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The ayu Plecoglossus altivelis (Temminck and Schlegel 1846), an annual and amphidromous fish, is generally distributed in the islands of Japan and along the Asian continental coast. Recently, it has been found in two rivers of northern Vietnam and the Tien Yen River is the southernmost distribution range of this species. Morphology of the ayu in Vietnam has been examined; however, its reproductive biology is poorly known. Therefore, this study attempted to describe the fecundity and the egg size of the ayu from this river. Gonadosomatic index (GSI) of the female ayu (160.0-194.7 mm standard length, SL) was 19.7- 25.9 %. The number of eggs ranged from 33,548 to 45,114. Egg size ranged from 0.1 to 1.5 mm, with an average diameter of 0.8-0.9 mm. The GSI of the male ayu (153.3-194.7 mm SL) was 2.5-8.3 %. The present findings indicate that the ayu in its southernmost distribution region could spawn at least twice a year, and the breeding period occurs between November and February. This study provides reproductive data on the ayu species, thus contributing to the conservation of endangered ayu populations in Vietnam. [ABSTRACT FROM AUTHOR]

Liver X receptors (LXR) are modulators of metabolic processes and inflammation in mammals as nuclear receptors. However, the precise function of LXR in teleosts remains unclear. Here, we characterized a LXR gene (PaLXR) from ayu, Plecoglossus altivelis . The PaLXR transcript was expressed widely in all tissues studied, and changes in expression were observed in tissues and monocytes/macrophages (MO/MΦ) upon infection with the bacterium Edwardsiella ictaluri . PaLXR activation decreased the mRNA expression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL-10 upon E. ictaluri infection, while their expression was increased following the knockdown of PaLXR by siRNA. Moreover, E. ictaluri infection induced the apoptosis of ayu neutrophils and PaLXR activation enhanced the internalization of E. ictaluri -infected apoptotic neutrophils by MO/MΦ (efferocytosis), while PaLXR knockdown led to decreased efferocytosis. Furthermore, PaLXR activation inhibited intracellular bacterial survival during efferocytosis, while PaLXR knockdown enhanced survival. In conclusion, our results indicate that PaLXR plays a role in the modulation of innate immune responses in ayu MO/MФ. [ABSTRACT FROM AUTHOR]

Pseudomonas plecoglossicida is a lethal pathogen of ayu (Plecoglossus altivelis) in Japan and is responsible for substantial economic costs to ayu culture. Previously, we demonstrated the efficacy of phage therapy against P. plecoglossicida infection using two lytic phages (PPpW-3 and PPpW-4) (S. C. Park, I. Shimamura, M. Fukunaga, K. Mori, and T. Nakai, Appl Environ Microbiol 66:1416 -1422, 2000, http://dx.doi.org/10.1128/AEM.66.4.1416-1422.2000; S. C. Park and T. Nakai, Dis Aquat Org 53:33-39, 2003, http://dx.doi.org/10.3354/dao053033). In the present study, the complete genome sequences of these therapeutic P. plecoglossicida phages were determined and analyzed for deleterious factors as therapeutic agents. The genome of PPpW-3 (myovirus) consisted of 43,564 bp with a GC content of 61.1% and 66 predicted open reading frames (ORFs). Approximately half of the genes were similar to the genes of the Escherichia coli phage vB-EcoM-ECO1230-10 (myovirus). The genome of PPpW-4 (podovirus) consisted of 41,386 bp with a GC content of 56.8% and 50 predicted ORFs. More than 70% of the genes were similar to the genes of Pseudomonas fluorescens phage ϕIBB-PF7A and Pseudomonas putida phage ϕ15 (podoviruses). The whole-genome analysis revealed that no known virulence genes were present in PPpW-3 and PPpW-4. An integrase gene was found in PPpW-3, but other factors used for lysogeny were not confirmed. The PCR detection of phage genes in phage-resistant variants provided no evidence of lysogenic activity in PPpW-3 and PPpW-4. We conclude that these two lytic phages qualify as therapeutic agents. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the induction of protective immunity against bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum by warmed water treatment in ayu (Plecoglossus altivelis). Fish were immersed in a live bacterial suspension (107 CFU mL−1) for 30 min and placed in 700 L concrete tanks. The 28 °C warmed water treatment lasted 3 days and began 1, 6, and 24 h after immersion in the live bacterial suspension. A naïve control fish group was immersed in a sterilized modified Cytophaga (MCY) broth instead of the bacterial suspension. Fourteen days after the immersion, agglutination antibody titers against F. psychrophilum were measured by using micro-titer methods. Fish were then exposed to a bacterial bath to infect them with live F. psychrophilum, and cumulative mortality was monitored. Fish treated with warmed water at 1, 6, and 24 h after immersion in the live bacterial suspension had cumulative mortalities of 36%, 30%, and 18%, respectively, all of which were significantly lower than the cumulative mortality of the naïve control fish (90%). Treated fish also showed high antibody titers against F. psychrophilum in agglutination tests. These results demonstrate that warmed water treatment could not only cure BCWD but also immunize the fish against the causative agent F. psychrophilum. [Copyright &y& Elsevier]

