Changes in intracellular polyamine concentration during growth of Heterosigma akashiwo (Raphidophyceae)

ABSTRACT:   Of the free, conjugated and bound forms of polyamines, the free form of spermidine was the most abundant polyamine in Heterosigma akashiwo throughout the growth period except for the lag phase. Free spermidine content increased remarkably during the exponential growth phase and increased as the growth rate increased. The maximum growth yield of H. akashiwo was reduced by the addition of methylglyoxal bis-guanylhydrazone (MGBG) and the reduced growth yield could be counteracted by the addition of spermidine to the medium. It is concluded that spermidine plays a significant role in the growth of H. akashiwo . These results are similar to those obtained in Chattonella antiqua that belongs to same taxonomic Class as H. akashiwo .     

Annual dynamics of marine birnavirus (MABV) in cultured Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> and sea water

ABSTRACT:   Seasonal changes in the infection state of marine birnavirus (MABV) in Japanese flounder Paralichthys olivaceus and in rearing sea water are described. Sea water and 10–11 healthy fish were sampled monthly from April 2002 to February 2003. The MABV genome was detected throughout the year in > 80% of the fish examined at each sampling. The virus was isolated from the liver, kidney, and spleen, but not from the brain. The detection rate in each organ increased from April to October, and then decreased. Detection of virus antigen by the indirect fluorescent antibody technique also showed that the virus was present from spring to autumn (June–September) in the liver, kidney, and spleen, but not the brain. Sequence analysis of the MABV genome at the VP2–NS region revealed two specific mutations compared to the standard yellowtail strain (Y-6). It is suggested that the infection state of MABV in Japanese flounder changes to a latent or persistent infection after autumn. MABV was detected in sea water between September and February, suggesting that virus particles in the environment are relatively higher during cool seasons.     

Identification of juvenile abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis> based on number of open and sealed respiratory pores

ABSTRACT:   Changes in the number of respiratory pores (open pores) and their imprints (sealed pores) in post-larvae and juveniles were observed and compared for four abalone species Haliotis diversicolor , H. discus discus , H. madaka , and H. gigantea . The first open pore was evident at a shell length (SL) of 1.5 mm in H. diversicolor , 1.9–2.0 mm SL in H. discus discus , and 2.3–2.4 mm SL in H. madaka and H. gigantea . The number of open pores in H. diversicolor gradually increased with growth, with four to five pores at 2.5–18.0 mm SL and five to six pores at 18.0–27.0 mm SL. The other three species maintained four to five open pores after they reached 3.4–4.5 mm SL. The total number of open and sealed pores (TNP) was greater in H. diversicolor than in the other species at the same SL. Juvenile H. diversicolor were identified among field-caught abalone by the difference in the relationship between SL and TNP (SL–TNP relationship) and also by the monoclonal antibody reaction method. The results of the two methods were in perfect agreement, indicating that our method using the SL–TNP relationship is reliable for the identification of H. diversicolor .     

Assessing the population transmission dynamics of tilapia lake virus in farmed tilapia

A novel virus, tilapia lake virus (TiLV), has been identified as a key pathogen responsible for disease outbreak and mass mortality of farmed tilapia. We used a deterministic susceptible‐infectious‐mortality (SIM) model to derive key disease information appraised with published TiLV‐induced cumulative mortality data. The relationship between tilapia mortality and TiLV exposure dosages was described by the Hill model. Furthermore, a disease control model was proposed to determine the status of controlled TiLV infection using a parsimonious control reproduction number (R_C)‐control line criterion. Results showed that the key disease determinants of transmission rate and basic reproduction number (R₀) could be derived. The median R₀ estimate was 2.59 in a cohabitation setting with 2.6 × 10⁵ TCID50 fish^?1 TiLV. The present R_C‐control model can be employed to determine whether TiLV containment is feasible in an outbreak farm by quantifying the current level of transmission. The SIM model can then be applied to predict what additional control is required to manage R_C < 1. We offer valuable tools for aquaculture engineers and public health scientists the mechanistic‐based assessment that allows a more rigorous evaluation of different control strategies to reduce waterborne diseases in aquaculture farming systems.     

Molecular identification of red tide-causing microalga Heterosigma akashiwo strains based on their chloroplast DNA sequences

ABSTRACT:   In order to establish genetic signatures for intraspecific identification, parts of the genes rbcL , rbcS and psbA and their intergenic spacer (IGS) regions were amplified by polymerase chain reaction (PCR) from the chloroplast genomes of Heterosigma akashiwo strains isolated from Japan. A transfer RNA-Leu gene trnL and a hypothetical gene cfxQ , which is related to ribulose bisphosphate carboxylase/oxygenase expression, were found in the upstream region of the rbcL gene and in the rbcS-psbA IGS region, respectively. All the gene-coding regions and the IGS regions between rbcL and rbcS showed the same sequences among the strains tested. In contrast, the rbcL upstream regions and the rbcS-cfxQ IGS regions showed some differences such as nucleotide substitutions, duplications and inversions between NIES-5 and the other strains. Based on these sequence data, five genetic signatures were established and their simple and rapid detection by means of strain-specific PCR primers and PCR-restriction fragment length polymorphism techniques was examined. The results suggested the usefulness of these genetic signatures and techniques for the discrimination of H. akashiwo populations.     

