Antimicrobials in aquaculture

Antimicrobials destroy bacteria, viruses, fungi, algae, and other microbes. The cells of bacteria (prokaryotes), such as salmonella, differ from those of higher-level organisms (eukaryotes), such as fish. Antibiotics are chemicals designed to either kill or inhibit the growth of pathogenic bacteria while exploiting the differences between prokaryotes and eukaryotes in order to make them relatively harmless in higher-level organisms. Antibiotics are constructed to act in one of three ways: by disrupting cell membranes of bacteria (rendering them unable to regulate themselves), by impeding DNA or protein synthesis, or by hampering the activity of certain enzymes unique to bacteria.

Antibiotics are used in aquaculture to treat diseases caused by bacteria. Sometimes the antibiotics are used to treat diseases, but more commonly antibiotics are used to prevent diseases by treating the water or fish before disease occurs. While this prophylactic method of preventing disease is profitable because it prevents loss and allows fish to grow more quickly, there are several downsides.

The overuse of antibiotics can create antibiotic-resistant bacteria. Antibiotic-resistant bacteria can spontaneously arise when selective pressure to survive results in changes to the DNA sequence of a bacterium allowing that bacterium to survive antibiotic treatments. Because some of the same antibiotics are used to treat fish that are used to treat human disease, pathogenic bacteria causing human disease can also become resistant to antibiotics as a result of treatment of fish with antibiotics. For this reason, the overuse of antibiotics in treatment of fish aquaculture (among other agricultural uses) could create public health issues.

The issue has two sides. In some foreign countries, clean water supplies for aquaculture are extremely limited. Untreated animal manure and human waste are used as feed in shrimp farms and tilapia farms in China and Thailand, in addition to the collection of waste products accumulating from inadequate sewage treatment. In order to prevent the spread of bacteria and disease in contaminated water, some foreign fish farms put U.S.-banned antibiotics into their fishmeal. However, because the more stringent growing regulations in the US increase the price of food, imports from nations without these regulations are increasing based on price and profit.

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