Enhanced growth, antioxidant responses and resilience to Vibrio alginolyticus induced by Lactobacillus bulgaricus supplementation in Liza ramada

Abstract

This study tested five diets supplemented with Lactobacillus bulgaricus (LB; 0, 1, 2, 3, and 4 g/kg) (designated as CNT, LB LB1, LB2, LB3, and LB4) with the basal diet on growth, antioxidant capacity, hepatic and intestinal histoarchitecture, and resistance of Liza ramada to Vibrio alginolyticus infection. Fish (8.47 ± 0.40 g) were stocked in triplicate groups in hapas fixed in cement ponds and fed on freshly prepared test diets for 60 days. Fish-fed LB-supplemented diets demonstrated higher final weight (FBW), and specific growth rate (SGR) compared to the CNT group (ANOVA P < 0.0001), with the cubic trend for FBW and quadratic trend for SGR, as analyzed by the polynomial model. Similarly, higher feed intake and feed conversion ratio were found in groups fed LB-supplemented diets with a strong cubic trend with increasing dietary LB levels. The hepatic SOD (superoxide dismutase) and CAT (catalase) enzyme activities improved significantly in all LB groups while a significant increase in GPx (glutathione peroxidase) enzyme activity and decrease in MDA (malondialdehyde) levels were found in all dietary groups, except LB1 when compared to those fed CNT diet. The hepatic antioxidant responses were well fit with all polynomial models, but the cubic fit was highly significant in response to dietary LB levels. The intestinal and hepatic histoarchitecture showed normal and healthy structures across all treatments. The fish survival rate (55–70 %) improved significantly in fish fed 2–4 g/kg LB compared to the CNT group (15 %). To conclude, a dietary dose of 2–4 g/kg can be supplemented to bolster the infection resistance against pathogenic bacteria by enhancing growth, feed utilization, and antioxidant responses, potentiating its application as a functional additive to maximize the profitability of mullet farming.