Evaluations of lactic acid bacteria as probiotics for juvenile seabass Lates calcarifer

Abstract

Lactic acid bacteria (LAB) were isolated from adult, wild-caught and farmed seabass (Lates calcarifer) intestines for evaluation as possible probiotics using the well agar diffusion method. Five LAB isolates (designated as LAB-1–5) were found to inhibit Aeromonas hydrophila, a known seabass pathogen. Median lethal concentrations (LC50) of A. hydrophila on juvenile seabass were measured in aquaria. Median lethal concentration values of 7.76, 7.47 and 7.26 log10 CFU mL−1 for 72, 96 and 120 h, respectively, were found. Juvenile seabass (0.6±0.2 g) were cultured in aquaria and fed individual LAB-1–5 fortified feeds with 7 log10 CFU g−1 LAB. Seabass fed LAB-4 fortified feed had significantly greater growth (P<0.05) than fish fed other feeds. Seabass fed LAB-4 also had greater survival, but this was non-significant (P<0.05). Challenge tests of LAB-4 fed seabass with A. hydrophila at ∼7 log10CFU mL−1 yielded significantly greater survival compared with control seabass (P<0.05). Aeromonas hydrophila infections in seabass were confirmed by observing disease manifestation and by immunohistochemistry techniques. LAB-4 was preliminarily identified using lactic acid analysis, biochemical and physical characteristics. It was further identified using 16S rDNA sequencing. LAB-4 was identified as Weissella confusa (identity of 99%). GenBank accession number for the 16S rDNA sequence for LAB-4 was AB023241.