Tropical gar (Atractosteus tropicus) is freshwater and estuarine fish, inhabiting the Earth since the Mesozoic era and undergoing limited physiological variation ever since. Besides its recognized cultural andscientific relevance, the species has seen remarkable growth in its economic impact due to pisciculture. In this study, we present the first report of the whole taxonomic composition of microbial communities in gut contents in juveniles and adults of A. tropicus, by sex and origin (wild and cultivated). For this study, 508 genera were identified, with the most and least abundant being Cetobacterium and Paludibacter, respectively. Fusobacteria, Proteobacteria, Firmicutes, and Bacteroidetes phyla are the core gut microbiome of A. tropicus juvenile and adult by sex and origin. Deinococcus-Thermus phylum sequence was only identified in wild-type males. In the phylogenetic trees reconstruction Lactococcus lactis strains CAU929 and CAU6600, Cp6 and CAU9951,Cetobacterium strain H69, Aeromonas hydrophila strain P5 and WR-5-3-2, Aeromonas sobria strain CP DC28 and Aeromonas hydrophila were identified, some of them with probiotic potential within the three dominant phyla in core gut microbiome in A. tropicus adults, especially in wild-type organisms. Myroides genus was recognized in microbiota gut of the cultivated juvenile A. tropicus. Nevertheless, Alpha diversity indicated that the highest gut microbiota abundance and richness is found in cultivated juvenile and wild-type adult A. tropicus female, rather than adult wild-type males and the least gut microbiota abundance and richness is found in a cultivated adult of A. tropicus for both sexes.

Tropical gar (Atractosteus tropicus), is freshwater and estuarine fish that has inhabited 17 the Earth since the Mesozoic era, undergoing limited physiological variation ever since. This 18 omnivorous fish is endemic to southern Mexico and part of Central America. Besides its 19 recognized cultural and scientific relevance, the species has seen remarkable growth in its 20 economic impact due to pisciculture. Previous studies have highlighted the role of microbial 21 communities in fish, particularly those in the gut microbiome, in maintaining their host 22 homeostasis or disease. In this study, we present the first report of the whole taxonomic 23 composition of microbial communities in gut contents of adults' A. tropicus, by sex (female/male) 24 and origin (wild/cultivated). Using culture-independent techniques, we extracted metagenomic 25 DNA that was used for high throughput 16S rDNA profiling by amplifying the V4 -V5 26 hypervariable regions of the bacterial gene. A total of 364,735 total paired-end reads were 27 obtained on an Illumina MiSeq sequencing platform, belonging to 508 identified genera, with the 28 most and least abundant are Cetobacterium, Edwardsiella, Serratia, Clostridium sensu stricto, 29Paludibacter and Campylobacter, Snodgrassella, Albirhodobacter, Lentilitoribacter, respectively. We 30 detected that, by sex and origin, Proteobacteria, Fusobacteria, Firmicutes and Bacteroidetes phyla 31 are the core gut microbiome of the adults' A. tropicus. We discover the Deinococcus-Thermus 32 phylum sequence, wildtype males only, with extremophile capacity in another freshwater fish. 33We also identified the species Lactococcus lactis strains CAU929 and CAU6600, Cp6 and CAU9951, 34Cetobacterium strain H69, Aeromonas hydrophila strains P5 and WR-5-3-2, Aeromonas sobria strain 35 CP DC28 and Aeromonas hydrophila with probiotic potential in aquaculture within the three 36 dominant phyla, especially in wild-type organisms. 37