Temporal fluctuation in the abundance of alginate‐degrading bacteria in the gut of abalone Haliotis gigantea over 1 year

In this study, we identified and enumerated alginate‐degrading bacteria in the gut of abalone over 1‐year period. From a total of 360 colonies growing on agar medium enriched with alginate, 251 isolates (70%) had the ability to degrade alginate. In addition, a high number of viable alginate‐degrading bacteria were detected throughout the survey period. Alginate‐degrading bacteria were more abundant in the cold season relative to the summer season (10⁷ vs. 10⁴ CFU g^?1, respectively). Strong positive correlation was also observed between the number of alginate‐degrading bacteria and feed intake (R = 0.854; P < 0.01). The identified alginate‐degrading bacteria comprised of 35 species grouped into 11 genera including Algibacter, Formosa, Polarybacter, Tamlana, Tenacibaculum (CFB group), Roseobacter, Ruegeria, Silicibacter (α‐proteobacteria), Agarivorans, Shewanella and Vibrio (γ‐proteobacteria) respectively. More than 80% of the isolated alginate‐degrading bacteria belonged to the genus Vibrio, showing high homology to Vibrio cyclotorophicus, Vibrio splendidus, Vibrio halioticoli and Vibrio neonatus. Based on the results, it was suggested that algal‐polysaccharide (alginate) degrading bacteria (mainly Vibrio) commonly exist in the gut of abalone and may play an important role in the degradation and digestion of the host's feed.     

Establishment of a model for chemoattraction of <Emphasis Type="Italic">Symbiodinium</Emphasis> and characterization of chemotactic compounds in <Emphasis Type="Italic">Acropora tenuis</Emphasis>

Corals harbor symbiotic dinoflagellates, Symbiodinium spp., acquired from surrounding environments. Because Symbiodinium are present at low densities in the water column, corals may attract these symbionts using chemotactic compounds. To examine whether corals contain chemotactic compounds, we established an assay to measure the chemotactic activity for Symbiodinium using an extract of the coral Acropora tenuis, a major reef-building coral in Japan. Our assay revealed that Symbiodinium strain NBRC102920 (clade A), which is taken up by juvenile A. tenuis polyps, is attracted to crude A. tenuis extracts. We found that the chemotactic compounds are water-soluble, heat-labile macromolecules and that the chemotactic activity was inhibited by N-acetyl-d-glucosamine (GlcNAc). We separated the GlcNAc-binding fraction (Fr-ActL) and identified it as the most plausible candidate for the chemoattractant, since the chemotactic activity of the crude A. tenuis extract appeared to be mainly attributable to the activity of Fr-ActL and was also inhibited by the addition of GlcNAc. These results indicate that chemoattraction is mediated via the binding of Symbiodinium to Fr-ActL.     

Susceptibility of isogeneic ginbuna Carassius auratus langsdorfii Temminck et Schlegel to cyprinid herpesvirus‐2 (CyHV‐2) as a model species

Herpesviral haematopoietic necrosis (HVHN), caused by cyprinid herpesvirus‐2 (CyHV‐2), has affected the commercial production of the goldfish Carassius auratus and gibelio carp Carassius auratus gibelio. High water temperature treatments are reported to reduce the mortality rate of infected goldfish and elicit immunity in the survivors. To define the mechanism by which this intervention induces resistance, clonal ginbuna Carassius auratus langsdorfii, which is closely related to both species and has been used in fish immunology, may represent a promising model species. In this study, we investigated the susceptibility of clonal ginbuna strains to CyHV‐2 and the effect of high water temperature treatment on infected ginbuna and goldfish. Experimental intraperitoneal infection with CyHV‐2 at 25 °C caused 100% mortality in ginbuna strains, which was accompanied by histopathological changes typical of HVHN. Both infected ginbuna S3n strain and goldfish, exposed to high temperature for 6 days [shifting from 25 °C (permissive) to 34 °C (non‐permissive)], showed reduced mortalities after the 1st inoculation, and subsequent 2nd virus challenge to 0%, indicating induction of immunity. It was concluded that ginbuna showed a similar susceptibility and disease development in CyHV‐2 infection compared to goldfish, suggesting that ginbuna can be a useful fish model for the study of CyHV‐2 infection and immunity.     

