In New Caledonia, shrimp hatcheries are confronted with mass mortality in the larval stages, a phenomenon
poorly understood as no specific causative agent has been identified. This has resulted in an excessive use of prophylactic
antibiotics, although their adverse effects in aquaculture are notorious. The present work was thus
aimed at selecting potential probiotic strains for penaeid hatcheries.
From a pool ofmore than 400 marine bacterial isolates sampled fromthe local marine environment seven strains
exhibited in vitro antagonistic activity toward Vibrio harveyi. These isolates were characterized both phenotypically
and genotypically using a biochemical approach and 16S rDNA sequencing. Six out of these seven strains
were found to belong to the genus Pseudoalteromonas, the last one belonging to the Vibrionaceae family and related
to the Harveyi clade. Selected probiotic candidateswere individually tested for antagonistic activities in vitro
using a green fluorescent protein (GFP)-labeled transconjugant of V. harveyi and for inherent pathogenicity toward
cultured shrimp larvae at two different developmental stages. This approach enabled rapid processing
and selection of candidates to be tested in our experimental hatchery. Four different experiments were conducted
to test candidate strains either alone or in combination. Repeated trials showed that postlarval survival was
significantly improved by adding the strain NC201 individually to the rearing water compared to unchallenged
controls. The analysis of immune-related gene expressions showed that the Litsty PEN3 transcript abundance
of larvaewas significantly increased after being reared in probiotic-containingwater; however no significant difference
in lysozyme gene expression was recorded in this study. Together, these results open new insights into
the use of these strains as potential substitutes to antibiotherapy in shrimp larval rearing in New Caledonia