Exploring the Interactive Effects of Thymol Oil and <i>Pediococcus acidilactici</i> : Moving Towards an Enhanced Performance, Hematology, Immunity and Gut Histology of Nile Tilapia ( <i>Oreochromis niloticus</i> )

Abstract An 84-day experimental trial was conducted to investigate the effects of dietary thymol and/or P. acidilactici on growth performance, intestinal digestive enzymes, bacterial counts, intestinal histomorphometric indices, hemato-biochemical indices, and antioxidant responses in Nile tilapia, Oreochromis niloticus . A basal diet (30.34 g kg −1 of crude protein) and isocaloric diet (19.21 MJ kg −1 gross energy) was used to form the experimental treatments. Control group was the basal diet without additives and the other three formulated diets were supplemented with 2.32 thymol mg kg −1 diet or P. acidilactici at 2×10 9 CFU kg− 1 (probiotic; pro), and their mixture. A total number of 300 healthy fingerlings (initial average weight 4.51±0.01 g) were randomly allocated into four groups (25 fish for each group in triplicates). The results showed that the best values of growth and feed conversion ratio (FCR) were recorded in fish fed diet containing a mixture of thymol + P. acidilactici . The activity of endogenous enzymes including amylase, lipase, trypsin, and chymotrypsin was substantially boosted (P≤0.05) by diets supplemented with thymol + P. acidilactici . Furthermore, fish fed diet supplemented with thymol + P. acidilactici had greater villi width, villi height, goblet cells, absorption area, muscularis mucosa, and muscularis. Diets supplemented with a mixture of thymol + P. acidilactici substantially improved hematological markers. The diets supplemented with thymol + P. acidilactici improved the activities of catalase (CAT), glutathione peroxidase (Gpx), superoxide dismutase (SOD), and total antioxidant capacity (TAC) versus basal diet. In conclusion, the synergetic effect between thymol + P. acidilactici ameliorated the growth, feed efficiency, intestinal digestive enzymes, intestinal histological morphometric, hemato-biochemical indices, and antioxidant responses of Nile tilapia.