Bacterial community of Parvocalanus crassirostris nauplii and the potential of nauplii as a vector for early probiotic supply to fish larvae.

Objective: The copepod Parvocalanus crassirostris has recently increased its use as live food in marine fish hatcheries. Methods: To investigate the bacterial community of P. crassirostris nauplii and explore the potential use of nauplii as a vector for probiotics, adult copepods were reared with or without a probiotic consortium (Bacillus spp. and Lactobacillus spp.). Nauplii from both treatments were either enriched with probiotics or not, resulting in four treatments: control rearing and nonenriched, control rearing and probiotic enriched, probiotic rearing and nonenriched, and probiotic rearing probiotic enriched. A next‐generation sequencing analysis of the 16S ribosomal RNA gene was performed. Result: The bacterial community of nauplii without probiotics was dominated by the phyla Proteobacteria (mean ± standard deviation = 51.5 ± 8.0%) and Bacteroidetes (27.6 ± 6.7%); from these phyla, the most abundant orders were Rhodobacterales (21.8 ± 2.0%), Flavobacteriales (13.5 ± 9.4%), Chitinophagales (9.7 ± 1.8%), Alteromonadales (9.5 ± 4.0%), and Burkholderiales (3.8 ± 0.8%). Opportunistic pathogenic bacterial genera, such as Vibrio spp. and Pseudomonas spp., were detected at very low relative abundances (<1.2%), indicating that P. crassirostris nauplii could be considered a safe microbiological live feed. Furthermore, P. crassirostris nauplii were a good vector for probiotics delivery, as the adhesion of probiotics on the copepod exoskeleton was successful. Bacillus spp. abundance was 5–6× greater than the abundance of Lactobacillus spp. in P. crassirostris nauplii. The highest mean values of probiotics relative abundance (Bacillus spp. 41 ± 6.0%, Lactobacillus spp. 6.0 ± 3.0%) were observed in nauplii that were reared with probiotics and also enriched with probiotics. Conclusion: Parvocalanus crassirostris nauplii stages I–II appear to be good vectors to provide probiotics to first‐feeding fish larvae. Impact statementMarine fish aquaculture relies on quality live feed for optimal protein production. Assessing copepod nauplii's microbiological safety as fish larvae prey and their role as probiotics vectors is an important contribution to marine fish aquaculture. [ABSTRACT FROM AUTHOR]