Ontogenetic dietary shifts of largemouth bass do not increase trophic position in a shallow eutrophic lake in Japan

The trophic positions of top predators can provide useful information for estimating the length of food chains and for assessing the impacts of invasive species or the bioaccumulation of harmful compounds. In aquatic ecosystems, large carnivorous fishes may change their trophic positions ontogenetically. We used stable carbon and nitrogen isotope ratios to test the hypothesis that the trophic positions of largemouth bass, top predators in Lake Izunuma, Japan, would increase with total length (TL) as a result of ontogenetic shifts in diet. Results from a stable isotope analysis in R mixing model indicated that largemouth bass <100 mm TL fed mostly on zooplankton and small omnivorous fishes, while individuals from 100 to 199 mm TL size class relied more heavily on small omnivorous fishes. Red swamp crayfish Procambarus clarkii were a major food source for largemouth bass ≥200 mm TL. However, the trophic positions of largemouth bass did not increase with the dietary shift from zooplanktivory to piscivory, and actually decreased when larger fish shifted towards feeding on red swamp crayfish. In Lake Izunuma, the trophic positions of small omnivorous fishes and red swamp crayfish were not higher than those of zooplankton. This explains why the largest largemouth bass occupied lower trophic positions than smaller individuals. Our results suggest that the body size of carnivorous fishes should be taken into consideration when using their trophic positions as top predators to evaluate aquatic systems.Trophic positions of largemouth bass Micropterus salmoides in Lake Izunuma, Japan, did not increase with the dietary shift from zooplanktivory to piscivory, and actually decreased when larger fish shifted towards feeding on red swamp crayfish. Consequently, largemouth bass ≥300 mm TL occupied lower trohic positions than smaller individuals

Visualization and motility of primordial germ cells using green fluorescent protein fused to 3'UTR of common carp nanos-related gene

Primordial germ cells (PGCs) are the only cells in developing embryos with the potential to transmit genetic information to the next generation. We previously visualized the PGCs of several teleostean embryos by injecting RNA synthesized from constructs encoding green fluorescent protein (GFP) fused to the 3'UTR of the zebrafish (Danio rerio) nanos1 gene (nos1). However, this technique was not always suitable for visualizing PGCs in embryos from all teleost species. In this study, we compared the visualization of PGCs in common carp (Cyprinus carpio) embryos using two artificial constructs containing GFP fused to the 3'UTR of nanos from either common carp or zebrafish. Visualization was better using GFP fused to the 3'UTR of the nanos gene from common carp, compared with that from zebrafish. The visualized PGCs successfully migrated toward the gonadal ridge after transplantation into goldfish host embryos, suggesting that they maintained normal migratory motility. These techniques could be useful for the production of inter-specific germline chimeras using common carp donor PGCs

Developmental potential of somatic and germ cells of hybrids between Carassius auratus females and Hemigrammocypris rasborella males

The cause of hybrid sterility and inviability has not been analyzed in the fin-fish hybrid, although large numbers of hybridizations have been carried out. In this study, we produced allo-diploid hybrids by cross-fertilization between female goldfish (Carassius auratus) and male golden venus chub (Hemigrammocypris rasborella). Inviability of these hybrids was due to breakage of the enveloping layer during epiboly or due to malformation with serious cardiac oedema around the hatching stage. Spontaneous allo-triploid hybrids with two sets of the goldfish genome and one set of the golden venus chub genome developed normally and survived beyond the feeding stage. This improved survival was confirmed by generating heat-shock-induced allo-triploid hybrids that possessed an extra goldfish genome. When inviable allo-diploid hybrid cells were transplanted into goldfish host embryos at the blastula stage, these embryos hatched normally, incorporating the allo-diploid cells. These allo-diploid hybrid cells persisted, and were genetically detected in a 6-month-old fish. In contrast, primordial germ cells taken from allo-diploid hybrids and transplanted into goldfish hosts at the blastula stage had disappeared by 10 days post-fertilization, even under chimeric conditions. In allo-triploid hybrid embryos, germ cells proliferated in the gonad, but had disappeared by 10 weeks post-fertilization. These results showed that while hybrid germ cells are inviable even in chimeric conditions, hybrid somatic cells remain viable

Skewed genetic sex ratio in reciprocal hybrids between pink salmon and masu salmon

サケ科魚類の人為雑種において，性比が一方に偏る例が報告されてきたが，これらは生殖腺の表現型に基づく。本研究では，カラフトマスとサクラマス間の正逆雑種について，雄特異的な性決定遺伝子sdYの有無による遺伝的性を検討した。その結果，カラフトマス雌×サクラマス雄，サクラマス雌×カラフトマス雄の8か月齢魚の遺伝的性は雌に，サクラマス雌×カラフトマス雄の12か月齢魚は雄に偏った。初期胚と孵化仔魚の遺伝的性比は1:1であったことから雑種の性比の偏りは成長過程における生残率の雌雄差により生じたと考えられた。Skewed sex ratio has often been observed in hybrids, but the sex was always determined by gonadal phenotypes. Here, we artificially induced reciprocal hybrids between pink salmon and masu salmon and then examined the genetic sex ratio in the hybrids based on the presence or absence of the sex-determining gene sdY. As a result, the sex of 8-month-old hybrids between pink salmon female x masu salmon male and masu salmon female x pink salmon male skewed to female, while 12-month-old hybrids between masu salmon female x pink salmon male were exclusively male. Since the sex ratio between the early embryos and hatching alevin was 1:1, it was considered that the skewed sex ratio was due to the difference of survival rate between genetic males and females

Prescription Surveillance and Polymerase Chain Reaction Testing to Identify Pathogens during Outbreaks of Infection

Syndromic surveillance, including prescription surveillance, offers a rapid method for the early detection of agents of bioterrorism and emerging infectious diseases. However, it has the disadvantage of not considering definitive diagnoses. Here, we attempted to definitively diagnose pathogens using polymerase chain reaction (PCR) immediately after the prescription surveillance system detected an outbreak. Specimens were collected from 50 patients with respiratory infections. PCR was used to identify the pathogens, which included 14 types of common respiratory viruses and Mycoplasma pneumoniae. Infectious agents including M. pneumoniae, respiratory syncytial virus (RSV), rhinovirus, enterovirus, and parainfluenza virus were detected in 54% of patients. For the rapid RSV diagnosis kit, sensitivity was 80% and specificity was 85%. For the rapid adenovirus diagnosis kit, no positive results were obtained; therefore, sensitivity could not be calculated and specificity was 100%. Many patients were found to be treated for upper respiratory tract infections without the diagnosis of a specific pathogen. In Japan, an outbreak of M. pneumoniae infection began in 2011, and our results suggested that this outbreak may have included false-positive cases. By combining syndromic surveillance and PCR, we were able to rapidly and accurately identify causative pathogens during a recent respiratory infection outbreak