Flavobacterium psychrophilum isolates, obtained from ayu, Plecoglossus altivelis, three species of salmonids and two species of cyprinids in Japan, were used in this study. Bacteria were inoculated to serum prepared from ayu or red spotted masu trout (RSMT), Oncorhynchus masou ishikawae, and incubated at 18 °C for 24 h. All isolates ( n = 19) from ayu grew well with a 9- to 116-fold increase of CFU in ayu serum, while CFU decreased markedly in RSMT serum. In contrast, isolates ( n = 17) from fish species other than ayu exhibited no growth in ayu serum, but some isolates from salmonids survived or grew (1.2-23.5 fold increase of CFU) in RSMT serum. The isolates that could not survive or grow in ayu and RSMT sera grew well in both heat-inactivated sera of ayu and RSMT. Experimental infection by intraperitoneal injection showed that ayu isolates examined were all pathogenic to ayu but not to RSMT, while none of the isolates from salmonids and cyprinids were pathogenic to ayu but some showed pathogenicity to RSMT. These results indicate that the in vitro growth ability of F. psychrophilum isolates in fish serum correlates well with their pathogenicity to fish, particularly in ayu. [ABSTRACT FROM AUTHOR]

The occurrence and body size of drifting land-locked Ryukyu-ayu, Plecoglossus altivelis ryukyuensis, larvae were investigated in the San-numata River, Okinawa-jima Island from November 2000 to March 2001. The water temperature in the river fluctuated from 13.8 to 17.9°C during the sampling period. The drifting larvae occurred from mid-December to mid-March with an estimated spawning peak during late November and early December. The notochord length of the drifting larvae ranged from 4.9 to 6.7 mm (5.7 ± 0.3 mm, mean ± SD), and became longer as the spawning months progressed. These results imply that the land-locked population possesses the same maturation attributes as the original amphidromous population. [ABSTRACT FROM AUTHOR]

Female ayu Plecoglossus altivelis were sampled from the Mogami River System, Yamagata Prefecture to investigate the occurrence of multiple spawning that has previously been reported in small rivers. Spawning frequencies of the females were estimated by histological observations of the ovary mainly from the degree of degeneration of postovulatory follicles. In the middle and late part of the spawning period, most females showed characteristics of having spawned two or three times, indicating that multiple spawning is a common phenomenon also in a large river. Mean relative batch fecundity (RBF) and condition factor (without gonads) decreased with the number of spawning batches. Size dependency in the occurrence of the multiple spawning and the RBF values was not observed. These results are similar to those reported in previous studies of ayu from a small river near the Mogami River System, and indicate that the occurrence and properties of multiple spawning are almost the same regardless of the river scale. However, it is possible that the ratios of multiply spawned females may differ due to variations in survival rates during the spawning season. [ABSTRACT FROM AUTHOR]

