Scientists tested whether adding a natural substance called fulvic acid to fish food could help large yellow croakers survive in hot water during summer. They fed different groups of young fish food with varying amounts of this supplement over two months and tracked their growth, health, and gut bacteria. Fish that received the right amount of fulvic acid grew bigger, survived better, and had healthier digestive systems compared to fish without the supplement. This discovery could help fish farmers protect their crops as oceans get warmer due to climate change, without needing to use antibiotics.

The Quick Take

  • What they studied: Whether adding fulvic acid (a natural substance) to fish food helps young croakers grow better and stay healthy when water gets too hot
  • Who participated: Young large yellow croaker fish divided into five groups, studied from mid-July through mid-September during the hottest part of summer
  • Key finding: Fish fed food with 0.8% fulvic acid showed the best growth and survival rates, with noticeably better weight gain compared to fish without the supplement
  • What it means for you: If you work in fish farming, this suggests a natural, non-antibiotic way to protect fish during heat waves. However, this research was done on one specific fish species in controlled conditions, so results may differ in real-world farms or with other fish types

The Research Details

Researchers took young large yellow croaker fish and divided them into five groups. Each group received the same food, but with different amounts of fulvic acid mixed in—from none at all up to 16 grams per kilogram of food. They kept the fish in these conditions for exactly two months during summer when water temperatures were naturally high. The scientists then examined what happened inside the fish’s bodies by looking at three different levels: genes (which control how cells work), the chemicals produced during metabolism (how the body uses food for energy), and the bacteria living in the fish’s gut (which help with digestion and health).

They focused their detailed analysis on two important parts: the liver (which processes nutrients and handles stress) and the gut (which digests food and fights off harmful bacteria). By examining these areas at multiple biological levels, the researchers could understand not just whether the fish grew better, but also exactly how the fulvic acid was helping them survive the heat.

This research approach is important because it doesn’t just measure whether fish got bigger—it shows the actual biological mechanisms (the ‘how’ and ‘why’) behind the improvement. By looking at genes, metabolism, and gut bacteria together, scientists can understand if fulvic acid is truly helping fish handle heat stress or if something else is going on. This multi-level approach gives much stronger evidence than just weighing the fish at the end.

The study was conducted over a full two-month period during actual summer heat conditions, which makes the results more realistic than laboratory experiments. The researchers used multiple scientific methods to analyze the data, which strengthens their conclusions. However, the paper doesn’t specify exactly how many fish were used in each group, which makes it harder to judge how reliable the results are. The study focused on only one fish species, so we don’t know yet if these results would work for other types of fish.

What the Results Show

Fish that received fulvic acid in their food grew significantly better than fish without it. The best results appeared when the food contained 0.8% fulvic acid (which equals 8 grams per kilogram). These fish gained more weight and grew faster than the control group with no supplement.

When scientists looked inside the fish’s bodies, they found that fulvic acid activated important biological pathways—essentially turning on the fish’s natural defense systems against heat stress. Two key pathways were particularly active: one that helps the body break down and use fats for energy, and another that controls how the body manages fats and sugar. Both of these are especially important when fish are stressed by high temperatures.

The supplement also changed the fish’s gut bacteria in a beneficial way. Specifically, it increased the amount of a type of bacteria called Actinobacteriota, which is known to reduce inflammation and keep the digestive system healthy. A healthier gut means better digestion, better nutrient absorption, and a stronger immune system.

Beyond growth and survival, the fish that received fulvic acid showed improved overall health markers. The changes in their gut bacteria suggest that the supplement wasn’t just helping them survive the heat—it was actually improving their digestive health and immune function. This is important because a healthy immune system helps fish fight off infections and diseases, which is especially critical when they’re already stressed by high temperatures.

This research builds on earlier studies showing that fulvic acid can help various organisms handle stress. However, this appears to be one of the first detailed studies examining exactly how fulvic acid works in fish at the genetic and bacterial levels. Previous research suggested fulvic acid might help, but this study provides much stronger evidence by showing the specific biological mechanisms involved.

The study only tested one species of fish (large yellow croaker), so we don’t know if these results apply to other fish species used in aquaculture. The exact number of fish used in each group wasn’t reported, which makes it harder to judge how confident we should be in the results. The experiment was conducted in controlled conditions during summer, so real-world results on actual fish farms might be different. We also don’t know how long the benefits last after fish stop receiving the supplement, or whether the supplement works equally well in different types of water or with different feeding schedules.

The Bottom Line

If you manage a fish farm raising large yellow croakers, adding 0.8% fulvic acid to fish food appears to be a promising way to help them survive hot water and grow better (moderate confidence based on this single study). This is particularly useful as an alternative to antibiotics. However, you should start with a small test batch before switching all your fish food, since results may vary depending on your specific farm conditions. Consult with an aquaculture specialist before making major changes to your feeding program.

Fish farmers raising large yellow croakers in warm climates or during hot seasons should pay attention to this research. Climate scientists and environmental managers concerned about aquaculture sustainability may also find this relevant. This research is less directly applicable to people raising other fish species, though some benefits might transfer. Home aquarium owners with croakers could potentially benefit, though the supplement may be difficult to obtain for small-scale use.

Based on this two-month study, you could expect to see noticeable improvements in fish growth within 4-8 weeks of starting the supplement. However, the full benefits to immune function and gut health might take the entire 8-week period to develop. Long-term effects beyond two months are unknown.

Want to Apply This Research?

  • If using this supplement on a farm, track weekly weight measurements of sample fish from each feeding group, recording the average weight gain per week. Also monitor survival rate (percentage of fish alive) and note any visible health changes like fin condition or activity level.
  • For aquaculture users: Switch to fulvic acid-supplemented feed at 0.8% concentration during hot months, and maintain detailed feeding logs noting the date, amount fed, and batch number of supplement used. For aquarium hobbyists: If fulvic acid supplements become available for home use, add them according to product instructions and monitor fish growth and behavior weekly.
  • Establish a baseline by measuring your fish population’s growth rate and survival for 2-4 weeks before adding the supplement. Then introduce fulvic acid and continue measuring the same metrics weekly for at least 8 weeks. Compare the ‘before’ and ‘after’ periods to see if you notice the improvements described in this study. Keep records of water temperature, feeding amounts, and any other changes to help explain your results.

This research describes results from a controlled scientific study on one fish species and should not be considered medical or veterinary advice. Before making changes to fish feeding programs or aquaculture practices, consult with a veterinarian, aquaculture specialist, or fish health professional. Results may vary significantly based on local conditions, water quality, fish genetics, and other factors not controlled in this study. Fulvic acid supplements should be sourced from reputable suppliers and used according to product guidelines. This summary is for informational purposes and does not constitute professional advice for your specific situation.