Modern Approaches to Investigating the Effectiveness of Probiotics in Aquaculture

This review summarizes the available scientific data on the use of probiotics of different microbiological compositions in aquaculture, showing the effects of probiotics at physiological, tissue, and cellular levels, including those assessed by morphometric methods. Additionally, this paper systematizes data on the objects of study, the most commonly used probiotics, their concentrations, and research methods. It was found that the most studied aquaculture species in the use of probiotics are Oreochromis niloticus (35.9%), Oncorhynchus mykiss (6.2%), and Cyprinus carpio (4.6%). Experiments on these species are usually conducted under controlled conditions (pools, aquariums, RAS), and the duration of experiments varied from 20 to 140 days. The most frequently used microorganisms as probiotics are bacteria of the genera Bacillus (41.6%) and Lactobacillus (24.3%); the remaining 34.1% are other microorganisms of allochthonous or autochthonous origin. In most studies, the effect of probiotics was observed at concentrations of 1 × 10⁶ to 1 × 10⁹ CFU/g feed. Probiotics show varying efficacy, most often positively affecting growth performance, activity of digestive enzymes, gut microbiome, expression of genes associated with immunity, and resistance to pathogens. In most cases, probiotics had no effect on tissue nutrient composition and hematologic, biochemical, and immunologic parameters. Among the histomorphometric methods used when studying probiotics, the most frequently examined indicators are those characterizing the morphology of villi, layers composing the intestine, and the composition of immunocompetent cells, microvilli, and goblet cells. The response to probiotic exposure was most often noted in villus height, number of goblet cells, villus area, number of intraepithelial lymphocytes, and microvilli area of intestinal epithelial tissues. Most authors agree on the need to use a systematic approach to study probiotics.