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Evaluation of phenolic extract of licorice roots in diets of Nile tilapia (Oreochromis niloticus)

Aims The aims of this study were to evaluate the effect of methanolic extract of licorice roots (MELRs) as a feed additive on the growth performance, feed utilization, and innate immunity of Nile tilapia (Oreochromis niloticus), and to screen the phenolic compounds contained in the different MELRs through reverse-phase high-performance liquid chromatography (HPLC). Background Licorice is doubtless one of the most popular medicinal plants, with its roots being the most used part. Particularly, the species Glycyrrhiza glabra L. has well-known therapeutic properties, which have been documented since the Egyptian age. Materials and methods MELR was prepared as follows: in a typical experiment, 500 g of the plant was dried at room temperature. The dried plant was defatted separately with n-hexane in a Soxhlet apparatus for 15 h. The plant residue was then extracted with methanol in a Soxhlet apparatus for 20 h. The obtained data were analyzed using one-way procedure SPSS according to the following model: Yij = μ+Ti +eij , where μ is the over mean, Ti is the fixed effect of the rocket supplementation (1…4), and eij is random error. The differences between the experimental groups were determined using Duncan′s multiple range test. Results and discussion Screening the phenolic compounds contained in the different MELR achieved through reverse-phase HPLC analysis showed 21 phenolic and flavonoid compounds. The MELR supplementation enhanced fish growth compared with the control diet, and the highest fish performance was obtained at 0.04% MELR level. Supplementation with MELR was found to have an antibacterial activity antagonistic to pathogenic bacteria Aeromonas jandaei infection in fish. It is recommended that 0.04% MELR be used as a feed additive for Nile tilapia to enhance its growth performance, health, and innate immunity. Conclusion This study was carried out to evaluate the effect of MELRs as a feed additive on the growth performance, feed utilization, and innate immunity of Nile tilapia. MELR enhances fish growth rate, feed utilization, and innate immunity. The highest fish growth was obtained when fish were fed a diet containing 0.04% extract.