Effects of dietary synbiotics and biofloc meal on the growth, tissue histomorphology, whole-body composition and intestinal microbiota profile of Nile tilapia (Oreochromis niloticus) cultured at different salinities

Abstract

In this study, the effects of synbiotic and biofloc meal on the growth performance, gastrointestinal microbiota diversification, proximate body composition, total gut bacterial counts, liver and intestinal histomorphology of Nile tilapia (Oreochromis niloticus) reared under different salinity levels were examined. Fishes with an initial weight of 21.52 ± 2.21 g were divided into three main groups (freshwater 0 ppt, brackish water 6 ppt, and marine water 18 ppt), each with triplicates of control and synbiotic groups. While the control groups were not supplemented with any feed additives, a single dose of combined dietary synbiotic and biofloc meal (probiotic mixture for 1 kg of feed: Lactobacillus Plantarum 10 ml 1.5 × 109 cob g−1, Saccharomyces boulardii 250 mg 5 × 109 cob g−1 and Lactobacillus acidophilus 25 mg 5 × 109 cob g−1, mannan oligosaccharides as prebiotic: 2 g kg−1 feed, and biofloc meal: 3 g kg−1 feed) has been added to the feeds of all the experimental groups. At the end of this trial, the highest final body weight (FBW) (42.70 ± 3.25 g) and weight gain (WG) (21.79 ± 5.07 g) were found in the freshwater group fed with synbiotic and biofloc meal-added feeds, while the lowest FBW (37.13 ± 5.79 g) and WG (15.65 ± 6.00 g) were recorded in the marine water control group (p < 0.003). Similarly, the lowest and highest FCR (1.17 and 2.00) were obtained in freshwater synbiotic and marine control groups, respectively (p < 0.05). In terms of survival rate, no significant difference (p > 0.05) was noted among the groups. Unlike the growth performance, which decreased with the increase of water salinity, the increase in salinity significantly improved the whole-body composition. Further, the supplementation of synbiotic and biofloc meal enhanced both gut bacterial count and whole-body composition. Brackish and marine water did not cause significant adverse effects on the digestive tract microbiota profile and tissue histomorphology. Based on this study's findings, adding synbiotics and biofloc meal to Nile tilapia diets is an effective strategy that can mitigate the potential adverse effects of salinity on growth and also improve gut microbiota, body composition and tissue histomorphology.