Abstract <p>Probiotic preparations have proven effective in various areas of agriculture, including aquaculture. Their use allows avoiding the spread of resistant strains of pathogenic microorganisms in aquaculture farms, as occurred with the uncontrolled use of antibiotics. However, preparations from live bacteria have a limited shelf life and are difficult to manufacture. Bacterial probiotics are used mainly in freshwater aquaculture, including cultivation of larval stages of aquatic organisms. Microalgae cultures have almost all the same properties as bacterial probiotic preparations, but they also increase the level of dissolved oxygen in water and improve immunity and resistance to pathogenic bacteria and fungi. Microalgae are safer for larval stages and juvenile aquatic organisms at high concentrations. Thus, live cultures of microalgae can be used as probiotics in cultivation of aquatic organisms, which represents a promising direction.</p>