Feces were sampled by siphonning the bottom of the fish tanks.  DNA was extracted using the QIamp¨ Fast DNA Stool Mini Kit from QIAGEN according to the manufacturer's instructions.  The DNA was amplified by PCR using the primers S-D-Arch-0519-a-S-15  (5ÕCAGCMGCCGCGGTAA-3' ) and S-D-Bact-0785-b-A-18 (5Õ-TACNVGGGTATCTAATCC-3Õ ) specific to region V4 of rRNA 16S. We used the TaKaRa Premixª 2.0 to perform the PCR according to the manufacturer's instructions. DNA concentration was quantified on Nanodrop. The sequencing was done on Illumina MiSeq.