The cultivation of aquatic organisms such as fish, mollusks, and crustaceans requires constant bacterial monitoring, as diseases are no less a problem for aquaculture than for other livestock farming sectors. As the use of antibiotics becomes increasingly problematic, the use of bacteriophages in aquaculture is being considered as effective and environmentally friendly antimicrobial agents.

Antibiotics are easy-to-use, broad-spectrum antimicrobials that are widely used in aquaculture worldwide. However, antibiotics are associated with numerous problems: they destroy beneficial bacteria in aquatic environments along with pathogenic ones, and antibiotic-resistant bacteria are also on the rise. Large quantities of antibiotics entering aquatic environments pose a risk of developing and spreading antibiotic-resistant genes among bacteria, which can make it impossible to treat many dangerous human and animal diseases. To prevent this, many countries have restricted the use of antibiotics in agriculture and aquaculture.

Bacteriophages (phages)—bacterial viruses discovered over 100 years ago but abandoned due to the advent of antibiotics—are increasingly being used in medicine, veterinary science, agriculture, and the food industry. Phages are highly specific—they infect only a specific strain or species of bacteria and do not affect others. Phages are naturally occurring and therefore environmentally safe.

Read also: Plastic waste in the oceans is fueling the spread of antibiotic resistance.

Although the use of phages in aquaculture is still in the testing phase, it has enormous potential. Phages specific to a particular bacterium are relatively easy to find in nature, and this is significantly cheaper than developing a new antibiotic. Phages kill their target bacteria without harming other microorganisms. Phages reproduce as long as their targets are present in the environment, and when the latter are destroyed, the phages disappear. After phage application, no toxins or other traces of their activity remain. Bacteriophages can target antibiotic-resistant bacteria, bacteria in biofilms, and can also be used prophylactically.

The specificity of phages dictates certain aspects of their application: controlling several bacterial species simultaneously requires cocktails of phages specific to those species; bacteria can develop resistance to phages, so phage preparations require regular monitoring of their activity and strain renewal (selection of new active phages is not a problem).

Today, the use of phages in aquaculture is significantly hampered by the lack of an appropriate regulatory framework in Europe and the United States that would regulate the production of phage preparations.

Phages are being explored for both the treatment of bacterial infections and routine prophylaxis. It remains unclear which of these strategies offers the greatest advantages.

Scientists are striving to create ideal phage preparations—guaranteed to be lytic and safe for gene transfer between bacteria, as well as easy to produce and undemanding to storage conditions.

For more information on the use of bacteriophages in aquaculture, see the review in the journal Antibiotics *.

* Kowalska, JD; Kazimierczak, J.; Sowińska, PM; Wójcik, E. A.; Siwicki, A.K.; Dastych, J. Growing Trend of Fighting Infections in Aquaculture Environment—Opportunities and Challenges of Phage Therapy. Antibiotics 2020, 9, 301.