Previous typing of microsatellite markers in a BC1F1 backcross rainbow trout Oncorhynchus mykiss revealed two quantitative trait loci (QTL) with a significant impact on susceptibility to infectious pancreatic necrosis. In the present study, additional genetic markers were mapped using the same strain in order to increase QTL resolution. A total of 199 individuals were screened at 226 marker loci (106 microsatellites, 116 amplified fragment length polymorphism markers, classical major histocompatibility complex molecules [MHC class I, nonclassical MHC class I, MHC class II] and tyrosinase) and the QTL were determined by single-point and interval mappings. Seven QTL were distinguished in the linkage groups RT-11, 12, 17, 23, 26, 29 and 31, in addition to the two already known in RT-3 and 22. The major QTL were those in RT-3, 12 and 22; whereas the classical MHC class I locus Onmy-UBA and the MHC class II locus Onmy-DAB were not associated with any of the QTL, a nonclassical MHC class I region with Onmy-UCA, Onmy-UDA, and Onmy-UEA mapped to the major QTL on RT-3.
A mass mortality of cultured kuruma prawn Penaeus japonicus occurred in Kagoshima Prefecture in June, 2005. Affected prawns displayed a sluggish behavior or swimming on their side. The mean water temperature during the disease outbreak was 27°C. A black pigment-producing bacterium was isolated from the diseased prawns and was identified as Vibrio nigripulchritudo by bacteriological tests, 16S rDNA sequence analysis and DNA array for discrimination of Vibrio species. High pathogenicity of the isolated bacterium to healthy kuruma prawn was confirmed by intramuscular injection. This is the first report of V. nigripulchritudo infection in kuruma prawn.
Kabatana takedai (Microspora) is known as an enzootic pathogen of salmonids in limited water systems such as the Chitose River in Hokkaido, northern Japan. In this study, susceptibility to K. takedai was compared among masu salmon Oncorhynchus masou originating from the Chitose River, Shiribetsu River and Shari River, and rainbow trout O. mykiss from Shizuoka Prefecture, Japan. After exposure of fish to the Chitose River water, cysts of K. takedai in the heart and trunk muscle were examined by microscopy. Prevalence and intensity of infection were not considerably different among the three populations of masu salmon, whereas rainbow trout was more susceptible to K. takedai than masu salmon, particularly in the heart. A newly developed PCR test showed the higher percentage of fish with pre-cyst stage of K. takedai in the heart of rainbow trout than in masu salmon, suggesting that K. takedai established the cardiac infection at early stages more in rainbow trout than in masu salmon. A histopathological observation indicated that K. takedai infection in the heart caused granulomatous inflammation characterized by fibrinoid degeneration, but there was no difference in the progress of the inflammation between the two fish species.
Ayu Plecoglossus altivelis that survived from bacterial coldwater disease (BCWD) were reinfected with Flavobacterium psychrophilum. Artificial reinfection challenge showed that the survival rate of ayu recovered from BCWD was significantly higher (84%) than that of naive ayu (2%) or ayu immunized with FKC vaccine (18%).
Distribution of nervous necrosis virus in asymptomatically infected orange-spotted grouper Epinephelus coioides was determined by PCR assay in this study. Fourteen different tissues and organs were collected from apparently healthy groupers including seven individuals of broodstock and 17 juveniles with body weight ranging from 4 to 12 kg and from 2 to 9 g, respectively. No cytopathic effects were found in E-11 cells inoculated with filtrates of sample homogenates. However, all the broodstock and juveniles were positive by nested PCR test except for one juvenile. One hundred percent detection rate of the virus was obtained only from the brain.