Microbiota of the intestinal tract of salinity-tolerant Cyprinodon variegatus riverendi

Background: Cyprinodon variegatus riverendi is a small fish that can develop in different ecological niches. Furthermore, this species tolerates salinity and other stress factors that converge simultaneously. In the Dominican Republic, the Dunas Lagoon is a semi-enclosed ecosystem fringed by mangroves and halophytic vegetation, which sustains a diverse array of fish, crustaceans, insects, and algae. Two conduits connect it to Las Calderas Bay, allowing tidal seawater to enter. Meanwhile, low rainfall, a highly porous substrate, and intense insolation drive rapid water level declines ( 40 days) and salinity surges induced by evaporation that can exceed 200%. This type of fish can be found in these niches with a high salinity content. The ability of these animals is related not only to their specific cellular structural components but also to their intestinal microbiota. Results: The intestinal microbiota composition of Cyprinodon variegatus riverendi was described using a shotgun metagenomic approach, revealing the components of this system, including bacteria, archaea, viruses, and fungi. The diversity and composition analysis of the different microbial communities was presented, with a significant proportion of Serratia marcescens, Mycobacterium cariettii, Glutamicibacter sp., and Klebsiella pneumoniae. Some methanogenic species of archaea were found, as well as giant viruses and fungi. The functional genes stood out in the analyzes, with a predominance of metabolites that help fish tolerate stress and the presence of the Cetobacterium species, which has properties related to the production of protective metabolites. Conclusion: C. variegatus riverendi harbors a specialized, function-rich gut microbiome that likely augments host osmoregulation and oxidative stress resistance, enabling life in hypersaline niches. This community also represents a reservoir of extremotolerant microbes and enzymes with potential applications in aquaculture health management, bioremediation, and saline-process biotechnology.