Plecoglossus Research Articles

Ichthyofaunal Assemblage of the Dianshan Lake, Shanghai, China: Implications for Management

Ichthyofaunal diversity of the Dianshan lake in Shanghai, China was assessed during the year 2013 from samples of finfish harvested using fleets of gillnets and trawls of different mesh sizes with the aim of generating necessary data that could support sustainable use of finfish in this lake. Morphometric parameters of specimens caught were taken following standard procedures. Totally 21,308 specimens belonging to 40 species, 15 families and 7 orders were encountered throughout the study period. Seasonal abundance was lowest (395 individuals) during March (spring) and highest (4428 individuals) during August (summer). Cyprinidae was the dominant family (22 species) and Coilia ecetenes taihuensis was the most abundant species (30.69%), followed by Acheilognathus taenianalis (17.8618%), Plagiognathops microlepis (16.567%), Carassius auratus (14.492%). The evenness, richness and biodiversity of the faunal assemblage were also evaluated by Shannon–Wiener index (H′), Margalef’s diversity Index (d) and evenness index (J) respectively. Hypophthalmichthys nobilis was the largest and heaviest fish (34.909 cm, FL; 889.355 g, W), the smallest fish in length recorded was Odontamblyopus rubicundus (4.19 cm) while Plecoglossus altivelis altivelis (1.1 g) was the lowest in terms of mean weight. The mean condition factor for all fish species was (K = 1.72), showing fish species were generally in ‘good’ condition. Fluctuations in species occurrence and abundance noted in our study may be accounted from the variation in the physico-chemical parameters of the Lake in respect to time. But, under such a situation it is evident that the small fish species increased to a great extent and a few like Coilia ecetenes taihuensis became the dominant.

CXCR3.1 and CXCR3.2 Differentially Contribute to Macrophage Polarization in Teleost Fish.

The study of multiple copies of chemokine receptor genes in various teleosts has long appealed to investigators seeking to understand the evolution of the immune system. The CXCR CXCR3 gene has two isoforms, CXCR3.1 and CXCR3.2, which are both expressed in macrophages. The distinct roles of teleost CXCR3s have not been identified previously. In this article, we found that CXCR3.1 and CXCR3.2 differentially contributed to macrophage polarization in the teleosts: ayu (Plecoglossus altivelis), grass carp (Ctenopharyngodon idella), and spotted green pufferfish (Tetraodon nigroviridis). In ayu macrophages, the P. altivelis CXCR3.1 (PaCXCR3.1) gene was constitutively expressed, whereas the P. altivelis CXCR3.2 (PaCXCR3.2) gene was induced postinfection with Escherichia coli Upon E. coli infection, PaCXCR3.1+ and PaCXCR3.2+ macrophages showed an M1 and an M2 phenotype, respectively. CXCL9-11-like proteins mediated M1 and M2 polarization by interacting with the PaCXCR3.1 and PaCXCR3.2 proteins on macrophages, respectively. The transcription factors P. altivelis STAT1 and P. altivelis STAT3 were activated in PaCXCR3.1+ and PaCXCR3.2+ macrophages, respectively. Furthermore, the prognosis of septic ayu adoptively transferred with PaCXCR3.2+ macrophages was improved. Our data reveal a previously unknown mechanism for macrophage polarization, suggesting that redundant genes may regulate crucial functions in the teleost immune system.

Stochastic optimization model of aquacultured fish for sale and ecological education

A stochastic optimization model for management of aquacultured fish for sale and ecological education is established. Population dynamics of the fish is described with a system of stochastic differential equations assuming that they are stochastically harvested after an opening time: the variable to be optimized. A remarkable difference between the present and conventional models for the aquaculture is that the former considers the harvesting for ecological education, which is a key for current inland fishery especially in Japan. Finding the cost-effective optimal opening time effectively reduces to solving an algebraic equation. Mathematical analysis on the optimal opening time clearly reveals its unique existence and qualitative behavior, such as its dependence on the model parameters, which have practical implications. A demonstrative application example of the model is also presented focusing on an aquaculture of Plecoglossus altivelis in Japan.

Occurrence and distribution of yellow grub trematodes (Clinostomum complanatum) infection in Taiwan.

