Effects of dietary yeast culture on growth performance, immune response and disease resistance of gibel carp (Carassius auratus gibelio CAS III)

A 50-day feeding trial was carried out to evaluate the partial replacement of fishmeal by yeast culture (YC) on growth performance, immune response and resistance against Aeromonas hydrophila in gibel carp CAS III (Carassius auratus gibelio). Four isonitrogenous and isoenergetic practical diets including a basal diet (the control diet containing 10% fish meal, D0) and three yeast culture diets (substituting 20%, 40%, 60% of the fishmeal in the basal diet, D20, D40 and D60, respectively) were formulated. Each diet was randomly allocated to quadruplicate fish groups (average initial body weight: 28.70 +/- 0.03 g) reared in a recirculating system. After the growth trial, bacterial challenge test was conducted. The results showed that no noteworthy variations in feed intake, growth performance and morphology indices were found among groups (P > 0.05). YC Supplemented diet exerted little significant influence on plasma parameters including triglyceride, glucose, creatinine, total protein and urea nitrogen compared with the control group (P > 0.05). No obvious variations were found in activities of plasma lysozyme, IgM, MPO and SOD before challenge test among dietary treatments (P > 0.05), whereas considerable higher value of the foresaid indicators was discovered in D40 after bacteria challenge (P < 0.05). Transcriptional levels of Toll like receptor 2 (TLR2), myeloid differentiation factor 88 (MyD88), Toll/IL-1 receptor domain-containing adaptor protein (TIRAP) and interleukin-1 beta (IL-1 beta) in spleen after challenge were significantly up-regulated in D40 compared with D0 (P < 0.05). Cumulative survival rate in D40 and D60 were significantly higher than those in D0 and D20 (P < 0.05). Taken together, yeast culture could be a suitable fishmeal alternative in diets of gibel carp and dietary inclusion of 4 g YC per 100 g diet enhanced the immunity and disease resistance of gibel carp partly via TLR2 pathway.