The objective of this trial was to assess the impact of dietary B. coagulans (BC) and/or β-glucan (βG) supplements on growth, serum biochemical and hematological indices, antioxidant activity, immune parameters, digestive enzyme, and immune-related gene expression of seabream fingerlings (Sparus aurata) under sub-optimal temperature. A total of 405 healthy seabream fingerlings with an average weight of 22.95 ± 1.2 g were randomly allocated equally into 27 enclosures (hapa), with 15 fish per hapa. Nine fish groups were fed balanced diets containing 45% crude protein and 488 MJ/kg Gross energy, and supplemented with tested levels of BC (0.0, 1 or 2g/kg diet) or βG (0.0, 0.5 or 1g/kg diet), and their combined doses for 12 weeks then subjected to suboptimal temperature for two additional weeks. The results showed that the group fed a diet supplemented with 2g of BC and 1g of βG per kg diet exhibited higher specific and relative growth rates compared to the control group. Also, the same treated groups recorded the lowest mortality rate. Meanwhile, the groups supplemented with BC alone or in combination with βG significantly improved all estimated biochemical and hematological parameters compared to the control group. Similarly, the groups supplemented with BC and/or βG showed significant improvements in immunological parameters such as lysozyme, immunoglobulin M (IgM) levels, phagocytic index, and phagocytic activity. At the same tend, the dietary treatments significantly improved antioxidant capacity indices (CAT, MDA, and SOD), lipid profiles (triglyceride, cholesterol, glucose), cortisol concentrations, and gene expressions. In conclusion, the research findings indicate that the use of BC and/or βG supplements enhances the growth and boosts the resistance of seabream fingerlings against the negative impacts of sub-optimal temperatures.