Digenetic trematodes of the genus Clinostomum are widely distributed in many species of freshwater fish and are known to cause the zoonotic disease Halzoun. Humans may become accidental hosts if they ingest raw freshwater fish containing metacercaria of Clinostomum complanatum, which causes pharyngitis or laryngitis. The yellow grub parasitizing cultivated ayu (Plecoglossus altivelis) and loach (Misgurnus anguillicaudatus) was one of the most serious problems in fish farms from 1977 to 1979 in Taiwan. The present study revealed, for the first time, frequent occurrence of C. complanatum metacercaria in various fish species in a natural environment, the Dahan River, in Taiwan. We examined 1503 fish specimens belonging to four families and 162 snails representing six species. C. complanatum metacercaria was mainly from the fish family Cyprinidae, and only cercaria from the snail Radix swinhoei was recovered. The prevalence and mean intensity of metacercaria were 9.8% and 9.35 parasites/infected fish, respectively. The prevalence of cercaria was low, 0.62%, in snails. Acrossocheilus paradoxus, Zacco barbata, Zacco pachycephalus, Zacco platypus, Onychostoma barbatula, and Hemibarbus labeo are new host records. Metacercariae were primarily found in the operculum, mandible, muscle, and oral cavity of fish. Morphological description and molecular analysis with 18S rDNA sequencing allowed for rapidly identifying C. complanatum. Encysted and excysted metacercariae cultivated at 22°C in physiological saline died within 60h. The mean intensity of infection increased with an increasing length of Z. pachycephalus. We found no association between monthly parasite prevalence and mean intensity at each sampling location. No C. complanatum metacercaria survived after 8h of salting. The Dahan River has suitable conditions and hosts (snails, fish, and fish-eating birds) for maintaining the life cycle of C. complanatum.

Water temperature-dependent degradation of environmental DNA and its relation to bacterial abundance.

Environmental DNA (eDNA) is DNA shed by organisms into surrounding environments such as soil and water. The new methods using eDNA as a marker for species detection are being rapidly developed. Here we explore basic knowledge regarding the dependence of the eDNA degradation rate on time and water temperature, and the relationship between eDNA degradation and bacterial abundance. This subject has not been well clarified, even though it is essential for improving the reliability of eDNA analysis. To determine the time- and water temperature-dependent degradation of eDNA, river water was sampled and eDNA concentrations were determined for ayu sweetfish (Plecoglossus altivelis altivelis) and common carp (Cyprinus carpio) at seven time points, over a 48-h period, and at three different water temperatures. The degradation of eDNA was modeled for each species using an existing exponential decay model with an extension to include water temperature effects. The degradation models were constructed for ayu sweetfish as Nt = 229,901.2 × exp [− (0.01062 × k − 0.07081) × t] and for common carp as Nt = 2,558.0 × exp [− (0.01075 × k − 0.07372) × t]. Nt is the DNA concentration at time t (elapsed time in hours) and k is the water temperature (°C). We also measured the concentration of eDNA derived from purified genomic DNA of the common carp, which was spiked into aquarium water without the target species, and we measured the bacterial abundance in the sample water after 12 and 24 h of incubation. Environmental DNA degradation was accelerated at higher water temperatures (generalized linear model, GLM; p < 0.001), but bacterial abundance did not have a significant effect on eDNA degradation (GLM, p = 0.097). These results suggest that the proper treatment of this temperature effect in data interpretations and adjustments would increase the reliability of eDNA analysis in future studies.

Studies on the specific growth of fresh-water fishes referring to the weight increase of individual and population. III. : Growth of the pond-reared Ayu-fish, Plecoglossus altivelis T. and S., with special reference to the significance of their social behaviour in eliminating the possible growth-improving effect of feeding by many food-balls.

Studies on the specific growth of fresh-water fishes referring to the weight increase of individual and population. III. : Growth of the pond-reared Ayu-fish, Plecoglossus altivelis T. and S., with special reference to the significance of their social behaviour in eliminating the possible growth-improving effect of feeding by many food-balls.

Studies on the specific growth of freshwater fishes referring to the weight increase of individual and population. II. : Growth of the pond-reared Ayu-fish, Plecoglossus altivelis T. and S., with special reference to the population density and the dispersion of growth among members.

Studies on the specific growth of freshwater fishes referring to the weight increase of individual and population. II. : Growth of the pond-reared Ayu-fish, Plecoglossus altivelis T. and S., with special reference to the population density and the dispersion of growth among members.