1. Animals exploiting different resources may nevertheless interact if one species indirectly alters the abundance and distribution of the food of the other. To analyse this indirect effect, we conducted experiments in artificial pools and in the field to investigate the influence of the algivorous fish Plecoglossus altivelis altivelis (known as the ayu) on two species of insectivorous benthic fish, Pseudogobio esocinus esocinus and the goby Gymnogobius petschiliensis. 2. In the pool experiments, algal biomass was not correlated with the number of ayu, but the percentage of blue-green bacteria rose as the number increased. The number of aquatic macroinvertebrates on the upper surface of ceramic tiles placed in the pool bed decreased as the number of ayu increased. 3. Although ayu and the benthic species did not interact directly, the reduction in invertebrate abundance on the upper surface of tiles in the pool reduced the growth rate of the benthic insectivores. 4. In field experiments, the introduction of ayu into habitats with P. esocinus esocinus or G. petschiliensis reduced the growth rate of these benthic fish. In the field experiment that was carried out over 5 years in the G. petschiliensis habitat, the population density of the goby decreased when ayu were stocked. 5. The ayu is a strong interactor or bioengineer in streams, affecting not only benthic algae but also aquatic invertebrates and fishes. We conclude that to predict the outcome of interspecific interactions amongst fishes in streams with high algal production, possible indirect effects must be considered alongside better known direct effects. [ABSTRACT FROM AUTHOR]

Abstract: A rhamnose-binding lectin, named SFL, was isolated from the eggs of ayu (sweet fish, Plecoglossus altivelis) by affinity and ion-exchange chromatographies. SFL revealed 287 amino acid residues with 3 tandemly repeated domains, and contained 8 half-Cys residues in each domain. The lectin was shown to have a highly specific binding affinity to globotriaosylceramide (Gb3) by frontal affinity chromatography using 100 oligosaccharides. SFL was localized in several tissues and serum of both male and female ayu, such as gill, liver, ovary, testis, intestine, stomach, brain, kidney and serum. The lectin agglutinated the spores of the microsporidian Glugea plecoglossi, which is a pathogen of ayu. Although SFL bound to glycoproteins and glycolipids of G. plecoglossi spores, Gb3 could not be detected in either of them. The results suggest that SFL could interact with various glycoconjugates of pathogens to play a role in the adhesion of microorganisms invading in the body. [Copyright &y& Elsevier]

Self-feeding of grouped ayu Plecoglossus altivelis altivelis was examined under an artificial light–dark (LD) cycle and natural day length using a trigger with a photosensitive sensor. In Experiment 1, approximately 15 juvenile fish (mean body weight, 0.6 g) were kept in 60-L glass tanks (four tanks) under LD 12:12 (lighting period 06:00–18:00 hours) and self-feeding and locomotor activities were simultaneously recorded. Self-feeding was detected within one day and feeding activities were strongly synchronized to the LD cycle, with almost strictly diurnal feeding (98.2%). Although locomotor activities in the upper part of the tank were also greatest during the light phase (76.8%), the activity profiles were different from those of self-feeding, suggesting the validity of the photosensitive sensor. In Experiment 2, 25 fish (mean body weight, 15 g) were kept in outdoor 1000-L tanks (four tanks) under natural day length and water temperatures in May, and self-feeding was recorded from mid-August. Stable self-feeding was observed from early September in all the tanks. Nearly all food demands were diurnal, and usually crepuscular. Somatic growth was seen in all tanks. These results demonstrate that the self-feeding system using a photosensitive sensor is applicable for grouped juvenile ayu as small as 0.6 g and adult fish reared under natural conditions. [ABSTRACT FROM AUTHOR]

1. In an experimental flume, we examined the effects of a biomass reduction and alteration of taxonomic composition, because of grazing by the fish Plecoglossus altivelis, on the net biomass accumulation of periphyton. 2. Grazed and ungrazed assemblages with different biomass and taxonomic composition were first prepared in fish enclosures and exclosures, respectively. These assemblages were then set out in the flume and incubated for 2 days under grazing-free conditions to examine (i) the relationship between biomass and biomass accumulation rate and (ii) the effect of taxonomic composition on the relationship between these two. 3. The grazed and ungrazed assemblages were dominated by upright filamentous cyanobacteria and diatoms, respectively. The rate of biomass accumulation decreased with increasing periphyton biomass in both the grazed and ungrazed assemblages, and was lower in the grazed than the ungrazed assemblages at any biomass level. 4. The results showed that the reduction in biomass and the alteration of taxonomic composition due to fish grazing have opposite effects on biomass-specific productivity. Biomass accumulation rate increased in response to biomass reduction, although a shift in dominance from diatoms to upright filamentous cyanobacteria decreased the overall productivity of the periphyton. [ABSTRACT FROM AUTHOR]