Hexamitiasis leads to lower metabolic rates in rainbow trout Oncorhynchus mykiss (Walbaum) juveniles

This study assessed the effects of Hexamita salmonis (Moore) on metabolism of rainbow trout Oncorhynchus mykiss (Walbaum) and its effect on the host's susceptibility to infectious pancreatic necrosis virus (IPNV) after antiparasitic treatment. Rainbow trout naturally infected with H. salmonis were treated with 10 mg metronidazole kg fish^?1 per day, and their physiological recovery was assessed through measuring resting metabolism on the 7th, 14th, 21st and 28th day after treatment. In addition, we exposed the naïve fish to H. salmonis and measured the resting metabolism (oxygen consumption as mg O₂ kg^?1 per hour) on the 10th, 20th and 30th day after the exposure to assess the variation in metabolic rates after infection. Significantly lower rates of metabolic activity (P < 0.05) were anticipated 20 days after infection with H. salmonis compared with the fish infected with H. salmonis for 10 days or with the parasite‐free fish. Similarly, the treated fish needed about 20 days to fully recover from hexamitiasis. The susceptibility of rainbow trout to IPNV remained unchanged in the presence of H. salmonis. Weight loss was significantly higher (P < 0.05) in infected than that in the parasite‐free fish. Fish should be examined regularly for H. salmonis and treated immediately whether found to prevent economic losses and excessive size variation.     

Determination of the quality parameters of pike perch <Emphasis Type="Italic">Sander lucioperca</Emphasis> caught by gillnet,longline and harpoon in Turkey

ABSTRACT:   The effects of the different catching methods (gillnet, longline, harpoon) on sensory, chemical (pH, total volatile base nitrogen, K -value) and microbiological (total viable count [TVC]) changes in pike perch Sander lucioperca stored in ice were investigated. The same soaking time was used for both gillnet and longline fishing. The catching method had considerable influence on the freshness quality of pike perch. The acceptable shelf life was 15 days for pike perch caught by gillnet, and 22 days for longline and harpoon. The initial concentrations of inosine monophosphate (2.4 μmol/g) in pike perch caught by gillnet were significantly lower ( P  < 0.05) than longline (4.1 μmol/g), and especially by harpoon (16.7 μmol/g). However, the initial K -values for fish caught by harpoon were significantly ( P  < 0.05) lower (24.36%) than fish caught by longline and gillnet (57.69%, 64.41%, respectively). The average K , Ki, G and H -values at rejection day in terms of sensory assessment were approximately 90, 98, 156 and 40%, respectively, for all catching methods during ice storage. However, TVC reached 7.0 log cfu/g after approximately 11 days of storage for fish caught by gillnet, 19 days for fish caught by longline and 8 days for fish caught by harpoon. The result of this study suggests that the best catching method for preserving the freshness of pike perch is longline, based on the data obtained from the sensory and microbiological analysis.     

Organization and sequence of four flagellin-encoding genes of Edwardsiella ictaluri

Edwardsiella ictaluri , the cause of enteric septicaemia in channel catfish ( Ictalurus punctatus ), is motile by means of peritrichous flagella. We determined the complete flagellin gene sequences and their organization in E. ictaluri by sequencing genomic segments from a λ-ZAP phage genomic library of E. ictaluri . Four flagellin genes ( fliC1, fliC2, fliC3 and fliC4 ) are arranged in tandem within 6 kb in the E. ictaluri genome. Each flagellin-coding sequence is preceded by a σ²⁸ recognition site consensus sequence. The predicted amino acid sequences of all four flagellin proteins (between 36 and 37.5 kDa) are similar in the N-terminal (1–160 aa) and C-terminal (last 74 aa) portions and are divergent in the central portion of the proteins. Proteins encoded by flC1, fliC2 and fliC3 are more similar to each other (88–90% aa identity) than to the protein encoded by fliC4 (76–78% aa identity). basic local alignment search tool analysis of GenBank sequences showed that all flagellin aa sequences are more similar to those of Serratia marcescens (72–74% identity) than to those of Edwardsiella tarda (≤64% identity). Primary determination of E. ictaluri flagellin gene sequences facilitate advanced studies on the role of flagella in host–pathogen interaction.     

Purification and characterization of lipovitellin from Pacific saury Cololabis saira

ABSTRACT:   Lipovitellin (Lv), the major yolk protein derived from vitellogenin (Vg), was purified from vitellogenic ovaries of Pacific saury Cololabis saira using hydroxylapatite column chromatography followed by gel filtration. The apparent native mass of purified Lv was approximately 420 kDa, while the tertiary structure of Lv revealed by sodium dodecylsulfate–polyacrylamide gel electrophoresis was typical of teleost Lvs, consisting of a heavy chain (∼99 kDa) and a light chain (∼34 kDa). Western blot analysis using rabbit antiserum raised against Pacific saury Lv revealed a specific reaction with a polypeptide (∼194 kDa) that is present in serum from female Pacific saury but not in male serum, suggesting the approximately 194-kDa polypeptide to be the Vg monomer. This study describes the first step toward the development of specific immunoassays for Pacific saury Vg, which will be an effective tool for monitoring the reproductive development of this species.