Optimization model to start harvesting in stochastic aquaculture system

Establishment of cost‐effective management strategy of aquaculture is one of the most important issues in fishery science, which can be addressed with bio‐economic mathematical modeling. This paper deals with the aforementioned issue using a stochastic process model for aquacultured non‐renewable fishery resources from the viewpoint of an optimal stopping (timing) problem. The goal of operating the model is to find the optimal criteria to start harvesting the resources under stochastic environment, which turns out to be determined from the Bellman equation (BE). The BE has a separation of variables type structure and can be simplified to a reduced BE with a fewer degrees of freedom. Dependence of solutions to the original and reduced BEs on parameters and independent variables is analyzed from both analytical and numerical standpoints. Implications of the analysis results to management of aquaculture systems are presented as well. Numerical simulation focusing on aquacultured Plecoglossus altivelis in Japan validates the mathematical analysis results. Copyright © 2017 John Wiley &amp; Sons, Ltd.

An optimal management strategy for stochastic population dynamics of released Plecoglossus altivelis in rivers

Excessive predation pressure from the waterfowl Phalacrocorax carbo (Great Cormorant) on Plecoglossus altivelis (Ayu) has recently been a severe problem of river environment in Japan. Local fishery cooperatives are currently suffering from economic difficulties due to decrease of the fish catch of P. altivelis. Local fishery cooperatives and municipalities have been enthusiastically trying to develop countermeasures that can effectively reduce the predation pressure; however, their effectiveness and efficiency have not been systematically quantified well. This aim can be achieved with the help of an appropriate mathematical model. In this paper, based on a pure death process, a practical stochastic control model for population dynamics of released P. altivelis in river environment under predation pressure from P. carbo, harvesting by human, and environmental fluctuations is proposed. Finding an optimal management strategy ultimately reduces to solving a 2D Hamilton–Jacobi–Bellman equation, which is performed with a finite element scheme. Its application to a Japanese river environment successfully computes the optimal management strategy that is consistent with the reality. Numerical sensitivity analysis of the presented mathematical model is also performed for comprehension of dependence of the optimal strategy on the model parameters.

Development of immersion vaccine for bacterial cold-water disease in ayu Plecoglossus altivelis.

Flavobacterium psychrophilum (F. psychrophilum) is the causative agent of bacterial cold-water disease (BCWD) that occurs in ayu Plecoglossus altivelis. Formalin-killed cell of F. psychrophilum has long been studied as an immersion vaccine for BCWD. In this study, we explored the possibility of F. psychrophilum collagenase (fpcol) for use as the immersion vaccine. BCWD convalescent ayu sera contained specific IgM antibodies against somatic F. psychrophilum and fpcol, meaning that fpcol is a promising antigen for the vaccine development. The recombinant fpcol was successfully expressed in Escherichia coli and Brevibacillus chosinensis (B. chosinensis). The culture supernatant of the B. chosinensis was used as an immersion vaccine solution. The vaccinated ayu were then challenged by soaking into F. psychrophilum culture. In two experimental groups, the relative percentages of survivals were 63 and 38%, respectively, suggesting that fpcol is promising as the immersion vaccine for ayu-BCWD.

Rapid and effective isolation of candidate sequences for development of microsatellite markers in 30 fish species by using kit-based target capture and multiplexed parallel sequencing

Recent advances in next-generation sequencing (NGS) technology have accelerated the development of microsatellite markers for wildlife conservation genetics. Although the discovery of microsatellite-containing sequences based on NGS is more efficient with sequencing of a microsatellite-enriched library than with whole-genome shotgun sequencing, the process of constructing a microsatellite-enriched library is somewhat complicated. Therefore, many researchers prefer to use external services for the microsatellite-enrichment, which requires more time. To facilitate the rapid and effective development of novel microsatellite markers, we attempted to simplify the process of constructing a microsatellite-enriched library for multiplexed parallel sequencing. To capture microsatellite-containing sequences, we applied an easy-to-use commercially available kit for the hybridization and wash steps. After preparing shotgun libraries of 30 fish species for NGS, we captured microsatellite-containing DNA fragments directly from the shotgun libraries by using the commercially available kit. Next, three runs of multiplexed parallel sequencing were conducted on the 454 GS Junior platform. The resulting sequences for each species included high proportions of microsatellite-containing sequences (from 46 to 79%). Thus, sufficient numbers of primer sets, ranging from 1029 to 6606, were effectively designed for each species. Microsatellite capture and sequencing were completed in about a week, so the time required was substantially reduced. To validate the effectiveness of our strategy, we screened 44 potential primer sets designed for ayu (Plecoglossus altivelis). The results of polymorphisms revealed that allelic variability at 23 markers will be useful for studying population structure. These results prove the effectiveness of our improved approach for microsatellite marker development.

