Will Perry, lead author and Bangor University School of Natural Sciences Ph.D. student explains: "The gut microbiome is vital for healthy fish growth and plays a role in fighting disease. The microbiome contributes to the fish's ability to digest and make use of fatty acids and vitamins.

However, the fact that fish are farmed can affect their gut microbiome, through changes in diet, the introduction of other inputs to maintain health, like antibiotics, and high population densities.

As with humans, a dose of antibiotics can mess around with the microbiome in the gut and can harm helpful bacteria. Over-use of antibiotics can also lead to antibiotic resistance in fish as with animals and humans.

One response is the development of alternatives to antibiotics, including the application of vaccines, through injecting the fish, immersing the fish in the vaccine, or feeding the fish the vaccine.

Alternative proteins are also increasingly used to feed fish, including those derived from plants and insects. But these have different effects on the microbiome, and benefits can vary between different fish species, with scope for further research."