The presence of lactic acid bacteria (LAB) favors the stabilization of intestinal flora, facilitates digestion, improves the assimilability of fodder, and has an immunomodulatory effect on the immune system. According to current research, the application of LAB following antibiotic treatment prevents the development of opportunistic bacteria inhabiting the digestive tract. In the study the potential probiotic properties of Lactobacillus plantarum strains, which can be administered as an alternative to antibiotic treatment in aquaculture, were investigated under in vitro conditions. The strains of L. plantarum were characterized for important properties such as the ability to grow in the presence of 10% fish bile, a tolerance of low pH, and antagonism to pathogens dangerous for fish such as Aeromonas salmonicida and Pseudomonas fluorescens; therefore, they meeting the criteria for strains with probiotic properties. In view of currently increasing resistance to antibiotics and a decrease of their efficiency, probiotic bacteria can serve to support immunity to infections in the future.