Molecular identification and functional analysis of KLF2 in Plecoglossus altivelis (ayu): It's regulatory role in monocyte/macrophage activation

Monocytes/macrophages (MO/MФ) play an important role in the response to infection in Plecoglossus altivelis (ayu). However, the role of transcription factors in the function of ayu MO/MФ is poorly understood. Here, we cloned the cDNA sequence of the Kruppel-like factor 2 (PaKLF2) gene from ayu. Phylogenetic analysis indicated that PaKLF2 was closest to that of Atlantic salmon (Salmo salar). Real time quantitative PCR (RT-qPCR) revealed that the PaKLF2 mRNA level was highest in the peripheral blood mononuclear cells among all tested tissues. The mRNA expression of PaKLF2 was upregulated in the head kidney, liver, spleen, and brain after Listonella anguillarum infection. Subsequently, PaKLF2 was expressed and purified to prepare anti-PaKLF2 antibodies. After L. anguillarum challenge, the PaKLF2 mRNA and protein levels were significantly upregulated in ayu MO/MФ. Moreover, PaKLF2 knockdown in MO/MФ resulted in the enhancement of cytokine production as well as phagocytotic and bactericidal capability. Therefore, PaKLF2 may modulate the immune response in ayu by suppressing the function of MO/MФ.

Optimal Installation of Overhead Lines (Tegusu) to Reduce Predation from Piscivorous Birds to &lt;i&gt;Plecoglossus altivelis&lt;/i&gt; (Ayu) Taking into Account of Its Decaying Protection Effect

Optimal Installation of Overhead Lines (Tegusu) to Reduce Predation from Piscivorous Birds to &lt;i&gt;Plecoglossus altivelis&lt;/i&gt; (Ayu) Taking into Account of Its Decaying Protection Effect

LC-MS/MSによるアユ（&lt;i&gt;Plecoglossus altivelis&lt;/i&gt;）中のフェニコール系薬剤の分析

An analytical method for the determination of residues of 3 phenicol drugs (chloramphenicol, thiamphenicol and florfenicol) in Ayu (Plecoglossus altivelis) by LC-MS/MS was developed. We used the whole body of Ayu, including the bones and internal organs, in addition to muscle. Phenicols were extracted with 90% acetonitrile and an aliquot of the crude extract was cleaned up on a Florisil column (2 g), followed by defatting with n-hexane. The acetonitrile extract was evaporated and the solvent was replaced with phosphate buffer, then the extract was purified on a hydroxylated styrene-divinylbenzene copolymer column (200 mg). Finally, sample solution was passed through a deproteination cartridge filter with a lipid removal function. Chloramphenicol was quantitated by means of a calibration curve corrected with salogate standard (chloramphenicol-d5) and thiamphenicol and florfenicol were quantitated based on absolute calibration curves. This method was validated in accordance with the notification of the Ministry of Health, Labour and Welfare of Japan. As a result of the validation study, the trueness, repeatability and within-laboratory reproducibility were 85-103, 5-13 and 8-13%, respectively. This method is useful for inspecting residues of 3 phenicol drugs in whole body of Ayu efficiently. Moreover, when chloramphenicol and thiamphenicol are detected by this method, the quantitated value is applicable to decide the compliance of the sample with the specifications and standards of the Food Sanitation Law.

Expression of ayu antimicrobial peptide genes after LPS stimulation.

