Supp file 1: The identity and abundance of KO terms enriched in isolate genomes that represent genera identified as being discriminatory of a given age class (organized by sheet). The log(10) LDA score for a KO term's abundance in discriminatory isolate genomes as compared to non-discriminatory isolate genomes is also given. Supp Table 1: Sample metadata for 16S rRNA gene sequencing samples and associated environmental measurements where applicable. Supp table 2: Primers used in this study. Supp Table 3: Identity and taxonomic placement of 26 zebrafish isolated strains used in this study. Supp Table 4: LDA scores of all taxonomic groups identified as discriminatory of zebrafish age classes. Supplementary Dataset 1: Abundance of OTUs and relative abundances of all taxonomic groups in fish and environmental samples summarized at all taxonomic levels from individual OTUs to phyla. A file for fish samples and a file for environmental samples is provided. Supplementary Information: Extended materials & methods and PICRUSt predicted metagenome results.