Adult ayu Plecoglossus altivelis were sampled from the Nezugaseki River, Yamagata Prefecture to investigate the reproductive parameters and analyze their variations related to multiple spawning. Ovarian histology (mainly based on the occurrence of postovulatory follicles) indicated that female ayu can be divided into four groups, which are considered to correspond with unspawned, once spawned, twice spawned, and three (or more) times spawned individuals. Comprehensive analysis of the ovarian state with field surveys revealed that most of the female ayu achieve second spawning and that third spawning is very common in this river. Mean relative batch fecundity (RBF) for the second, third, and fourth spawning indicated 69, 42, and 22%, respectively, of the value for the first spawning, showing a decline with the number of spawning batches. Mean gonadosomatic index (GSI) values of non-ovulating fish showed a similar decline during the main spawning period (October). Condition factor (without gonads) during autumn also decreased with the number of batches spawned, suggesting that multiple spawning is achieved partly by transfer of body mass nutrients to the ovary. Size dependency in reproductive parameters such as occurrence of the multiple spawning, RBF values, and GSI values of the unspawned fish, was not evident except for GSI values in early September (generally during the early phases of ovarian development), when larger fish had larger GSI. [ABSTRACT FROM AUTHOR]

Abstract: Sweetfish, Plecoglossus altivelis, obtained from 18 rivers in Shizuoka Prefecture were examined for metacercarial infection of 2 flukes, Metagonimus yokogawai and Metagonimus miyatai. The infection rate and density of metacercariae in the fish were higher in eastern and western regions than in central region of the prefecture. After infection of hamsters with metacercariae derived from the scale, 98.7% of the adult worms obtained from the intestine was found to be M. miyatai. Conversely, from infection with metacercariae from the flesh, 90.0% of the worms was M. yokogawai. Since the worms had no exclusivity in the tissues, we conclude that the flukes have location preference with the former primarily preferring the scale, and the latter the flesh. Fish from two rivers located in adjacent areas in the western region had relatively a higher ratio of M. yokogawai in the scale relative to other rivers, suggesting an intraspecific genetic variation due to geographical isolation. On examination of adult worms in the hamster''s intestine, M. yokogawai was mainly located towards the anterior part of the intestine, unlike M. miyatai, suggesting that in mammalian host too, the parasites have site preference. [Copyright &y& Elsevier]

The recent increase in numbers of individuals of a piscivorous bird, the great cormorant Phalacrocorax carbo hanedae, around Lake Biwa has affected the commercial catch of ayu Plecoglossus altivelis altivelis. The food habits of the bird were studied based on 66 stomachs in 1998 and 2001–2002, and a seasonal variation in food contents was observed. The proportion of ayu in stomachs increased after April, and became most dominant during July and August (0.62 in proportion of weight, 0.85 in frequency of occurrence). In contrast, ayu was not found in the stomachs after late October. The increase of ayu in individuals and density in the surface layer of the pelagic zone of the lake during spring was considered as a trigger for the change of the food habits of the birds. The feeding impact of great cormorant on ayu in Lake Biwa was estimated to be approximately 46 t during April to June, and 310 t in July and August. During the main period for the commercial ayu catch (November to the following June), the estimated mass consumed by the bird is much smaller in comparison with the commercial catch. [ABSTRACT FROM AUTHOR]

The self-feeding rhythms of ayu Plecoglossus altivelis altivelis were examined. Individual ayu (mean body weight 40 g) were held in 60-L glass tanks equipped with self-feeders. Six of 14 fish learned self-feeding during the experiment. Under two different light–dark (LD) conditions (16 h:8 h and 8 h:16 h LD), self-feeding was synchronized to the LD cycle, and feeding occurred almost exclusively during the light phase. During exposure to constant light (LL), circadian feeding rhythms were observed. These results indicate self-feeding rhythms in ayu are restricted to the light phase under LD conditions and are controlled by the circadian clock under LL conditions. [ABSTRACT FROM AUTHOR]

A scanning electron microscopic study of the skin and eye of UV-B radiated ayu Plecoglossus altivelis(age 30 days, mean ± s. e. total length: 16·25 ± 0·11 mm) under laboratory condition showed marked changes when compared with the control fish without UV-B radiation. The exposure of the fish to the radiation resulted in the destruction of microridges in the epidermis and exposed neuromast cells of the skin. Domed protrusions were also more common in the skin of UV-B radiated fish than in the control fish. The appearance of mucus in both groups was different. In the control skin the mucus was spread over a wide area whereas in the treated fish the mucus was concentrated in a small area. The anastomozing structures of the microridges of the eyes were lost in UV-B radiated fish and the microridges themselves were fewer in number, fragmented, and aggregated. Mucus cells, prominently visible in the control fish, were distorted in the treated fish. Cell contours were irregular in UV-B radiated fish and cell to cell contacts had been lost in this group. [ABSTRACT FROM AUTHOR]

