Synergistic dietary supplements of Lactobacillus brevis and trans-cinnamic acid improved growth, immune response, and disease resistance in common carp.

This research investigated the dietary effects of Lactobacillus brevis (LB) and/or trans-cinnamic acid (TrCA) on growth, immune and antioxidant responses, expression of immune-related genes, and resistance to Aeromonas hydrophila infection in common carp (Cyprinus carpio). Four diets were formulated with no additives (the control; T0), or with L. brevis at 1 × 1010 CFU/g feed (T1), TrCA at 0.5 g/kg feed (T2), and a combination of L. brevis and TrCA (T3). A total of 240 (mean initial weight: 22.80 ± 1.03 g) were stocked into twelve 200-L tanks (20 fish per tank) to represent four dietary treatments in triplicates and feed with four mentioned diets for eight weeks. Following the feeding trial, fish were challenged with A. hydrophila infection and monitored for survival over additional 14 days. It is noted that fish growth, antioxidant, and immune performances were significant (P < 0.05) affected by dietary LB and TrCA. Fish received T1-T3 diets exhibited significantly (P < 0.05) higher growth performance compared to the control group (T0). Digestive enzymes activities (proteases, lipase, and α-amylase) were significantly (P < 0.05) enhanced in T1, T2, and T3 compared to T0. Immunological parameters, including lysozyme activity, total immunoglobulin levels, and ACH50, as well as antioxidant enzymes (SOD, CAT, and GPx) activities were elevated in T1-T3 groups relative to the control one (P < 0.05). No marked changes were observed in MDA levels among treatments. The expression of immune-related genes (TNF-α, IL-6, IL-8, and IL-10) in mucosal and intestinal tissues was significantly (P < 0.05) upregulated in all supplemented groups, and their highest expressions were observed in T3. The bacterial challenge assay demonstrated that fish in T3 had the lowest mortality rate (43.3%), followed by T1 and T2, meanwhile the highest mortality rate was recorded in the control (T0) group (70%). These findings indicate that the combined dietary inclusion of both L. brevis and TrCA synergistically enhances growth, immune competence, antioxidant capacity, and resistance to possible A. hydrophila infection in common carp.