Mariya Sewaka

Exopolysaccharide (EPS)-producing bacteria were isolated from the intestines of freshwater fish as prebiotics. Among the isolates, Bacillus sp. P1 was the potent EPS producer, with a high EPS production, and was then identified as Bacillus subtilis P1 based on 16S rRNA and biochemical characteristics. The produced microbial EPS was characterized by its functional groups by FTIR, showing a 90.20% correlation to inulin, while the EPS molecular weight was approximately 10⁵ Da with a high PDI (>1.5). Moreover, the EPS from B. subtilis P1 was assessed for prebiotic properties by growing probiotic bacteria, and significant cell growth occurred in sugar-free TSB with 0.5% EPS (p < 0.05). EPS exhibited approximately 55.37% DPPH radical scavenging at 20 mg/mL and inhibited certain fish pathogens at 400 μg/mL (10–13 mm inhibition zone). Low EPS cytotoxicity was confirmed (Oreochromis niloticus) diet supplementation. Nile tilapia growth and immune response were monitored after feeding with control (C), basal diet (BD), and treatment (T): BD + EPS 5 g/kg. In the T-group, the weight gain (WG), % specific growth rate (SGR), and average daily gain (ADG) significantly increased compared to the control (p < 0.05) by week 4, with no negative effects on blood chemistry parameters. Lysozyme activity and respiratory burst activity in T-groups were significantly higher than the control (p < 0.05), with a 50% RLP survival rate of Nile Tilapia infected by Aeromonas veronii in the T-group after a two-week challenge. On the other hand, the proximate analysis revealed higher protein content in the T-group. These findings suggest that EPS from B. subtilis P1 in fish diets efficiently supports fish growth and stimulates innate immune response in Nile Tilapia, thus showing potential as the immunobiotics for aquaculture.

Exopolysaccharide (EPS)-producing bacteria were isolated from the intestines of freshwater fish as prebiotics. Among the isolates, Bacillus sp. P1 was the potent EPS producer with a high EPS production and was then identified as Bacillus subtilis P1 based on 16S rRNA and biochemical characteristics. The produced microbial EPS was characterized its functional groups by FTIR, showing a 90.20% correlation to inulin while the EPS molecular weight was approximately 105 Da with a high PDI (>1.5). Moreover, the EPS from B. subtilis P1 was assessed for prebiotic properties by growing probiotic bacteria and the significant cell growth occurred in sugar-free TSB with 0.5% EPS (p<0.05). EPS exhibited approximately 55.37% DPPH radical scavenging at 20 mg/mL and inhibited certain fish pathogens at 400 μg/mL (10-13 mm inhibition zone). EPS cytotoxicity was confirmed (<1% hemolysis) prior to use as immunobiotics in Nile Tilapia (Oreochromis niloticus) diet supplementation. Nile tilapia growth and immune response were monitored after feeding with control (C): Basal Diet (BD) and treatment (T): BD + EPS 5 g/kg. In the T-group, WG, %SGR, and ADG significantly increased compared to control (p<0.05) by week 4th, with no negative effects on blood chemistry parameters. Lysozyme activity and respiratory burst activity in T-groups were significantly higher than control (p<0.05), with a 50% RLP survival rate of Nile Tilapia challenged with Aeromonas veronii in the T-group within two weeks. On the other hand, for the proximate analysis revealed higher protein content in the T-group. These findings suggest that EPS from B. subtilis P1 in fish diets efficiently supports fish growth and stimulates innate immune responses in Nile Tilapia, thus showing potential as the immunobiotics for aquaculture.

Nanotechnology can enhance nutrient delivery and bioavailability; hence, it has recently been considered the most practical alternative technology for nutritional supplements and disease control in fish farming. The present study was designed to evaluate the effects of mangosteen peel extract loaded in nanoemulsion (MSNE) on the inhibition of A. veronii (in vitro) and in vivo growth performance, serum biochemical parameters, the immune response, and the disease resistance of Nile tilapia (Oreochromis niloticus) against A. veronii challenge. The particle size, polydispersity index, and particle surface charge of MSNE were 151.9 ± 1.4 nm, >0.3, and −30 mV, respectively. Furthermore, MSNE, mangosteen peel extract (MPE), and nanoemulsion (NE) improved the antimicrobial activity against A. veronii. Fish fed MSNE, MPE, and NE-supplemented diets had a significantly lower (p < 0.05) feed conversion ratio (FCR) and higher specific growth rate (SGR) than fish fed the control diet. Furthermore, the MSNE had significantly higher serum glucose and protein levels than the control group in Nile tilapia. Total immunoglobulin, serum lysozyme, alternative complement activity, and survival of Nile tilapia fed with MSNE were significantly higher (p < 0.05) than the control diet. Therefore, MSNE has the potential to be employed as a supplement in sustainable Nile tilapia farming.