The reproducibility, mode of inheritance and polymorphism of amplified fragment length polymorphism(AFLP) markers were examined in ayuPlecoglossus altivelis(Salmoniformes: Plecoglossidae). The AFLP markers were highly reproducible, their inheritance following Mendelian expectations. The number of fragments amplified(34–134), polymorphic ratio(0·15–0·78) and average heterozygosity(0·02–0·25) of the AFLP markers showed significant variation among six primer pairs and among ayu populations, including a landlocked Lake-Biwa population, two amphidromous populations( P. a. altivelis) and two Ryukyu-ayu populations( P. a. ryukyuensis). Although AFLP analysis provided similar results in intra-population diversity and relationships among populations to those found by analyses of allozymes, microsatellites and mitochondrial DNA sequences, AFLPs showed higher polymorphisms and hence greater distinction between genetically close populations. [ABSTRACT FROM AUTHOR]

An increasing demand for stocking of hatchery-reared ayu,Plecoglossus altivelis, has aroused concerns about their genetic status which has an effect on their post-stocking performance and the conservation of native biodiversity. Instead of costly analysis, fluctuating asymmetry (FA) was examined to test its suitability as an indirect measure of genetic diversity. Two bilateral traits, pectoral and pelvic fin rays, were targeted, and two wild and four hatchery populations of ayu were sampled for comparison. Frequency of FA in soft-rays was not similar between specimens in both pelvic and pectoral fins. The wild populations did not show FA incidences lower than the hatchery populations, suggesting a considerable degree of environmental stress operating in the wild populations. Comparison between the hatchery populations showed overall increasing FA incidence with the decrease in genetic diversity, although the correlation was not complete in detail. In conclusion, FA can be used as a convenient tool to compare genetic status, but quantified evaluation is rather limited to monitoring changes in the genetic variation within a hatchery population. [ABSTRACT FROM AUTHOR]

Ayu Plecoglossus altivelis including amphidromous and landlocked populations, are known for batch spawning. Unusual clutches at ovulation were observed from rearing stocks that were naturally induced to sexual maturation. Two peaks occurred simultaneously in the frequency distribution of egg size, compared to normal fish, which have clutches with unimodal size distribution. The eggs in the small size class could be fertilized, and small-sized larvae hatched from these eggs. To explain the alteration in egg size through divergence from amphidromous to landlocked populations, the role of batch allocation among oocytes is discussed. [ABSTRACT FROM AUTHOR]

To clarify the feeding habits of tidal mudflat fishes, the gut contents of 29 fish species, collected from unvegetated tidal mudflats in Tokyo Bay, central Honshu, Japan, were examined. Onto- genetic changes in food preference were recognized in 21 species, including several of commercial importance (e.g. Acanthogobius flavimanus, Konosirus punctatus, Mugil cephalus cephalus, Plecoglossus altivelis altivelis, and Sardinella zunasi). In general, larvae and/or juveniles of these species fed mainly on small zooplankton or benthic harpacticoid copepods, later switching to other prey items with growth (e.g. gammaridean amphipods, mysids, polychaetes, detritus, bivalves, and juvenile fishes). A cluster analysis based on dietary overlaps showed that the tidal mudflat fish assemblage comprised six feeding guilds (small benthic and epiphytic crustacean, zooplankton, detritus, mollusc, polychaete, and fish feeders). Of these, small benthic and epiphytic crustacean feeders were the most abundantly represented in the number of species. [ABSTRACT FROM AUTHOR]

