Results of long-term investigation of infection prevalence of fish eggs and larvae with the endoparasite Ichthyodinium sp. (Dinoflagellata) in Nha Trang Bay (South China Sea, Vietnam) are presented. The parasite was identified on the base of morphological characteristics and phylogenetic analysis with 18S rRNA sequences. After the first record in 1993 the infection rate steadily increased till 2004, remainded high in 2004-2007, decreased in 2008-2009 and again boosted in 2010. Seasonal and annual dynamics of the infection rate was described. The parasite showed different degrees of prevalence in different taxonomic groups of fishes. The infection rates were different among closely related species. This is the first report on long-term dynamics of Ichthyodinium infection in Southeast Asia.
Acremonium sp. NJM 0672, isolated from diseased mantis shrimp Oratosquilla oratoria, was susceptible in vitro to three kinds of antifungal agents: voriconazole, amphotericin B and terbinafine hydrochloride. Voriconazole was selected to treat kuruma prawn Penaeus japonicus, which had been intramuscularly injected with 0.1 mL of 5.0 × 104 conidia/mL of Acremonium sp. Voriconazole was administered orally at doses of 6 and 2 mg/kg body weight per day for 7 consecutive days, or intramuscularly injected at doses of 4 and 2 mg/kg body weight per day for 3 consecutive days. Both treatments were begun at 6 h after injection of the conidial suspension. The gross features, mortality and histopathological findings demonstrated that voriconazole was an efficient antifungal agent against Acremonium sp.
Occurrences of bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum were monitored among released and wild ayu Plecoglossus altivelis in Hirose River in 2006 and 2007 in order to clarify the infection source. When hatchery-reared juvenile ayu were examined immediately prior to release, F. psychrophilum was not isolated. However, when fish from the same lots were reared until maturation, the bacterium was isolated from ripe fish, indicating that the released juvenile ayu were carriers. In epizootiological investigations in Hirose River, outbreaks of BCWD occurred from June to August in both years, but the source of BCWD seemed to differ: released ayu in 2006 and wild ayu in 2007. Additionally, the disease occurred in released ayu by the pathogen carried by themselves in 2007. The disease subsided in August when water temperature exceeded 20°C. Thereafter, the prevalence of F. psychrophilum in ripe fish in the river increased to above 90% between October and November in both years.
The role of leukocytes from the kidney of Japanese flounder Paralichthys olivaceus in the encapsulation response was investigated using an in vitro model. The aggregation response of leukocytes to the target fish pathogen Ichthyophonus hoferi was observed over 12 h. The cellular aggregates mainly comprised granulocytes, which were characterized by intracellular peroxidase expression. Moreover, studies of isolated granulocytes demonstrated their adhesion to I. hoferi and formation of an initial layer in the encapsulation response. We observed that mRNA expression levels of three CC-chemokines (CCL3, CCL4 and CC-CLM) and one CXC-chemokine (IL-8) increased during the encapsulation process. Among these chemokines, CC-CLM and IL-8 were actively produced by granulocytes upon stimulation by I. hoferi. Flounder granulocytes therefore appeared to play an important role in the process by releasing specific chemokines upon pathogen recognition, thereby inducing subsequent cellular recruitment leading to encapsulation.
We designed a PCR primer set for specific detection of Miamiensis avidus causing scuticociliatosis in Japanese flounder Paralichthys olivaceus. In the PCR targeting the small subunit ribosomal RNA gene of M. avidus, the expected PCR product with 1,433 bp was amplified from four isolates of M. avidus including three different serotypes, but not from other scuticociliates including Pseudocohnilembus persalinus, P. hargisi and Uronema marinum. Detection limit of the present PCR was 125 fg of genomic DNA. When a group of Japanese flounder suffering the disease was examined by the PCR, 90% of symptomatic fish and 50% of asymptomatic fish were found positive. Thus it is considered that the PCR is useful for detection and identification of M. avidus and consequently for diagnosis of scuticociliatosis in Japanese flounder.
This study was carried out to assess the pathogenicity of Plectosporium oratosquillae NJM 0662 and Acremonium sp. NJM 0672, both of which were isolated from mantis shrimp Oratosquilla oratoris, to kuruma prawn Penaeus japonicus by intramuscular injection of conidial suspensions. These fungi caused mortality in the injected kuruma prawn. The diseased kuruma prawn showed numerous black spots in the gills. Histopathologically, hyphae in the gill filaments and the injected sites were encapsulated by hemocytes. The results indicate that these two fungi are pathogenic against kuruma prawn.
In 2005 and 2008, renal nephroblastomas were diagnosed in two adult male Siamese fighting fish Betta splendens. In both cases the masses effaced approximately 90 percent of renal tissue and histopathologically, were composed of a triptych of diagnostic features, to include: nests of cells suggestive of blastema, a primitive mesenchyme as well as an epithelial component forming glomeruloid structures. To our knowledge, these cases represent the first reports of nephroblastoma in Siamese fighting fish.
Detection of Piscirickettsia salmonis by the PCR targeting 16S rDNA has been applied to the diagnosis for piscirickettsiosis. However, some nucleotide substitutions were observed in the primer regions of the published PCR among several strains of P. salmonis. Thus, we designed a new PCR primer set targeting the 16S rDNA regions and a modified PCR program. The predicted amplicon was specifically generated from P. salmonis but not from 19 other bacterial species. Sensitivity of the present PCR system was also improved. It was confirmed that P. salmonis was detectable in the kidney and liver of the experimentally infected coho salmon Oncorhynchus kisutch by the present system.
One thousand forty-nine bacterial isolates, which were collected from shrimp farms in Thailand, were resistant to antimicrobial agents: ampicillin (ABPC), chloramphenicol (CP), kanamycin (KM), oxolinic acid (OA), streptomycin (SM) and tetracycline (TC). One hundred forty-two isolates were identified as Vibrio. These isolates were conjugated with Escherichia coli for detection of transferable R plasmid. Six patterns of transferable R plasmids, which encoded resistance to the combinations of one to five drugs (ABPC, CP, SM, sulfamonomethoxine, TC and trimethoprim), were found from 16 drug-resistant isolates of Vibrio. This is the first report of transferable R plasmids from Vibrio spp. in shrimp farms in Thailand.