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Settlement success and post-settlement survival of Acropora sp. aff. tenuis spat within a small bay in Japan
Get PDFThe early life history of scleractinian corals is largely unknown. In this study, we compared the settler numbers and post-settlement survival of Acropora aff. tenuis larvae on a square hollow section (SHS) substrate at 10 stations and 2 depths (20 sites in total) from the mouth to the back of a small bay. The number of settlers tended to be lower at the back of the bay. Survival rates at 15 mo after settlement were 2.5 times higher in the shallower waters at the back of the bay, while they were 2.5 times higher in the deeper waters at the middle and mouth of the bay. Water depth and temperature, photon flux, current velocity, sedimentation, water column and interstitial water nutrients, and algal cover were measured at each site, and a significant correlation was found between settler numbers and sedimentation. The best models of physical environmental factors affecting post-settlement survival in each monitoring period showed that daylight intensity on sunny days and algal cover had a negative effect on survival 3 and 15 mo after settlement. It is unlikely that light intensity would have a negative effect on corals, for which symbiosis with zooxanthellae is essential, but it is partly expected that the effects of algal cover and water depth on the light environment in the microhabitats within the SHS would vary with the environmental gradient in the bay. This study suggests that the relationship between environmental factors and juvenile coral survivorship is complex even within a small bay.journal articl
Hierarchical diversity partitioning of microscopic epibiont community on intertidal molluscan shells and inert surfaces over three geographic regions in Japan
Get PDFMicroscopic epibionts on molluscan shells are a component of the biodiversity of intertidal coastal areas. Because molluscan shells are discrete habitats for the epibiont community, and the molluscan basibionts belong to the local community, epibiont diversity can be evaluated hierarchically by basibiont categories including species. To evaluate the structure of epibiont diversity and effects of taxonomic resolution on the evaluation, epibionts on molluscan shells and inert surfaces were investigated at three geographically distant sites in Japan. In total, 94 species-level taxonomic units of epibionts were obtained from 31 basibiont molluscan species and inert surfaces (plastics and rock chips). The density and the species richness at the site of the lowest latitude were significantly lower than those at the other sites. The epibiont community differed between the three sites, although the major portion of the epibionts were diatoms. Between-site diversity contributed most of the total diversity of the species richness and Simpson diversity in the five levels of the hierarchical partitioning: sample (individual basibiont), basibiont species (molluscan species), surface group (bivalves, chitons + limpets, and globose gastropods), site, and the total. The taxonomic resolution did not markedly affect the variability of communities between the three sites, although the taxon richness was reduced to 51 in the genus-level analysis. The lower taxonomic resolution (genus level); however, increased the contribution of the within-sample and decreased the contribution of β diversities at the higher hierarchies, leading to a possible overestimation of biotic homogenization between the communities.journal articl
Year-Round Long Photoperiod (Ld 16:8) Suppresses Sexual Maturation in Masu Salmon (Oncorhynchus Masou)
Get PDFMariculture industries for several salmonid species have been expanded in many areas in Japan. Endemic masu salmon (Oncorhynchus masou) is among them and is promising due to its scarcity value and good taste. However, early sexual maturation before harvest size is a major issue because it results in substantial economic loss due to the retardation of somatic growth. Therefore, methods for delaying or inhibiting early maturation need to be established. To accomplish this, countermeasures for sexual maturation using photoperiod manipulation were studied. Under-yearling (10-month-old) smolts were reared under three experimental regimes in fresh water from summer (August 2019) to autumn in the next year (September 2020) as follows: simulated natural photoperiod (SNP group), constant long photoperiod at LD 16:8 (LP group), and alternating photoperiod between long (LD 16:8, from August to October 2019 and from April to July 2020) and short (LD 8:16, from October 2019 to April 2020) ones (LSP group). Ten to 40 fish from each group were sampled at a 12-week interval and the gonadosomatic index, gonadal histology, serum sex steroids, and gene expressions of two gonadotropins, namely the follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), beta subunits (fshb and lhb) in the pituitaries were examined to assess sexual maturation. Rearing under constant long photoperiod (LP group) strongly inhibited the gonadal maturation of salmon. Meanwhile, most fish in the SNP and LSP groups started vitellogenesis or spermatogenesis in July 2020. The continuous long photoperiod also suppressed the increase of the fshb and lhb expression levels and serum levels of 17β-estradiol in females and 11-ketotestosterone in males. This inhibition of sexual maturation through a long-term long photoperiod is applicable for masu salmon aquaculture.journal articl
オチバガイの各体部位と殻長との相対成長 ─殻長サイズ復元のためのアロメトリー式
