We identified and characterized full-length cDNAs of rock bream Oplegnathus fasciatus major histocompatibility complex (RbMHC) class I and β2-microglobulin (Rbβ2m) molecules. The full-length RbMHC class I cDNA was 2,667 bp with a 1,227 bp open reading frame encoding 409 amino acids (aa). The Rbβ2m full-length cDNA (1,339 bp) consisted of a 354 bp coding region, encoding 118 aa. RbMHC class Iα was clustered with the Z/ZE lineage of known MHC class I sequences, suggesting a novel molecule belonging to the Z/ZE lineage. Although characteristic features (residues and motifs) known to be conserved in classical and non-classical class I molecules were conserved in RbMHC class Iα with few modifications, it is more closely resembled to classical MHC class I. RbMHC class I and Rbβ2m were transcribed constitutively in healthy fish, but expression differed among the different organs and was highest in whole blood. Low sequence variation in the RbMHC class I α1 region makes it uncertain whether the molecule belongs to the non-classical group. However, because transcription was induced by megalocytivirus, the molecule is most likely a member of the classical group. Our results provide important information for future studies on antigen presentation and cytotoxic CD8+ T cell responses in rock bream against infectious pathogens.
Cyprinid herpesvirus 3 (CyHV-3), also called as koi herpesvirus, has spread all over the world since its emergence in the late 1990s. CyHV-3 causes a fatal disease, which leads to a mortality rate of more than 80% in common and ornamental (koi) carp Cyprinus carpio. The novel anti-CyHV-3 strategies are urgently needed. In this report, CyHV-3 particles were concentrated and then used for the immunization of hens in order to obtain the anti-CyHV-3 egg yolk immunoglobulin (IgY). The proportion of anti-CyHV-3 IgY to total IgY in water-soluble fraction of egg york increased from 0.014% to 23.9% after three times of immunization. The anti-CyHV-3 effects of IgY were then examined by in vivo and in vitro assays. The results suggested that the anti-CyHV-3 serum of hens and the purified anti-CyHV-3 IgY from eggs could prevent common carp brain (CCB) cells from infection. After oral passive immunization with IgY, the mortality of carp significantly decreased from 85% to 50% (P < 0.05) when the fish were challenged with CyHV-3 at a dose of 40 TCID50/fish. These results will possibly pave the way for the prevention of CyHV-3 infection.
Tenacibaculum maritimum is a Gram-negative, gliding marine bacterium that causes tenacibaculosis, an ulcerative disease of marine fish. The bacterium usually forms rhizoid colonies on agar media. We isolated T. maritimum that formed slightly yellowish round compact colonies together with the usual rhizoid colonies from a puffer fish Takifugu rubripes suffering from tenacibaculosis, and studied the biological and serological characteristics of a representative isolate of the compact colony phenotype, designated strain NUF1129. The strain was non-gliding and avirulent in Japanese flounder Paralichthys olivaceus in immersion challenge test and showed lower adhesion ability to glass wall in shaking broth culture and to the body surface of flounder. It lacked a cell-surface antigen commonly detected in gliding strains of the bacterium in gel immunodiffusion tests. SDS-PAGE analysis showed different polypeptide banding patterns between NUF1129 and gliding strains. Like gliding strains, NUF1129 exhibited both chondroitinase and gelatinase activities, which are potential virulence factors of the bacterium. These results suggest that some cell-surface components related to gliding and adhesion ability are implicated in the virulence of T. maritimum.
In the previous study, we evaluated the protective efficacies of the following three vaccines for the thread-sail filefish Stephanolepis cirrhifer: a commercial Streptococcus iniae vaccine, a commercial Lactococcus garvieae vaccine and a combination of these two vaccines. In this study, we examined the three vaccines for the thread-sail filefish in terms of protective duration, protection against various heterogeneous strains of S. iniae and L. garvieae, and the effects of different water temperatures on the protection. The vaccines induced strong protection against heterogeneous strains of S. iniae and L. garvieae, and the protection was observed for 52 weeks after the vaccination. These vaccines also induced protective immunity when administrated at 15°C, 20°C and 25°C.
The effect of elevated water temperature on the myxosporean emaciation disease caused by Enteromyxum leei was tested in experimentally infected anemonefish Amphiprion ocellaris and naturally infected Malabar grouper Epinephelus malabaricus. Anemonefish reared at 30°C following infection had significantly lower parasite prevalence compared to fish reared at 23°C. After infection in anemonefish held at 23°C for 20 days, elevation of water temperature to 30°C reduced the prevalence. Holding infected Malabar grouper at 30°C resulted in a clearing of E. leei within 6 days. Histopathological observations showed that E. leei was eliminated following exfoliation of the intestinal epithelial cells. Although further replication of the study would be required, these results suggested that high water temperature treatment had a preventive and therapeutic effect on myxosporean emaciation disease.
Kudoa infections have recently become a serious concern in Japanese fisheries. Some species not only cause fish diseases and reduce the commodity value of fish, but also affect human health. We investigated whether the ultraviolet (UV) treatment of culture water prevented infections with two species of Kudoa, K. yasunagai and K. amamiensis, in Seriola lalandi and S. quinqueradiata, respectively. Rearing in untreated filtered seawater resulted in high infection rates, suggesting that the physical filtration systems used in this study did not sufficiently remove the infective stages of these Kudoa species. In contrast, commercially available UV irradiation system effectively prevented the infections with K. yasunagai and K. amamiensis.