Red sea bream iridovirus (RSIV) of the Iridoviridae family is a causative agent of lethal infections in many cultured marine fish species in southwestern Japan. RSIV-induced apoptosis was divided as follows: (1). cell shrinkage and rounding at the early apoptotic stage, (2). cell enlargement at the middle apoptotic stage, (3). formation of apoptotic body-like vesicles at the late apoptotic stage and phagocytosis by neighboring cells, and (4). loss of membrane integrity in apoptotic body-like vesicles without phagocytosis by neighboring cells. By affinity labeling, RSIV-induced apoptosis included caspase-dependent apoptosis. RSIV infection caused cell rounding but not cell enlargement or formation of apoptotic body-like vesicles and further restricted part of the structural protein synthesis in the presence of caspase-3 and -6 inhibitors. These findings showed the involvement of caspase-3 and -6 in the morphological changes at the middle and late apoptotic stages and viral protein synthesis in the late stage of RSIV infection.

Edwardsiella piscicida strains JF1307 and JF1411 were isolated from cultured olive flounder that were diagnosed as being infected with edwardsiellosis. The draft genome sequences of the two isolates comprise 3,882,000 bp and 3,827,424 bp with G+C contents of 59.5% and 59.6%, respectively.

In Japan, a Mycobacterium marinum-like mycobacterium was isolated from the yellowtail, Seriola quinqueradiata. The species was identified as M. marinum by a commercial mycobacterial DNA-DNA hybridization kit. Nevertheless, PCR restriction analysis of the DNA of its RNA polymerase β-subunit gene definitively showed that this Mycobacterium sp.

Objective Edwardsiella tarda has been regarded as the causative agent of edwardsiellosis in cultured marine and freshwater fish species in Japan. Our previous study genetically classified an E. tarda‐like isolate from diseased Olive Flounder Paralichthys olivaceus as E. piscicida and that from diseased Red Seabream Pagrus major as E. anguillarum. This study aimed to understand the phenotypic differences between E. piscicida and E. anguillarum. Methods Fourteen E. piscicida and seven E. anguillarum isolates were used in this study. The colonies of each isolate were grown on brain–heart infusion agar plates and then subjected to DNA extraction. The extracted DNA was amplified using PCR. carbohydrate fermentation of the isolates was examined using API 50 CH test kits. Moreover, the growth of the two species was examined in defined media. Also, free amino acids in Olive Flounder and Red Seabream sera were detected and quantified via high‐performance liquid chromatography–mass spectrometry. Statistical differences in the concentrations of free amino acids were analyzed using Welch's t‐tests. Result The API 50 CH test revealed that L‐arabinose and D‐mannitol were fermented by E. anguillarum isolates but not E. piscicida isolates. Furthermore, the growth of E. piscicida and E. anguillarum was reduced in the defined medium without methionine and iron sulfate. The growth of E. piscicida was reduced in the defined medium without phenylalanine, tyrosine, alanine, or nicotinic acid, whereas the growth of E. anguillarum was reduced in the defined medium without serine, cysteine, leucine, threonine, or isoleucine. Tyrosine and alanine were present in higher concentrations in the Olive Flounder serum, whereas threonine and isoleucine were present in higher concentrations in the Red Seabream serum, suggesting favorable growth conditions for E. piscicida and E. anguillarum. Conclusion This study characterizes a minimal defined medium that can be used for developing vaccines against E. piscicida and E. anguillarum.

Vibrio harveyi strain GAN1709 was isolated from a diseased greater amberjack farmed in Nomi Bay, Japan. Here, we report the draft genome sequence of this strain, which comprises 6,265,473 bp, with a G+C content of 44.8%.

An outer membrane protein (OMP) of the fish pathogenic bacterium Edwardsielia tarda was investigated on its antigenic property. Bacterial agglutination reaction and SDS-PAGE /westem blotting analysis using selected rabbit antisera demonstrated that a 37 kDa OMP was a common antigen among 17 E. tarda strains. Immunoelectron microscopy demonstrated that the 37 kDa OMP located on/in the outer membrane of the bacterium. Immunization of Japanese eel with the 37 kDa OMP prepared from two different serotype strains showed protection against intraperitoneal injection with one strain. Immunization of Japanese flounder with the 37 kDa OMP prepared from one strain also showed protection against injection with two different serotype strains. The results indicate that the 37 kDa OMP is a cell surface protective antigen commonly effective against different serotypes of E. tarda.