Get PDFGari virescens (Psammobiidae) is a near-threatened bivalve species that inhabits tidal flats in Japan. Recently, it has been frequently detected in the gut contents of tidal flat fishes. The purpose of this study is to establish regression formulas for reconstructing the shell length (SL) of predated specimens. Therefore, we clarified the relative growth relationship between body parts of the bivalve and its SL using specimens from the western Seto Inland Sea of Japan. The allometric regression formula for estimating SL (mm) from shell height (SH, mm) was SL = 1.53 × SH1.0657 (r = 0.998, n = 66, P < 0.01), and the formula for estimating SL (mm) from foot length (FL, mm) was SL = 1.82 × FL1.0478 (r = 0.969, n = 39, P < 0.01). In addition, we established several other regression formulas for estimating SL. As a case study of applying these formulas, we reconstructed the SL of specimens predated by the fish Acanthopagrus schlegelii. These allometric formulas enable the reconstruction of SL from body parts and shells broken during predation.journal articl
A novel birnavirus identified as the causative agent of summer atrophy of pearl oyster (Pinctada fucata (Gould))
Get PDFThe Akoya pearl oyster (Pinctada fucata (Gould)) is the most important species for pearl cultivation in Japan. Mass mortality of 0-year-old juvenile oysters and anomalies in adults, known as summer atrophy, have been observed in major pearl farming areas during the season when seawater temperatures exceed about 20 °C since 2019. In this study, we identified a novel birnavirus as the pathogen of summer atrophy and named it Pinctada birnavirus (PiBV). PiBV was first presumed to be the causative agent when it was detected specifically and frequently in the infected oysters in a comparative metatranscriptomics of experimentally infected and healthy pearl oysters. Subsequently, the symptoms of summer atrophy were reproduced by infection tests using purified PiBV. Infection of juvenile oysters with PiBV resulted in an increase in the PiBV genome followed by the atrophy of soft body and subsequent mortality. Immunostaining with a mouse antiserum against a recombinant PiBV protein showed that the virus antigen was localized mainly in the epithelial cells on the outer surface of the mantle. Although the phylogenetic analysis using maximum likelihood method placed PiBV at the root of the genus Entomobirnavirus, the identity of the bi-segmented, genomic RNA to that of known birnaviruses at the full-length amino acid level was low, suggesting that PiBV forms a new genus. The discovery of PiBV will be the basis for research to control this emerging disease.journal articl
Mass mortality events associated with cyprinid herpesvirus 2 (CyHV-2) infection in wild Prussian carp Carassius gibelio in the Netherlands, and molecular biology of virus strains
Get PDFIn 2011 and 2015, four mass mortalities of Prussian carp (Carassius gibelio) were observed in a recreational freshwater lake and open freshwater in the western part of the Netherlands. Cyprinid herpesvirus 2 (CyHV-2) infection was suspected in these cases, based on presumptive gross diagnosis. To elucidate the cause of the mass mortalities diagnostic PCR assays were performed for CyHV-2, based on the helicase gene. Furthermore, the viral isolates were genotyped by sequencing the enlarged marker A and marker B sequences. Diagnostic PCR revealed that three of four samples were positive for CyHV-2, indicating these three mass mortalities were associated with CyHV-2 infection. The marker A sequence from one of the isolates found in this study was identical to those from different locations such as Asia and Middle East, suggesting a link among the isolates. This is the first detailed report on mass mortalities of Prussian carp associated with CyHV-2 infection in natural aquatic environments in the Netherlands. Since 2015, additionally, in total three CyHV-2 associated outbreaks of Dutch Prussian carp were seen in 2016 and 2020. These outbreaks in Prussian carp from lakes and open water suggest that the virus has been spreading in natural freshwaters in the Netherlands.journal articl
Investigation of the preference of marlin Kajikia audax sashimi with different lipid contents through sensory evaluation
Get PDFIdentifying the sensory properties of fish consumers is important for providing their preferred seafood. Odor, flavor, texture, and appearance affected the sensory preference for fish. Moreover, several compounds are involved in sensory preference. This study focused on lipids that affect preference for seafood and examined the lipid content preference in marlin Kajikia audax sashimi. First, lipid contents and fatty acid compositions of different individual sizes and body parts of marlin were compared. Next, the preference for overall, taste, texture, odor, aftertaste, and lipid content in marlin sashimi taken from different parts of the body with different amounts of lipids was investigated using the paired preference method. Then the relationship of lipid content preference with other preferences were also evaluated using the Chi-square test. The crude lipid of big-sized marlin (51.1–55.1 kg) was 9.5%−13.2%, and the crude lipid of small-sized marlin (23.5–30.0 kg) was 0.8%−1.2%. The dorsal parts of big-sized marlin had lipid contents in the anterior parts higher than those in the posterior parts (p < 0.05). Whereas no differences were observed in the fatty acid composition of different body parts. The lipid content preference for the anterior dorsal part (high lipid part) was higher than that for the posterior dorsal part (lower lipid part) (p < 0.05). However, no difference in overall preference was observed. Additionally, the relationship between lipid content preference and other preference were indicated that the high lipid content parts preferred group significantly preferred the high lipid content parts at overall and taste evaluation (p < 0.01). On the other hand, the low lipid content parts preferred groups showed opposite evaluation. Therefore, the lipid content was associated with the preference for marlin sashimi and be classified into two groups: one prefers high lipid sashimi and the other prefers low lipid sashimi.journal articl