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.
A total of 1347 bacteria isolated from environments and intestinal tracts of Japanese flounder, Paralichthys olivaceus, along with feeds, were examined for the antibacterial activity against four ...fish pathogens. As a result, 142, 22, 20 and 17 isolates inhibited the growth of P. piscicida K-III, V. vulnificus RIMD 2219009, E. seriolicida ATCC 49156 and V. anguillarum ATCC 19264, respectively, and 8.3-30.9% of isolates belonging to Aeromonas, Bacillus, coryneforms, Pseudomonas, Streptococcus and Vibrio showed activities against one of the four target bacteria. Antibacterial producers were detected at low densities and occurrence in rearing water, bottom sands and feeds, while those accounted for 59% of vibrios isolated from fish intestines. This result strongly suggests that antibacterial producers could not control fish pathogen efficiently in aquaria of Japanese flounder.
A total of 780 vibrios were isolated from Japanese flounder, Paralichthys olivaceus, at different stages of development and examined for the proteaseproducing ability of each isolate. The highest and ...lowest values in mean enzyme activities of isolates were observed on days 109 and 67 after hatching, respectively. High abilities (≥1.00U/μg) were detected in the isolates from fish on days 3, 23 and 45 after hatching, while as many as 62% of all vibrios showed low potential of production (<0.10U/μg). Inhibitory effects of PMSF and OPA were found in 61 and 50% of all Vibrio isolates, respectively. These results showed that larvae and juveniles of Japanese flounder harbor the vibrios capable of producing various types of proteases at different activities, in their intestines.
Antibacterial abilities of bacteria were determined for a better understanding of the role of intestinal microflora in coastal fish. Intestinal bacteria were isolated from five of each following ...species: horse mackerel, Trachurus japonicus, spotnape ponyfish, Leiognathus nuchalis, and red barracuda, Sphyraena pinguis, collected at Enoshima Island, Kanagawa. In the intestinal contents of three coastal fishes, genus Vibrio was the dominant bacterium and accounted for 5-100% of total viable counts ranging from 1.2×104 to 1.3×107 CFU/g. A total of 681 bacteria isolated from the water, sand and fish intestines were examined for their antibacterial abilities against four fish pathogenic bacteria, using the double layer method. Antibacterial producers were accounted for 15.0% of total isolates against Pasteurella piscicida K-III, 1.0% against Enterococcus seniolicida ATCC 49156 and 0.3% against both Vibrio anguillarum ATCC 19264 and Vibrio vulnificus RIMD 2219009. This result reveals that P. piscicida K-III may be much more susceptible than the other three fish pathogens. The growth of P. piscicida K-III was inhibited by 85 isolates of Vibrio spp., six of Acinetobacter spp., four of coryneforms and two of Bacillus spp. These results suggest that an indigenous antibacterial microflora may involve the protection of host fish against pathogenic bacteria to some extent.
