| Summary: | The aquaculture industry is turning to the use of probiotics to promote good health among fish
and improve their productivity. Among the different types of probiotics, host-derived
probiotics promise improved efficacy towards specific fish species, compared to commercial
or terrestrial-derived probiotics. Hence, to fully utilise the benefits of host-derived probiotics,
this study aimed to identify and characterise potential probiotic strains of fish gut origin that
can improve the disease resistance of Jade Perch, one of the newly farmed fish species in
Singapore. Potential probiotics were isolated from the gut of five adult Jade Perches and tested
for their antimicrobial properties against fish pathogens including Aeromonas sobria,
Streptococcus iniae, and Streptococcus agalactiae. The final probiotic candidate was identified
using 16S rRNA sequencing and Whole-Genome Sequencing. It was also characterised in
terms of its biosafety and viability in different harsh conditions. The isolate that can inhibit the
growth of A. sobria and S. iniae was identified to be Enterococcus hirae. It contains no
virulence genes, antibiotic resistance genes, and mobile genetic elements. E. hirae presents
good viability in environments of pH 3.0 and above, and with temperatures of 30°C to 45°C. It
is found to be viable in simulated intestinal fluid, but not in simulated gastric fluid. The use of
E. hirae as a probiotic for Jade Perch is promising as it is both safe and effective. More work
is required, however, to explore suitable encapsulation techniques to protect the probiotic
against a very low pH environment and gastric fluids. Future in vivo feeding trials are also
recommended to test for its efficacy as a probiotic for Jade Perch under natural conditions.
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