Scientists have discovered that fish and shellfish have trillions of microscopic organisms living in their digestive systems, similar to humans. These tiny creatures help the animals digest food, absorb nutrients, and fight off diseases. Researchers found that different types of fish and shellfish have different communities of these microorganisms, depending on where they live (freshwater or saltwater), water temperature, and what they eat. Understanding these relationships could help fish farms grow healthier animals more efficiently, reduce disease, and make seafood farming more sustainable for our planet.

The Quick Take

  • What they studied: How the invisible bacteria and microorganisms living in fish and shellfish stomachs help them digest food, get nutrients, and stay healthy
  • Who participated: This is a review article that examined hundreds of previous studies about gut bacteria in different types of fish (like salmon and trout) and shellfish (like oysters and shrimp) from both freshwater and ocean environments
  • Key finding: The bacteria living in fish and shellfish guts are essential helpers that break down food, create important nutrients the animals need, and protect them from getting sick. Different species have different types of bacteria based on their environment and diet
  • What it means for you: If you eat farmed fish or shellfish, understanding these bacteria could lead to healthier, more sustainably raised seafood. Fish farms might use special supplements or dietary changes to improve the health of the animals, which could mean better quality food for consumers

The Research Details

This is a review article, which means scientists read and analyzed hundreds of previous research studies about gut bacteria in aquatic animals. Instead of doing their own experiment, they looked at what other researchers had discovered about how bacteria help fish and shellfish digest food and stay healthy.

The researchers compared findings across different types of aquatic animals—both fish with backbones (finfish) and animals with shells (shellfish)—and looked at how bacteria differ between freshwater species (like trout) and saltwater species (like salmon). They examined how factors like water temperature, saltiness of water, and what the animals eat affect which bacteria live in their guts.

This type of study is valuable because it brings together all the scattered research into one big picture, helping scientists and fish farmers understand the complete story of how these invisible helpers work.

Understanding gut bacteria in farmed fish and shellfish is important because it could help us grow more food with fewer problems. If we can keep these animals healthier by managing their gut bacteria, we can reduce disease outbreaks, use less medicine, and grow more food in a sustainable way. This matters for feeding our growing population while protecting the environment.

This is a review article published in a respected scientific journal, which means it was checked by other experts before publication. The strength of this type of study depends on the quality of the research it reviews. Since it summarizes findings from many different studies, it gives a broad overview but doesn’t provide the strongest type of evidence on its own. The conclusions are based on what scientists have already discovered, not on brand new experiments.

What the Results Show

The research shows that gut bacteria in fish and shellfish play three major roles: they help break down complex foods that the animals couldn’t digest alone, they help the animals absorb nutrients from their food, and they create important substances the animals need to survive and stay healthy.

The bacteria living in different aquatic animals are quite different from each other. Fish that live in freshwater have different bacterial communities than fish that live in the ocean. Even within shellfish, different species have their own unique bacterial populations. These differences exist because of the environment the animals live in (temperature, saltiness, acidity of water) and what they naturally eat.

The research also shows that the bacteria in these animals’ guts are shaped by the animals’ own genetics and diet. When farmers change what they feed farmed fish, the bacteria in their guts change too. This suggests that by carefully choosing what to feed farmed animals, we might be able to improve their health and growth.

Additional findings suggest that these gut bacteria help protect fish and shellfish from getting sick by fighting off harmful bacteria and viruses. The bacteria also help the animals’ immune systems work better. Some bacteria even create vitamins and other essential nutrients that the animals need but cannot make themselves. These discoveries open up possibilities for using special supplements (probiotics) or special foods (prebiotics) to improve animal health on fish farms.

This review brings together scattered research that scientists have been doing for years. Previous studies looked at individual species or specific bacteria, but this comprehensive review shows the bigger picture of how these relationships work across many different aquatic animals. It confirms what scientists suspected—that gut bacteria are just as important in aquatic animals as they are in humans and land animals.

Since this is a review of other studies rather than a new experiment, it’s limited by the quality and completeness of previous research. Some aquatic species have been studied much more than others, so we know more about some animals than others. Additionally, much of the research has been done in laboratory settings, which may not perfectly reflect what happens in nature or on real fish farms. More research is needed on how to practically use this knowledge to improve fish farming.

The Bottom Line

Fish farmers should consider monitoring and managing the gut health of their animals through diet and possibly probiotics (good bacteria supplements). While the evidence is promising, these strategies are still being developed and tested. Consumers interested in sustainable seafood should look for farms that are investing in animal health and welfare. Confidence level: Moderate—the science is solid, but practical applications are still being refined.

Fish farmers and aquaculture companies should care most about this research, as it could improve their operations. Environmental advocates should care because healthier farmed fish means more sustainable food production. Consumers who eat farmed fish and shellfish should care because it could affect the quality and healthfulness of their food. Researchers studying fish health, nutrition, and disease should definitely follow this work.

Changes to fish farming practices based on this research would likely take months to years to show results. If farmers adjust diets or add probiotics, they might see improvements in animal growth within weeks to months, but long-term benefits like better disease resistance would take longer to measure.

Want to Apply This Research?

  • If you’re interested in aquaculture or sustainable seafood, track the types of farmed fish and shellfish you consume and note any information about how they were raised. Over time, you could monitor whether you notice differences in quality or freshness between products from farms using different practices.
  • Use the app to research and choose seafood from farms that prioritize animal health and sustainable practices. Set a goal to learn about one new sustainable seafood source per month, or track your consumption of farmed versus wild-caught seafood to make more informed choices.
  • Create a long-term tracking system for your seafood purchases that notes the source and farming method. This helps you identify which producers are investing in better practices and supports the market shift toward more sustainable aquaculture. You could also track any digestive or health changes if you’re consuming more sustainably-raised seafood.

This article summarizes scientific research about gut bacteria in farmed fish and shellfish. It is for educational purposes only and should not be considered medical or nutritional advice for humans. While this research may eventually lead to improvements in farmed seafood quality, individual results may vary. If you have specific health concerns related to seafood consumption or allergies, consult with a healthcare provider. The practical applications of this research are still being developed and tested in real-world farming conditions.