Plecoglossus altivelis (ayu) is one of the most important fish species in the Japanese islands and in internal fish hatcheries. Living in open aquatic environments exposes fish to many pathogens. Therefore, they require rapid and strong immune defenses. We investigated in vivo the direct association between the ayu innate immune response, represented by the relative transcription of genes encoding the cathelicidin and hepcidin antimicrobial peptides, and lipopolysaccharide (LPS), a conventional pathogen-associated molecular patterns (PAMPs) of Gram-negative bacteria. Different concentrations of LPS (1, 10 and 100 µg/fish) were injected intraperitoneally into young (sexually immature) and adult (fully sexually mature) ayu. The relative expression of the antimicrobial peptide genes was measured 6 hr, 24 hr and 1 week after stimulation with LPS. We found a direct association between the expression of the antimicrobial peptide genes investigated and LPS stimulation. This relationship was time-, dose- and age-dependent. Further research is required to determine the cell-specific transcriptional regulation and posttranscriptional regulation of these antimicrobial peptides.

奈半利川におけるアユの生息数と減耗率の潜水目視法による推定

奈半利川におけるアユの生息数と減耗率の潜水目視法による推定

Measurement of otolith Sr/Ca ratios in heat-cooked ayu Plecoglossus altivelis altivelis for stock identification

Measurement of otolith Sr/Ca ratios in heat-cooked ayu Plecoglossus altivelis altivelis for stock identification

Modeling Rheotaxis based on Preference to Predict Fish Migration Behavior in A River

In this research, we attempt to determine preference of rheotaxis and estimated weight values in laboratory experiments using adult and juvenile ayu (Plecoglossus altivelis altivelis). We conducted paired comparisons of ayu distribution between the upper and lower sections of a test watercourse using several velocity conditions (10, 30, and 40 cm/s for juveniles; 20, 30, 50, 70, and 90 cm/s for adults). In upper watercourse sections, juvenile ayu preferred velocities of 30 cm/s and 40 cm/s, and adults preferred a velocity of 50 cm/s. Even when a highly preferred illumination condition of 4000 lux was present in the lower section, fish maintained a higher distribution in the upper section. We design a procedure to calculate rheotaxis preference and built it into our fish behavior simulation model on geographic information system (GIS) software. The model successfully predicted natural migration behavior of fish.

Environmental DNA analysis for estimating the abundance and biomass of stream fish

Summary Environmental DNA (eDNA) analysis for detecting the presence of aquatic and terrestrial organisms is an established method, and the eDNA concentration of a species can reflect its abundance/biomass at a site. However, attempts to estimate the abundance/biomass of aquatic species using eDNA concentrations in large stream and river ecosystems have received little attention. We determined the eDNA concentration and abundance/biomass of a stream fish, Plecoglossus altivelis, by conducting a snorkelling survey in the Saba River, Japan. Furthermore, we evaluated the relationship between eDNA concentrations and the estimated abundance/biomass of P. altivelis, and determined its spatial distribution within the river. Across the three seasons from spring to autumn, we found significant correlations between the eDNA concentration of P. altivelis and its abundance/biomass at study sites within the river. We detected the eDNA at the sites where we found only feeding traces on stones (where P. altivelis was not directly observed), but not at sites without feeding traces. Additionally, we tested the optimal number of qPCR replicates needed for the eDNA evaluation of P. altivelis abundance and biomass; only a small number of replicates was required when the eDNA concentration was high. Our findings suggest that eDNA analysis is a useful tool to estimate fish abundance/biomass as well as their spatial distribution in rivers.

Mathematical analysis and validation of an exactly solvable model for upstream migration of fish schools in one-dimensional rivers

Upstream migration of fish schools in 1-D rivers as an optimal control problem is formulated where their swimming velocity and the horizontal oblateness are taken as control variables. The objective function to be maximized through a migration process consists of the biological and ecological profit to be gained at the upstream-end of a river, energetic cost of swimming against the flow, and conceptual cost of forming a school. Under simplified conditions where the flow is uniform in both space and time and the profit to be gained at the goal of migration is sufficiently large, the optimal control variables are determined from a system of algebraic equations that can be solved in a cascading manner. Mathematical analysis of the system reveals that the optimal controls are uniquely found and the model is exactly solvable under certain conditions on the functions and parameters, which turn out to be realistic and actually satisfied in experimental fish migration. Identification results of the functional shapes of the functions and the parameters with experimentally observed data of swimming schools of Plecoglossus altivelis (Ayu) validate the present mathematical model from both qualitative and quantitative viewpoints. The present model thus turns out to be consistent with the reality, showing its potential applicability to assessing fish migration in applications.