Metagenomic signatures of transportation stress in the early life stages of cobia (Rachycentron canadum) to aid in mitigation strategies

Cobia (Rachycentron canadum) is a high-value marine aquaculture species. Knowledge of the microbial dynamics in various aquaculture operations is crucial for developing suitable management practices. The present study revealed the critical dysbiotic events in the whole larval and juvenile-gut microbiome of cobia, through an inevitable aquaculture operation, viz. live transportation. The results through both culture-dependent and independent techniques demonstrated the sensitivity of the cobia microbiome during early life, where live transport is inevitable. In detail, there was a significant change in the microbial composition and reduction in the cultivable load of all the life stages. Further, a significant reduction in functional metagenomics along with an increase in taxonomic metagenomics was recorded in the L21 stage. Significant reductions of the putative healthy microbiota, viz., Proteobacteria and Actinobacteria were remarkable in the whole larval microbiome. The analysis through linear discriminant analysis effect size revealed that the opportunistic fish pathogens, viz., Vibrio spp., Arcobacter spp., and Acinetobacter spp. were increased whereas, Pseudomonas spp. was decreased in larvae following transportation. The significant reduction in the taxonomic diversity measures was noteworthy in the juvenile-gut microbiome. Transportation promoted Serratia spp., Enterobacter spp., an unidentified genus in Flavobacteriaceae, Pseudoalteromonas spp., Alteromonas spp., and Enterovibrio spp., and inhibited Empedobacter spp. in the juvenile gut. Collectively, the results provide the prospective metagenomic signatures of health and stress in the early life stages of cobia and novel possible explanations for increased disease susceptibility post transportation. The study warrants future research on the microbes which were found to be decreased following transportation, as potential probiotics to mitigate the stress in the marine aquaculture practices. The metagenomic signatures revealed through the study can be further applied for evaluating different husbandry practices to mitigate stress during live transportation.