Characterization of the goldfish fecal microflora by the fluorescent in situ hybridization method

ABSTRACT:   Bacterial populations in goldfish feces were characterized by the fluorescent in situ hybridization (FISH) method. A total of nine different group-specific rRNA-targeted oligonucleotide probes were used. Approximately half of the microbial cells (57.8 ± 16.7%) were detected with a probe EUB338 and found to be bacteria. The microbial cells in 33–35 of the 35 samples from five specimens strongly hybridized with probes ALF1b, BET42a and GAM42a, suggesting that goldfish intestinal bacteria are mainly composed of α, β and γ-subclasses of Proteobacteria. The fact that a probe AER66 reacted with 25.6 ± 14.2% of the total microbial cells in all 35 samples, demonstrated that genus Aeromonas was the dominant species in the goldfish intestines. Genus Bacteroides including Bacteroides type A detected with a probe BAC303 was observed in 15 of 35 samples while other taxonomic groups determined with HGC69a, CF39a and P72 were detected in 6–11 of 35 samples. These results strongly suggest that Bacteroides shows the greatest daily fluctuation and interindividual variation in the intestines of goldfish. Moreover, the FISH method was proven to be useful for rapid enumeration of taxonomic groups of fish intestinal bacteria.