design: Three commonly used primer pairs were utilized in this study, AcMDB07-F and AcMDB07-R for the fish 12S rRNA gene, Uni18S and Uni18SR for the eu-karyotic hypervariable V4 region of the 18S rRNA gene, and TAReuk454FWD1 and TAReukREV3 for the eukaryotic hypervariable V4 region of the 18S rRNA gene.