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Thelazia callipaeda (Nematoda: Spirurida: Thelaziidae) parasitizes the eyes of dogs, cats, humans, and various wild mammals, and is transmitted by drosophilid flies. In Japan, T. callipaeda is considered an emerging parasite that has expanded its endemic region northward. However, reports of its detection in mammals other than domestic animals and humans are scarce. This study reports the detection of T. callipaeda in Japanese red fox (Vulpes vulpes japonica), masked palm civet (Paguma larvata) , Japanese badger (Meles anakuma), Japanese black bear (Ursus thibetanus japonicus) , raccoon (Procyon lotor) , Japanese raccoon dog (Nyctereutes viverrinus), domestic dog (Canis lupus familiaris), domestic cat (Felis silvestris catus), and human. Of these, the Japanese red fox, masked palm civet, Japanese badger, and Japanese black bear have been reported as novel host records. Sequence analysis of the cytochrome c oxidase subunit I gene of T. callipaeda revealed two unique lineages specific to Japan, with no regional or host species differences. These results suggest a wide host range for T. callipaeda, highlighting the significant role of wildlife as a reservoir for this parasite in Japan. [Display omitted] • Thelazia callipaeda was found in several wild mammals, humans, domestic cats and dogs. • Masked palm civet, Japanese black bear, badger, and red fox are novel host records. • Sequence analysis revealed two unique lineages, with no regional or host differences. [ABSTRACT FROM AUTHOR]

Damming of streams and rivers alters downstream ecosystem processes, and understanding its effects is essential in managing forested mountain streams. This study examined the effects of dams with a reservoir on organic matter decomposition and its seasonality in two neighbouring mountain streams over five seasons. The cotton‐strip assay and measurement of tensile strength loss were used to evaluate decomposition rates. In addition, the environmental factors, such as water level, water temperature, inorganic nitrogen concentrations and contribution of macro invertebrates were measured. The dams with a reservoir lowered decomposition rates downstream compared to upstream and unregulated sites, in all seasons. The decomposition rates also varied by season at all sites, with higher rates in summer and lowest in winter, and the seasonal variation was larger than the effects by the reservoirs in both streams. Seasonal variation in decomposition rates coincided with water temperature variation, suggesting strong influence of water temperature. However, the temperature differences did not explain the effects of reservoirs because water temperature was always higher at downstream sites. The downstream sites had lower nitrate concentrations and contribution of macroinvertebrates, and these factors may have greater effects than water temperature. Thus, damming of streams may lower the decomposition rates at downstream sites due to altered nutrient and biological effects. However, seasonal variation in water temperature may have more pronounced effects, resulting in greater seasonal variation than the difference among sites. [ABSTRACT FROM AUTHOR]

Dissemination of extend-spectrum cephalosporin (ESC)-resistant Salmonella, especially extended-spectrum ß-lactamase (ESBL)-producing Salmonella, is a concern worldwide. Here, we assessed Salmonella carriage by food workers in Japan to clarify the prevalence of ESC-resistant Salmonella harboring blaCTX-M. We then characterized the genetic features, such as transposable elements, of blaCTX-M-harboring plasmids using whole-genome sequencing. A total of 145,220 stool samples were collected from food workers, including cooks and servers from several restaurants as well as food factory workers, from January-October 2017. Isolated salmonellae were subjected to antimicrobial susceptibility testing (disk diffusion method), and whole-genome sequencing was performed for Salmonella strains harboring blaCTX-M. Overall, 164 Salmonella isolates (0.113%) were recovered from 164 samples, from which we estimated that at least 0.113% (95% confidence interval (CI): 0.096%-0.132%) of food workers may carry Salmonella. Based on this estimation, 3,473 (95% CI: 2,962-4,047) individuals among the 3,075,330 Japanese food workers are likely to carry Salmonella. Of the 158 culturable isolates, seven showed resistance to ESCs: three isolates harbored blaCMY-2 and produced AmpC ß-lactamase, while four ESBL-producing isolates harbored blaCTX-M-14 (n = 1, Salmonella enterica serovar Senftenberg) or blaCTX-M-15 (n = 3, S. enterica serovar Haardt). blaCTX-M-15 was chromosomally-located in the S. Haardt isolates, which also contained ISEcp1, while the S. Senftenberg isolate contained an IncFIA(HI1)/IncHI1A/IncHI1B(R27) hybrid plasmid carrying blaCTX-M-14 along with ISEcp1. This study indicates that food workers may be a reservoir of ESBL-producing Salmonella and associated genes. Thus, these workers may contribute to the spread of blaCTX-M via plasmids or mobile genetic elements such as ISEcp1. [ABSTRACT FROM AUTHOR]

