearance of fish at the market without using artificial dyes. However, this research is specific to one fish species and hasn’t been tested on humans yet.

The Research Details

Scientists created four different fish diets to test. One was a basic diet with no additions (the control group), and three others had the same basic diet plus one of three different plant extracts added. The three plant extracts tested were: Tagetes erecta (marigold) at 200 mg per kilogram of food, astaxanthin (a natural red pigment) at 200 mg per kilogram, and amaranth leaf extract at 200 mg per kilogram. The fish were fed these different diets for 28 days (about 4 weeks), and then researchers measured how much the fish’s color had changed.

The researchers specifically measured color using a scientific scale that separates color into different components: one scale measures how red or green something is (called the a* value), and another measures how yellow or blue something is (called the b* value). They took these measurements from different parts of the fish’s body, including the belly area.

Beyond just measuring color, the scientists also did early investigations into how the plant extract actually works. They looked at whether the Tagetes erecta extract helped the fish’s bodies absorb carotenoids (natural substances that create red and yellow colors) better, and whether it affected melanogenesis (the process of making dark pigments in skin).

This research approach is important because it tests a practical solution to a real problem in fish farming. When fish are raised in crowded conditions, they often lose their natural colors, which makes them less attractive to customers and reduces their market value. By testing natural plant supplements instead of artificial dyes, this study offers a way to improve fish appearance while potentially keeping the product more natural. The study also goes beyond just measuring results—it tries to understand the mechanism (how it actually works), which helps scientists know whether this approach might work for other fish species too.

The study was published in a peer-reviewed journal called Aquaculture Nutrition, which means other experts reviewed it before publication. However, some important details are missing from the abstract provided: the exact number of fish used in the study isn’t specified, and we don’t know if the experiment was repeated multiple times or how many fish were in each group. The study lasted only 4 weeks, which is relatively short-term. The research appears to be preliminary, especially the mechanistic studies (the investigation into how it works), which the authors themselves describe as ‘initial.’ This means more research would be needed to fully understand the process and confirm these results.

What the Results Show

The main finding was that Tagetes erecta extract was more effective at improving fish color than the other two plant supplements tested (astaxanthin and amaranth leaf extract). Specifically, the fish that received Tagetes erecta in their food showed a red-green color value (a* value) that was 1.25 times higher than the fish eating regular food with no supplement. This means the fish became noticeably more red-colored.

The study also found that the yellow-blue color value (b* value) on the fish’s belly was significantly higher in the Tagetes erecta group compared to the control group. The researchers reported this difference was statistically significant (p = 0.028), which means it’s unlikely to have happened by chance alone.

These color improvements happened after just 28 days of feeding the fish the supplemented food. This relatively quick result suggests that the plant extract works fairly rapidly to change fish coloration.

The early mechanistic research suggested that Tagetes erecta works by helping the fish’s bodies better absorb and use carotenoids (the natural pigments that create red and yellow colors) and by affecting how the fish produce melanin (dark pigments in skin). However, the researchers noted these were initial studies, meaning more detailed research would be needed to fully understand exactly how the process works.

While the abstract doesn’t provide detailed secondary findings, it’s notable that astaxanthin and amaranth leaf extract were also tested but were less effective than Tagetes erecta at improving color. This suggests that not all plant supplements work equally well for this purpose, and that Tagetes erecta may have unique properties that make it particularly good at enhancing fish color. The fact that the researchers tested multiple supplements shows they were trying to find the best option rather than just testing one product.

The study addresses a known problem in fish farming: fish raised in crowded conditions with suboptimal breeding conditions often lose their natural coloring and flesh quality. This is a recognized issue in the aquaculture industry that affects the commercial value of farmed fish. The research builds on the general knowledge that diet affects fish coloration, but appears to be novel in specifically testing Tagetes erecta for this purpose in large yellow croaker. The use of natural plant extracts rather than synthetic dyes aligns with growing interest in natural approaches to aquaculture.

Several important limitations should be considered: First, the exact number of fish used in the study isn’t specified in the abstract, making it difficult to assess whether the sample size was large enough to draw reliable conclusions. Second, the study only lasted 4 weeks, so we don’t know if the color improvements would continue, stay the same, or fade over longer periods. Third, the mechanistic studies (investigating how the plant extract actually works) are described as ‘initial,’ meaning they’re preliminary and would need more detailed follow-up research. Fourth, this study was only done on one species of fish (large yellow croaker), so we don’t know if the same results would occur in other fish species. Fifth, the study doesn’t appear to measure whether the color improvements affect the nutritional quality of the fish or whether consumers actually prefer the more colorful fish. Finally, there’s no information about potential costs, safety concerns, or whether the color improvements are permanent or fade over time.

The Bottom Line

Based on this research, fish farmers may want to consider testing Tagetes erecta extract as a dietary supplement for large yellow croaker to improve color appearance (moderate confidence level—more research is needed). The supplement appears safe to use since it’s a natural plant extract, but farmers should start with small-scale testing before using it widely. The evidence is strongest for short-term color improvement (4 weeks), so long-term effects remain unclear. Consumers should be aware this is an emerging technique and more research is needed to confirm long-term safety and effectiveness.

Fish farmers raising large yellow croaker for commercial sale should be most interested in this research, as it directly addresses their goal of producing more attractive fish. Consumers who buy farmed fish might care about this research if they prefer naturally-colored fish without artificial dyes. Aquaculture researchers and nutritionists should pay attention as it may lead to similar research in other fish species. People with allergies to marigold plants should be aware if this supplement becomes commonly used in farmed fish. However, this research is NOT relevant to people eating wild-caught fish, as it only applies to farmed fish.

Based on this study, color improvements appeared within 4 weeks of feeding the supplement. However, we don’t know how long these improvements last after the supplement is stopped, or whether they continue to improve beyond 4 weeks. Realistic expectations would be to see noticeable color changes within 2-4 weeks if this supplement is used, but longer-term studies would be needed to understand the full timeline of effects.

Want to Apply This Research?

  • If you’re a fish farmer using this supplement, track the color values (a and b values) of your fish weekly using a color measurement device, or take standardized photos of fish under consistent lighting conditions every 7 days to visually monitor color progression.**
  • Fish farmers could implement a practical change by adding Tagetes erecta extract at 200 mg per kilogram of feed to their current feeding program and monitoring results over 4 weeks to see if color improvements match the research findings.
  • Establish a baseline color measurement before starting the supplement, then measure color weekly for at least 8 weeks to track both the improvement phase and whether color changes plateau or fade. Keep records of feeding amounts, water conditions, and fish health to identify any other factors affecting results.

This research is specific to large yellow croaker fish and has not been tested on humans. The study was conducted over only 4 weeks, so long-term safety and effectiveness are unknown. Fish farmers should consult with aquaculture specialists before implementing dietary changes. Consumers should note that while this supplement appears to be natural, regulatory approval and safety testing may vary by country. This research does not provide medical advice for human consumption and should not be used to make health claims about eating fish treated with this supplement. Always consult with qualified professionals before making significant changes to fish farming practices or dietary choices.