Isolation of <em>Lactobacillus plantarum</em> CMT1 from shrimp intestine and its effects on growth and survival of the whiteleg shrimp, <em>Litopeneaus vannamei</em>

Abstract

Probiotics are widely applied in aquaculture, which can improve the growth, survival and health of aquatic animals. The aim of this study was to isolate and evaluate a <em>Lactobacillus</em> strain from the intestine of healthy whiteleg shrimp, <em>Litopenaeus vannamei</em>. A total of 20 <em>Lactobacillus</em> isolates showed rod-shaped morphology, gram-positive, non-motile, non-spore forming, and catalase and oxidase negative. Among the isolates, strain CMT1 exhibited the highest antibacterial activity against <em>Vibrio parahaemolyticus</em> and extracellular enzyme activity, which was selected and identified as <em>Lactobacillus plantarum</em> CMT1 based on 16S rDNA gene sequencing. This strain was also chosen to evaluate its effects on growth and survival of the whiteleg shrimp as a feed supplement. Four different diets were prepared, including the control (a commercial diet without <em>L. plantarum</em> CMT1) and three different concentrations of <em>L. plantarum</em> CMT1, viz. T1 (10^6 CFU kg diet^-1), T2 (10^7 CFU kg diet^-1), and T3 (10^8 CFU kg diet^-1). After a 56-day feeding trial, the growth parameters in the T3 group had the highest values and showed a significant difference compared to the other groups. The survival rates of shrimp fed T2 and T3 diets were significantly higher than those in the control diet (p < 0.05). The lowest FCR value was recorded in the T3 group and showed a significant difference compared to the control group (p < 0.05). In addition, <em>Lactobacillus</em> counts in T2 and T3 groups increased significantly from day 28, which indicated that <em>L. plantarum</em> CMT1 could sustain its population in the intestine of shrimp. However, the total <em>Vibrio</em> sp. count in the T2 and T3 groups was significantly lower than that in the control group (p < 0.05). In conclusion, <em>L. plantarum</em> CMT1 could be used as a potential probiotic for shrimp aquaculture, and the recommended level of the probiotic strain CMT1 is 10^8 CFU kg diet^-1.