سعید حاجی رضایی

Probiotics are microbial cells with multifunctional properties including immunostimulatory function in their host. Today, probiotics are widely used for controlling diseases in aquaculture, especially for rainbow trout, Oncorhynchus mykiss, as the most important commercial cold-water fish in the world. So far, many studies have been conducted on the effect of probiotics on the immune system of rainbow trout, but due to different experimental conditions, these results are different and sometimes inconsistent. Therefore, the aim of the present study was to perform a systematic review and meta-analysis to eliminate inconsistencies and to clarify the results related to some immune parameters in rainbow trout. This study is the first meta-analysis study of probiotic-induced effects on the immune system of rainbow trout. In order to perform meta-analysis, four Internet databases, PubMed, Scopus, ISI Web of Science and Google Scholar were systematically searched until 27/03/2020 and after receiving related articles, effect sizes related to 10 outcomes including serum and plasma lysozyme activity, ACH50 activity, Ig activity, serum complement activity, phagocytosis activity, serum total protein activity and respiratory burst activity were evaluated by SMD and Hedges' g statistic and 95% CI was calculated from a random effects model. The SYRCL’S risk of bias tool for animal study was also used to assess the quality of the studies. Meta-analysis was performed for 36 studies by 499 experiments. The effect of probiotics on immunity components was as follows: serum lysozyme activity (p < 0.05), plasma lysozyme activity (p > 0.05), Serum ACH50 activity (p < 0.05), Plasma ACH50 activity (p < 0.05), serum immunoglobulin activity (p < 0.05), plasma immunoglobulin activity (p < 0.05), total serum protein activity (p < 0.05), serum complement activity (p < 0.05), phagocytic activity (p < 0.05) and respiratory burst activity (p > 0.05). In conclusion, the results of the present study showed that, except plasma lysozyme activity and burst activity, probiotics could enhance immune system of rainbow trout.