A preliminary experiment regarding the natural induction of gonadal development in female Japanese eels without hormone treatment

To test whether gonadal development of female eels could be promoted without any exogenous hormone treatments, we observed the effect of water temperature manipulation. After 3–5 months of water temperature treatments, three silver eels showed higher gonadosomatic indices (GSI). In particular, one eel in the 5–15°C fluctuating temperature treatment group (5°C daytime and 15°C night‐time) had the highest GSI of 8.5 with secondary yolk globule stage oocytes of large diameter (OD; 412 μm) after 3 months, which indicated definite gonadal development compared with those in the initial states (mean GSI, 2.4; OD, 226.7 μm). The 5–15°C fluctuating temperature and constant 5°C groups had low oocyte breakdown (atretic) rates. Because daily temperature fluctuations and cold daytime water are experienced by vertically migrating silver eels in the ocean, these temperature conditions may be key maturation process components that could be useful for hormone‐free artificial maturation.     

Isolation and characterization of bacteria causing mortality in early stage larvae of captive‐bred Japanese eels (Anguilla japonica Temminck & Schlegel)

Bacteria with lethal effect on eel larvae were isolated from moribund captive‐bred eel larvae and their 16S rRNA gene sequences were analysed. Nucleotide sequence of 10 isolates showed highest similarity with Lacinutrix algicola, Crocinitomix catalasitica and Pseudoalteromonas rubra. Age‐dependent changes in the susceptibility of eel larvae were observed in response to challenge by a highly lethal isolate. Compared with 10 and 11 days after hatching (DAH), larval susceptibility to the highly lethal isolate was lower at 18 DAH. We found that the bacterial isolates have lethal effect on the captive‐bred eel larvae, especially at the early developmental stage. These results will be useful to establish appropriate culture practices for eel larvae that will improve the success of mass production of glass eels for aquaculture.     

Mutation induction with ion beam irradiation of lateral buds of chrysanthemum and analysis of chimeric structure of induced mutants

We compared the effects of ion beam and gamma ray irradiation on mutation induction in axillary buds of chrysanthemum, and analyzed the chimeric structure of the resulting mutants. Axillary buds were irradiated with carbon ions at 2 Gy (mean linear energy transfer 122 keV/μm), helium ions at 10 Gy (mean 9 keV/μm), and gamma rays at 80 Gy, all of which have the similar effects on survival. The lower five nodes of the shoots elongating from the irradiated buds were cut one by one, and new shoots were allowed to grow from the axillary buds. This procedure was repeated twice, and flower color mutation was investigated. Chimeric structure was analyzed by comparing the flower color of mutants to that of plants regenerated from the roots. Flower color mutants emerged at a high frequency (17.4–28.8%), and there were no significant differences in the mutation frequency between the treatments. All the flower color mutants induced with gamma rays were periclinal chimeras. In contrast, some mutants obtained with ion beams had the same flower color as that of the plants derived from the roots. This suggests that they were solid mutants, where both LI and LIII tissues were derived from the same mutated cell. Solid mutants were also obtained when irradiated with 5 Gy of helium ions, which had less effect on survival and mutation than other treatments. Factors for obtaining solid mutants only with ion beams are also discussed.     

Comparison of right atrium incision and right ventricular outflow incision for surgical repair of membranous ventricular septal defect using cardiopulmonary bypass in dogs

OBJECTIVE: To compare right atrium incision (RAI) and right ventricular outflow incisions (RVI) for surgical repair of membranous ventricular septal defect (VSD) facilitated by cardiopulmonary bypass (CPB). STUDY DESIGN: Retrospective study. ANIMALS: Dogs (n=10) with VSD. METHODS: Medical records of dogs that had VSD repair were reviewed. Membranous VSD without any malformation and abnormality was confirmed on several clinical examinations and by angiocardiography. RAI (5 dogs) and RVI (5 dogs) was used for VSD access and repair facilitated by CPB. Procedure comparison was by surgical duration, postoperative recovery period, and occurrence of postoperative arrhythmia. RESULTS: Duration of surgery was similar for RAI and RVI; however, postoperative recovery time was significantly reduced with RAI. Significant moderate operative damage occurred with right atrium incision. CONCLUSIONS: Right atrium incision was more effective than RVI for repair of membranous VSD using CPB. CLINICAL RELEVANCE: RAI should be considered in preference to RVI for repair of membranous VSD using CPB.