We determined the identity of an aporocotylid blood fluke discovered in the gills of southern bluefin tuna Thunnus maccoyii ranched in Australia. Both morphological and molecular data indicate the parasite is Cardicola orientalis, reported previously only from Pacific bluefin tuna T. orientalis in Japan. Over 70 C. orientalis adults were retrieved from a single gill arch of an infected southern bluefin tuna and numerous eggs were observed in the gill filaments suggesting possible pathology to the host. In addition, we obtained new information on morphological characteristics and molecular sequences of C. forsteri infecting the heart of T. maccoyii. This is the first report of C. orientalis in T. maccoyii, which may have a significant impact on the ranching industry of southern bluefin tuna and warrants further investigation.
The aim of this study was to look for new potential probiotic bacterial strains for marine aquaculture. Only one of 195 isolates from the gut of cultured fish including sea bass Dicentrarchus labrax, gilthead sea bream Sparus aurata, meagre Argyrosomus regius and sole Solea solea showed a strong inhibitory effect against Vibrio anguillarum. This isolate, identified as Enterococcus gallinarum, also produced a moderated protective effect against V. anguillarum infection of sea bass. Intraperitoneal injection with the isolate showed no pathogenicity in sea bass. Thus, the isolate designated E. gallinarum L1 can have a potential of probiotic bacterium.
We evaluated the effects of temperature and salinity on in vitro trophozoite proliferation and zoosporangial development in Perkinsus olseni and P. honshuensis, infecting Manila clam. Trophozoite proliferation was highest at 28°C for both species and at 18-21‰ and 21-33‰ for P. olseni and P. honshuensis, respectively. Zoospore release rates, as the indicator of zoosporulation, were highest at 25-30°C and 25-35‰ for both species. However, these results seem not to explain the previously observed phenomena, i.e. lower infection prevalence in estuarine tidal flats (the two species not distinguished) and higher infection prevalence of P. olseni than P. honshuensis.
We investigated virulence and elastin-degrading activity in ten strains of Flavobacterium psychrophilum isolated from chum salmon Oncorhynchus keta in Hokkaido, Japan through 2004 to 2006. Intraperitoneal injection of these strains to chum salmon fry revealed that 50% lethal doses (LD50) of the strains were from 2.6 × 105 to 4.7 × 107 CFU/g. No clear relationship between elastin-degrading activity and virulence in these strains was found. These results indicate that the virulence of F. psychrophilum isolated from chum salmon varies considerably among strains, and is not clearly related to elastin-degrading activity.
We optimized the quantitative detection of red seabream iridovirus (RSIV) genome from splenic tissues of rock bream Oplegnathus fasciatus using the quantitative polymerase chain reaction assay targeting the Pst I fragment gene. The regression line for quantitative detection of the RSIV genome was y = -0.266x + 10.95 (amplification efficacy: 84.5%), which was available between Ct 8 and 33. The quantitative-detection limit of the assay was 103.5 genomes/mg. The RSIV genome was under the quantitative-detection limit in fish by day 7 of RSIV inoculation, whereas ≥ 106.71±1.77 genomes/mg (mean ± SD) of RSIV were detected in fish from 10 days after RSIV inoculation.
Juvenile greater amberjack were placed in a small cage and exposed to Neobenedenia girellae oncomiracidia for 48 h at an amberjack culture site under natural light or with a shade. The shading reduced worm intensity on the skin of fish by about 70%. Additional laboratory experimental infection comparing the larval infectivity under dark and light conditions revealed that the oncomiracidia were capable of infecting fish in complete darkness. These results suggest that the low infection rate in the shaded water is probably due to accumulation of the oncomiracidia into the bright area, resulting in the lowered density under the shade.