Preservatives are substances added to food to stop or minimise deterioration caused by the presence of different types of micro-organisms (bacteria, yeasts, and moulds) and/or the exposure to light, oxygen, or metals, maintaining the nutritional value and extending the shelf life of the food.

Nearly one-third of the caught fish is not used for direct human consumption but processed into fishmeal or fish oil for animal feed.

Fishmeal is the product obtained by grinding and drying whole fish, parts of fish, or waste from the canning industry, from which some of the oil may have been extracted. Mainly pelagic species are used.

Fish is extremely perishable. Its deterioration begins at the time of capture due to the action of its own enzymes (tissue and digestive), which facilitates microbial activity in the decomposition process.
In addition, the characteristics of their lipid composition make fish very susceptible to oxidation and consequent rancidity. However, storage at low temperatures in dark places and anaerobic conditions reduces the risk of oxidation of bulk fish.

To stop the decomposition process of caught fish destined for fishmeal and to store the fish at low temperatures, some antimicrobial preservatives must be added.

These can be divided into two groups:

Chemical preservatives => organic acids and their salts (formic, acetic, benzoic, etc.), sodium sulphite, sodium nitrite.
Although they are inexpensive and easy to apply, there are several drawbacks, such as toxicity, carcinogenic effect, and corrosiveness, which is why their use is restricted in many countries.

Natural preservatives => are derived from microorganisms (nisin, reuterin), plants (essential oils, extracts) or animals (lysozymes, lactoperoxidases).

To be cost-effective, they must have a broad bactericidal and fungicidal spectrum, must be non-toxic and perform at low concentrations.

The greatest risk of fishmeal is its high susceptibility to oxidation due to the chemical properties of its fats (long-chain polyunsaturated fatty acids). During both processing and storage, the formation of peroxides, free radicals, aldehydes and polymers of fatty acid can occur, which decrease the nutritional value of the fishmeal and the food containing it.

In the case of fishmeal, the use of the preservatives described above, to avoid contamination by microorganisms, must be accompanied by the addition of antioxidants such as ethoxyquin, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tocopherols.