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.