Scientists tested whether an extract from a water plant called Hydrilla verticillata could help a type of fish called Labeo rohita grow better and resist disease. They fed different groups of fish varying amounts of this plant extract for two months, then exposed them to harmful bacteria. The fish that received the right amount of plant extract grew faster, had stronger immune systems, and survived better when exposed to the disease-causing bacteria. This suggests that natural plant extracts might be a useful way to improve fish health in farming situations.

The Quick Take

  • What they studied: Whether a natural extract from a water plant could help fish grow bigger, stay healthier, and resist bacterial infections
  • Who participated: 450 young fish (Labeo rohita fingerlings) divided into 15 groups of 30 fish each, receiving different amounts of plant extract over 60 days
  • Key finding: Fish that received 300 milligrams of plant extract per kilogram of food showed the best growth, strongest immune response, and lowest death rates when exposed to harmful bacteria, compared to fish that received no extract or too much extract
  • What it means for you: If you’re involved in fish farming, this suggests that adding this specific water plant extract to fish feed at the right dose could naturally improve fish health and reduce disease losses. However, this research is specific to one fish species and would need to be tested in real farm conditions before widespread use.

The Research Details

Researchers conducted a controlled experiment where they divided 450 young fish into 15 equal groups. Each group received fish food mixed with different amounts of Hydrilla verticillata plant extract—some got none, while others got 75, 150, 300, or 600 milligrams per kilogram of food. The fish ate this special food for 60 days while living in separate tanks. After this feeding period, all the fish were exposed to a harmful bacteria called Aeromonas hydrophila to see how well they could resist infection.

Throughout the study, researchers measured many things: how much the fish grew, how much they weighed, and how efficiently they converted food into body mass. They also took blood samples to check for signs of stress, liver health, and immune system strength. They counted how many fish survived the bacterial challenge and compared survival rates between groups.

This type of study is called a controlled experiment because researchers carefully controlled everything except the one thing they were testing—the amount of plant extract. This design helps prove that any differences between groups were caused by the plant extract, not by other factors.

This research approach is important because it tests whether a natural substance could improve fish health in practical farming situations. By measuring multiple health markers—growth, stress levels, immune function, and disease resistance—the researchers could understand exactly how the plant extract works. Testing the fish with actual disease-causing bacteria makes the results more meaningful than just measuring growth alone.

The study used a reasonable number of fish (450 total) spread across multiple groups, which helps make the results more reliable. The researchers measured many different health markers rather than just one, which gives a complete picture. However, the study was conducted in controlled laboratory tanks, not in real fish farms, so results might differ in actual farming conditions. The study was published in a peer-reviewed journal, meaning other scientists reviewed it before publication. The specific sample size for each measurement wasn’t always clearly stated in the abstract, which is a minor limitation.

What the Results Show

Fish that received 300 milligrams of plant extract per kilogram of food gained significantly more weight and converted their food into body mass more efficiently than fish receiving no extract. Interestingly, fish that received the highest dose (600 milligrams) actually grew less well than those receiving 300 milligrams, suggesting that more isn’t always better.

The plant extract appeared to protect the fish’s cells from damage. Blood tests showed that fish receiving the extract had lower levels of a harmful substance called malondialdehyde (which indicates cell damage) and higher levels of protective enzymes that fight cellular damage. This suggests the extract acts as a natural antioxidant, similar to how vitamins protect human cells.

Fish receiving the plant extract showed signs of better liver function and less stress. Their blood tests showed improved liver enzyme patterns and lower levels of cortisol (a stress hormone). Their immune systems also appeared stronger, with higher levels of infection-fighting proteins called immunoglobulins and an enzyme called lysozyme that kills bacteria.

Most importantly, when exposed to harmful bacteria, fish that received 300 milligrams of plant extract had much lower death rates compared to fish receiving no extract. This is the most practical benefit—the extract helped fish survive a serious bacterial infection.

The study found that 300 milligrams per kilogram of food was the optimal dose. At this level, all measured benefits peaked. Lower doses (75 and 150 milligrams) showed some benefits but not as much as 300 milligrams. The highest dose (600 milligrams) actually reduced some benefits, suggesting that excessive amounts of the extract might be counterproductive. Based on growth data, researchers calculated that the ideal dose was approximately 252 milligrams per kilogram of food.

This research builds on previous studies showing that natural plant extracts can improve fish health. However, most prior research focused on single health measures like growth or immune function. This study is more comprehensive because it measured growth, stress levels, liver function, antioxidant protection, immune response, and disease resistance all together. The findings align with other research suggesting that aquatic plants contain beneficial compounds, but this is one of the first studies specifically testing Hydrilla verticillata extract in this fish species.

The study was conducted in controlled laboratory conditions with tanks, not in real fish farms where conditions are more variable. Results might differ in actual farming environments. The research focused on only one fish species (Labeo rohita), so results may not apply to other fish species used in farming. The study didn’t test the extract against other potential treatments, so we don’t know if it’s better or worse than other methods of improving fish health. The exact costs of producing and using this extract weren’t discussed, so practical affordability for farmers is unknown. Finally, the study didn’t track long-term effects beyond the 60-day feeding period and disease challenge.

The Bottom Line

If you’re a fish farmer raising Labeo rohita, adding approximately 250-300 milligrams of Hydrilla verticillata extract per kilogram of fish feed appears to improve growth and disease resistance. This recommendation has moderate confidence because it comes from a well-designed controlled study, but it should be confirmed through real-world farm testing before widespread adoption. Start with smaller-scale trials before converting all your feed. Consult with aquaculture specialists in your region about sourcing and implementing this extract.

Fish farmers raising Labeo rohita (a commercially important fish species in Asia) should find this most relevant. Aquaculture researchers and feed manufacturers might also be interested in developing products based on these findings. This research is less relevant for people raising other fish species or for home aquarium hobbyists, as the benefits may not apply to different species. People interested in natural, chemical-free approaches to fish farming would find this particularly interesting.

Based on this study, you would expect to see improved growth within the 60-day feeding period. Disease resistance improvements would become apparent when fish are exposed to infection, which could happen naturally on a farm or through deliberate testing. Long-term effects beyond 60 days are unknown, so farmers should monitor fish health continuously rather than assuming benefits continue indefinitely.

Want to Apply This Research?

  • If using an aquaculture management app, track weekly weight measurements of fish fed with the plant extract versus control groups, recording the specific dose used (aim for 250-300 mg/kg of feed). Also track mortality rates and any disease outbreaks, noting the date and severity.
  • For fish farmers: Source Hydrilla verticillata extract and gradually incorporate it into your feed at the recommended dose. Start by treating 10-20% of your fish population while monitoring growth and health metrics. If results match the study findings, gradually expand to larger portions of your operation.
  • Establish a baseline by measuring current growth rates and disease incidence in your fish population. After implementing the extract at the recommended dose, measure the same metrics weekly for at least 60 days. Compare your results to the baseline and to any control groups not receiving the extract. Track feed costs and any changes in feed efficiency. Document any health improvements or problems observed.

This research is specific to Labeo rohita fish and laboratory conditions. Results may not apply to other fish species or to real-world farm environments. Before implementing dietary changes in commercial fish farming operations, consult with aquaculture veterinarians and specialists familiar with your local conditions. This extract should not replace established disease prevention practices such as water quality management and biosecurity measures. Always follow local regulations regarding feed additives and supplements. Individual results may vary based on water quality, temperature, stocking density, and other farm-specific factors.