Raw reads
The fish intestine DNA without feces was extracted using a DNAeasy blood & tissue kit (Qiagen, USA) according to the manufacturers instructions. The DNA in water samples was extracted from 0.45 m filters using a Quiamp Fast DNA Stool (Qiagen, USA) kit according to the manufacturers instructions. The DNA concentration was measured with a Nanodrop spectrophotometer. Three water samples per site and three intestine fish samples per condition were pooled in a final 100 ng/L concentration.  The full 16S rRNA gene was amplified using the primers 27 F 5-AGAGTTTGATCCTGGCTCAG-3 and 1492 R 5-GGTTACCTTGTTACGACTT-3 [26]. Taq DNA polymerase LongAmp (NewEngland Biolabs, USA), with a volume reaction of 15 L, was used for amplification under the following conditions: 95 C for 1 min, followed by 30 cycles of 95 C for 20 sec, 56 C for 30 sec, and 65 C for 1 min, ending with a final extension at 65 C for 5 min The effectiveness of the PCR was evaluated using 1% agarose gel electrophoresis.