Impact of Ecobiol plus ® feed additive on growth performance, physiological response, oxidative status and immunological status of Nile tilapia (Oreochromis niloticus) fingerlings challenged with Aeromonas hydrophila.

This research investigates the effects of dietary supplementation with Ecobiol plus (Bacillus amyloliquefaciens CECT5940) on the growth performance, physiological responses, oxidative stress, and immune status of Nile tilapia (Oreochromis niloticus) fingerlings revealed to Aeromonas hydrophila. A total of 525 Nile tilapia fingerlings, averaging 30.00 ± 5.00 g in initial weight, were randomly divided into four groups (control and three experimental groups), each with three replicates of 25 fish. Ecobiol plus was integrated in the diet at concentrations of 0.0 (control), 0.1, 0.2, and 0.4 g/kg feed. Fish were fed at 3% of their biomass daily, with biweekly adjustments based on growth. The feeding trial lasted 8 weeks, followed by a 15-day challenge with Aeromonas hydrophila to evaluate immune responses and survival outcomes. The group receiving 0.4 g/kg of Ecobiol plus exhibited the most significant improvements in growth performance, including higher weight gain, specific growth rate, and feed conversion efficiency (p < 0.05). Blood and biochemical assessments indicated increased hemoglobin, total protein, and globulin levels, reflecting improved physiological and immunological conditions. Additionally, lysozyme activity and phagocytic response were markedly enhanced, demonstrating the probiotic's immune-boosting potential. Histopathological evaluations revealed reduced gut, gills, and hepatopancreas lesions, especially in groups with higher supplementation levels. Fish in Group T4, fed with 0.4 g/kg Ecobiol plus, achieved the best growth performance, with a final weight of 77.96 ± 5.53 g, a weight gain of 42.46 ± 3.18 g, and a specific growth rate (SGR) of 1.51%/day, compared to the control group (T1) with a final weight of 75.26 ± 3.87 g, weight gain of 35.76 ± 2.08 g, and SGR of 1.24%/day. Survival rates considerably increased in the treated groups, with T4 exhibiting the highest rate of 96.00%, followed by T2 (94.68%), T3 (92.00%), and T1 (81.32%). Additionally, the LD50 of A. hydrophila was determined to be 3 × 10⁷ CFU/mL, underscoring the protective effect of Ecobiol plus in enhancing fish immunity and resilience against bacterial challenges. These results suggest that Ecobiol plus can be a natural, antibiotic-free additive to strengthen growth and disease resistance in Nile tilapia. The optimal inclusion level of Ecobiol plus is 0.4 g/kg for maximum benefit.