design: Total genome DNA was extracted from all samples using the FastLee DNA kit for Feces (Hangzhou Legenomics Bio-Pharm Technology Co., Ltd., China according to the manufacturer's instructions. The bacterial communities in the rearing water and intestine were characterized by high-throughput sequencing of the V4V5 hypervariable region of the 16S rRNA gene. Amplification was performed using the universal primer pair 515F (5-GTGCCAGCMGCCGCGG-3) and 907R (5-CCGTCAATTCMTTTRAGTTT-3). PCR reactions were performed in a 30 L volume with 15L of PhusionHigh-Fidelity PCR Master Mix (New England Biolabs); 0.2 M of forward and reverse primers, and approximately 10 ng template DNA. The thermal cycling protocol consisted of an initial denaturation at 98 for 1 min, followed by 30 cycles of denaturation at 98 for 10 s, annealing at 50 for 30 s, and extension at 72 for 60 s, with final exension at 72 for 5 min. PCR products were combined with an equal volume of loading buffer and analyzed by electrophoresis on 2% agarose gel. Products displaying a bright primary band between 400-450 bp were selected for subsequent steps. Equimolar amounts of PCR products were pooled and purified using the GeneJET Gel Extraction Kit (Thermo Scientific). Sequencing libraries were constructed with the NEB NextUltraDNA Library Prep Kit for Illumina (NEB, USA) following the manufacturers protocol, and index codes were added. Library quality was assessed on the Qubit@ 2.0 Fluorometer (Thermo Scientific) and Agilent Bioanalyzer 2100 system. The libraries were then sequenced on an Illumina MiSeq platform to generate 250 bp/327 bp paired-end reads.