To examine the possibility of dietary α-starch in reducing feed costs in a practical diet, α-starch was supplemented at 10, 20, 30 and 40% in a composed diet having the same protein level. The four diets were fed to ayu, Plecoglossus altivelis (initial weight 9.1 g) for 43 days. Growth and feed efficiency increased with the supplement, with values highest in the 30–40% α-starch diet. The level of dietary α-starch did not affect the proximate muscle composition; although the hepatosomatic index was not affected, liver glycogen increased with increasing dietary α-starch. The dietary α-starch did not influence evacuation time from the gut, and was well digested through passage in the gut, mainly between the stomach and the anterior part of the intestine. Ayu have an ability to adapt their metabolism to high dietary α-starch, and can digest 40% or more in a composed diet. Although the muscle lipid content did not change, the fatty acid composition was influenced by dietary starch. With the elevation of dietary starch, a decrease of C18:2n-6 and an increase of C22:6n-3 occurred. These results indicate that at least 40% α-starch can be used in practical diets for ayu. [ABSTRACT FROM AUTHOR]

A mapping referential family (F1) of ayu was produced by crossing a normal diploid male with a homozygous clonal female. A genetic linkage map was constructed using 191 amplified fragment length polymorphism (AFLP) and 4 microsatellite DNA markers. A total of 178 loci were mapped in 36 linkage groups comprising 1659.6 cM, which includes approximately 77.3% to 81.8% of the total genome. As the markers were randomly distributed over the genome, they showed high efficiency for the construction of a wide linkage map. [ABSTRACT FROM AUTHOR]

Metallothionein (MT) has been used widely as a potential molecular marker to detect the deleterious effects of heavy metals in aquatic ecosystem. Here we exposed ayu, Plecoglossus altivelis, to zinc (Zn) and tested the distribution as well as the induction of MT in various tissues such as liver, kidney, intestine and stomach. MT induction was significant in liver tissue, followed by kidney and intestine, whereas no induction was detected in stomach. The gene encoding ayu MT was successfully cloned and characterized. Complete nucleotide sequencing and analysis of the 4.5 kb DNA fragment containing the ayu MT gene revealed that the gene has three exons interrupted by two introns, a 5′-flanking region of about 2.5 kb and about 1.6 kb of 3′-flanking region. In grouper heart and kidney cells, the 2.5 kb promoter containing eight metal responsive elements (MREs), two hepatic nuclear factor 5 responsive elements (HNF5REs) and one cAMP responsive element (CRE) had the highest reporter activity. [Copyright &y& Elsevier]

In the present study, we tested whether the pineal organ of ayu ( Plecoglossus altivelis), an osmerid teleost close relative of salmonids, harbours a circadian oscillator regulating rhythmic melatonin release using flow-through culture. The pineal organ maintained under light/dark cycles released melatonin in a rhythmic fashion with high levels during the dark phase. A circadian rhythm of melatonin release persisted in constant darkness for at least four cycles. Characteristics of the circadian rhythm (free-running period, phase and amplitude) exhibited small variations among cultures when the data was normalized, indicating that this system is sufficient for the analysis of the circadian rhythm both at qualitative and quantitative levels. Six-hour extension of the light phase from the normal onset time of the dark phase or exposure to constant light for 36 or 48 h before transfer to constant darkness significantly inhibited melatonin release. Phase shifts in the circadian rhythm of melatonin release were also observed. Thus, the ayu pineal organ contains all the three essential components of the circadian system (a circadian clock, the photoreceptor responsible for photic entrainment of the clock, and melatonin generating system as an output pathway). This system should provide a useful model for analysing the physiological and molecular basis of the vertebrate circadian system. In addition, further comparative studies using salmonids and related species including ayu will provide some insight into the evolution of the roles of the pineal organ in the vertebrate circadian system. [ABSTRACT FROM AUTHOR]

Ayu (Plecoglossus altivelis) is a teleost whose gonadal development is stimulated by shortened daylength and is a useful model to study the mechanism of photoperiodism. However, localization and characteristics of the photoreceptor that mediates photoperiodism in gonadal development remain to be determined. To identify the photoreceptive molecule that regulates photoperiodic responses, in the present study, we have cloned and characterized the cDNA encoding an opsin gene expressed in the ayu brain, a putative site of the photoreceptor for photoperiodism. The identified opsin was rhodopsin that is identical to the rhodopsin expressed in the retina. Phylogenetic analysis demonstrated that this rhodopsin belongs to the retina-type but not to the pineal-specific rhodopsin group. Genomic polymerase chain reaction (PCR) demonstrated that the ayu rhodopsin gene is intron-less. Southern and Northern blots and reverse-transcription PCR analyses indicate that the same rhodopsin gene is expressed in the retina and the brain but not in the pineal organ of ayu. These results indicate that the rhodospin gene is expressed in the retina and brain and mediates not only visual but also nonvisual functions such as photoperiodism and entrainment of the circadian clock. [ABSTRACT FROM AUTHOR]

