A key element in the diagnosis of bacterial infections in fish is the rapid identification of the etiological agent of the disease and drug resistance testing. Traditional methods of identifying the bacteria that cause fish diseases are often slow and/or expensive. MALDI-TOF MS is a well-established, rapid, accurate and cost-effective method based on protein profile analysis for the identification of bacterial pathogens in human and veterinary laboratories, and has now found application in the diagnosis of bacterial infections in fish. The method identifies microorganisms based on their protein profile, which is then compared with reference spectra stored in databases. Since not all bacterial fish pathogens are included in commercial databases, libraries are usually created locally for the relevant reference strains/species. As studies have shown, MALDI-TOF MS is suitable for the specific identification of many bacterial fish pathogens enabling rapid diagnosis of infections