This experiment aimed to determine the growth, feed efficiency, blood hematological and biochemical indices, intestinal structure, antioxidant activities, immune responses, and regulation of related genes in seabream (Sparus aurata L.). The fish were divided equally into nine separate groups (each with three replicates). The first group received a basal diet without any feed additives (CTR). While the remaining eight groups were afforded a basal diet supplemented with B. coagulans at 1 g (BC1) or 2 g (BC2) per kg of diet and β-glucans at levels of 0.5 g (βG1) or 1 g (βG2) per kg of diet. Additionally, there were combination groups of 1 g B. coagulans per kg of diet in combined with 0.5 g β-glucans (BC1+ βG1) per kg of diet, 1 g B. coagulans per kg of diet in mixed with 1 g β-glucans (BC1+ βG2) per kg of diet, 2 g B. coagulans per kg of diet in combined with 0.5 g β-glucans (BC2+ βG1) per kg of diet, and 2 g B. coagulans per kg of diet mixed with 1 g β-glucans (BC2+ βG2) per kg of diet. The experimental design followed a 2 × 2 factorial arrangement over 12 weeks. The growth trial results indicated a significant improvement in all measured growth and feed efficiency metrics when BC2 and βG2 were used together compared to the control and other treated groups (P ≤ 0.001). Additionally, there were significant increases in MCHC, WBC, lymphocytes, and monocytes in all fingerlings afforded diets supplemented with βG alone or in mixture with BC at any level compared to other treated groups (P ≤ 0.05, 0.01, or 0.001). Meanwhile, the interaction between BC2 and βG2 significantly suppressed liver enzyme levels (AST and ALT) and increased total protein and globulin contents compared to other experimental groups (P ≤ 0.01). The interaction between BC2 and βG2 resulted in significant improvements in immune responses (lysozyme, phagocytic activity, phagocytic index, and immunoglobulin M levels) and all measured antioxidant indices (decreased malondialdehyde (MDA) levels, while increasing glutathione (GPX), catalase (CAT), and superoxide dismutase (SOD) contents) promoted compared to the other groups. In addition, fish receiving higher amounts of both BC and βG demonstrated higher triglyceride and cortisol levels, as well as lower glucose and cholesterol levels compared to other treatment groups. Furthermore, the intestinal structure of fish group-fed diets supplemented with βG2 + BC2 exhibited a remarkable increase in villus length and numerous branching throughout the intestinal tissues, with few lipid vacuoles and a thin muscular layer, along with pronounced mucosal and submucosal folds. Similarly, diets enriched with high levels of both BC and βG demonstrated significantly downregulated the HSP70 gene expression and upregulated the IL-1β and IGF-1 gene expression (P ≤ 0.05 or 0.01). In conclusion, it could be recommended that enriching seabream fish feed with 1 g βG per kg of diet along with 2 g BC per kg of diet could promote growth, support oxidative status, and stimulate immune responses.