The protective effect of Vibrio anguillarum immunization administered by the direct immersion technique in ayu, Plecoglossus altivelis Temminck and Schiegel, was investigated. The activities of phagocytic cells were suppressed at the time of vaccination by previous bath exposures to a cyclophosphamide solution containing a concentration of 500 mg/kg/ml on days 2 and 3 before vaccination. An artificial challenge was carried out 3 weeks after vaccination by bath exposure. The survival rate of the vaccine group pre-treated with cyclophosphamide was 96%. In the group given traditional vaccine only, 73% survived: and in the non-vaccine control group, 10% survived. These results suggest that protective immunity of ayu vaccinated by the direct immersion technique may not implicate the early activities of phagocytic cells. [ABSTRACT FROM AUTHOR]

Temporal variation in foraging group structure of a fish assemblage was examined in a flood-prone stream in southern Hokkaido, Japan. Foraging behaviour was observed underwater for four species which inhabit the water column: ayu, Plecoglossus altivelis, white-spotted charr, Salvelinus leucomaenis, masu salmon, Oncorhynchus masou, and Japanese dace, Tribolodon hakonensis, with each species being categorized into five size classes (species-size group; SSG). Based on foraging behaviour, each SSG of the fish assemblage was classified into one of four foraging groups: algae grazers, drift foragers, benthos-drift foragers, and omnivores, defined as SSG exhibiting similar foraging behaviour. All size classes of ayu, and of charr and salmon were categorized as algae grazers and drift foragers, respectively, throughout the study period. In contrast, size classes of dace were categorized as drift foragers, benthos-drift foragers, or omnivores with the same size classes often assigned to different foraging groups from month to month. Digestive tract contents of the fishes in the four foraging groups reflected their observed foraging behaviour, and foraging groups were therefore regarded as representing trophic groups. Abundance and membership of each foraging group varied in accordance with changes in abundance of SSG due to their growth, immigration, emigration, and/or mortality. Moreover, due to numerical dominance within the assemblage, plasticity in foraging behaviour of small- and medium-sized dace also played a key role in determining variability in the foraging group structure. Relative frequencies of two types of foraging behaviour, algae nipping and benthos foraging, of the small-sized dace were significantly correlated with the level of each resource, whereas no significant relationship was detected between foraging frequencies of the medium-sized dace and either resource. Fluctuations in foraging group structure within this assemblage occurred through niche shifts of some component members and by changes in SSG composition. [ABSTRACT FROM AUTHOR]

Four clonal lines of ayu, Plecoglossus altivelis Temminck — Schlegel, were produced through gynogenesis, mixed before hatching and reared communally. After 10 months, a randomly taken sample was subjected to a standardized shallow-water stressor. Haematocrit, haemoglobin, red blood cells count (RBC) and mean corpuscular volume (MCV) were obtained from stressed and non-stressed fish. DNA fingerprinting was used to confirm the clonal nature of the organisms and to identify the clonal line to which each fish belonged. We observed significant differences between clonal lines mostly in the haematocrit and MCV measured under no-stress conditions. Such differences are suggested to represent mainly genetic variance, on account of the common environment provided to all the experimental groups. The stress response ratio was lower than expected, mainly due to some unexpectedly high non-stress values. Heritability values (h2) were medium to high for the no-stress measurements (mean 0.238) and very low or zero for the stressed groups' traits (excepting one high value of 0.484). We conclude that the use of communally reared clonal lines represents a good tool for the characterization of the physiological traits, thus allowing for their utilization as genetic selection criteria. [ABSTRACT FROM AUTHOR]

This article presents a study on the occurrence of multiple spawning in the wild amphidromous type ayu. Adult ayu were collected from the Nezugaseki River in Yamagata, Japan by cast net or by electrofishing during autumn of 2001. The collected fish were killed with tricaine methanesulfonate and sectioned. Female ayu were divided into three groups by the occurrence of post ovulatory follicles. The results demonstrate the occurrence of multiple spawning in wild amphidromous type ayu, and also indicate that multiple spawning is a common phenomenon in the Nezugaseki River.