Modulation of digestive enzyme activity, blood health, oxidative responses and growth-related gene expression in GIFT by heat-killed Lactobacillus plantarum (L-137)

The current study was performed to investigate the effects of dietary heat-killed Lactobacillus plantarum (HK L-137) on growth, digestive enzyme activity, intestinal morphology and oxidative status in genetically improved farmed tilapia (GIFT). For 12 weeks, fish were fed a control diet (HKLO) or a diet supplemented with HK L-137 at a concentration of 50 (HKL50), 100 (HKL100) or 1000 (HKL1000) mg kg(-1) feed. At the final sampling, the HKL100 group had significantly (P < 0.05) increased performance parameters (FBW, WG, SGR and FER) compared to the control group, while the HKL50 and HKL1000 groups showed weaker improvements. Mucosal thickness and villus length were significantly (P < 0.05) increased in the HKL50 and HKL100 groups in the anterior, middle and posterior intestine, but muscle thickness was significantly (P < 0.05) improved only in the anterior and middle intestine. Amylase, lipase and protease activity was significantly (P < 0.05) increased in fish fed 50 or 100 mg HK L-137 per kg diet compared to control fish. Significant modulation of blood haematocrit, haemoglobin levels, and RBC and WBC counts (P < 0.05) occurred in fish fed HK L-137, while total cholesterol and GPT were decreased by HK L-137. Furthermore, antioxidative enzyme (SOD and CAT) activity were significantly (P < 0.05) higher in the HKL100 group than in the control group, while MDA levels were lower. Furthermore, fish fed HK L-137 showed enhanced total serum protein and IgM levels. Interestingly, qRT-PCR revealed significant (P < 0.05) upregulation of the growth-related gene IGF-I and the glucose regulation gene G6PD but downregulation of the fatty acid synthase (FAS) gene in all HKL groups compared to the control group. Thus, we conclude that the use of HK L-137 is an efficient strategy to achieve economically feasible and sustainable tilapia production.