Natural reservoirs of Escherichia albertii remain unclear. In this study, we detected E. albertii by PCR in 248 (57.7%) of 430 raccoons from Osaka, Japan, and isolated 143 E. albertii strains from the 62 PCR-positive samples. These data indicate that raccoons could be a natural reservoir of E. albertii in Japan. [ABSTRACT FROM AUTHOR]

The potential role of wild boars as a source of erysipelas infection was investigated. An ELISA test of wild boar serum samples from 41 prefectures in Japan revealed that proportions of the Erysipelothrix rhusiopathiae‐positive samples were very high in all the prefectures, and the mean positive rate was 95.6% (1312/1372). Serovars of E. rhusiopathiae isolates from wild boars were similar to those of previously reported swine isolates, and all serovar isolates tested were found to be pathogenic to mice. These results suggest that wild boars in Japan constitute a reservoir of E. rhusiopathiae and may pose risks to other animals. [ABSTRACT FROM AUTHOR]

Escherichia albertii is an emerging enteric bacterial pathogen causing watery diarrhea, abdominal distension, vomiting and fever in humans. E. albertii has caused many foodborne outbreaks in Japan and was also reported in other countries worldwide. However, the important animal reservoirs of this pathogen are still largely unknown, impeding us to combat this emerging pathogen. Recently, we reported that wild raccoons (Procyon lotor) and broiler chickens are significant reservoirs of E. albertii in Japan and the U.S., respectively. Here, we performed a longitudinal surveillance to monitor prevalence of E. albertii in wild raccoons in the U.S. and conducted comprehensive comparative analyses of the E. albertii of different origins. A total of 289 fecal swab samples were collected from wild raccoons in Tennessee and Kentucky in the U.S. (2018–2020). Approximately 26% (74/289) of the raccoons examined were PCR-positive for E. albertii and eventually 22 E. albertii isolates were obtained. PFGE analysis showed the U.S. raccoon E. albertii were phylogenetically distant even though the corresponding raccoons were captured from a small area. Unlike the high prevalence of multidrug resistance (83%) observed in previous chicken E. albertii survey, antibiotic resistance was rarely observed in all the U.S. raccoon and 22 Japan raccoon strains with only one Japan strain displaying multidrug resistance (2%). Whole genome sequencing of 54 diverse E. albertii strains and subsequent comparative genomics analysis revealed unique clusters that displayed close evolutionary relationships and similar virulence gene profiles among the strains of different origins in terms of geographical locations (e.g., U.S. and Japan) and hosts (raccoon, chicken, swine, and human). Challenge experiment demonstrated raccoon E. albertii strains could successfully colonize in the chicken intestine at 3 and 8 days postinfection. A pilot environmental survey further showed all the four tested water samples from Tennessee river were E. albertii -positive; two different E. albertii strains, isolated from a single water sample, showed close relationships to those of human origin. Together, the findings from this study provide new insights into the ecology, evolution, and pathobiology of E. albertii, and underscore the need to control the emerging E. albertii in a complex ecosystem using One Health approach. [ABSTRACT FROM AUTHOR]

A unique method to trace the source of “difficult-to-settle fine particles,” which are a causative factor of long-term turbidity in reservoirs was developed. This method is characterized by cluster analysis of XRD (X-ray diffraction) data and homology comparison of major component compositions between “difficult-to-settle fine particles” contained in landslide soil samples taken from the upstream of a dam, and suspended “long-term turbid water particles” in the reservoir, which is subject to long-term turbidity. The experiment carried out to validate the proposed method, demonstrated a high possibility of being able to make an almost identical match between “difficult-to-settle fine particles” taken from landslide soils at specific locations and “long-term turbid water particles” taken from a reservoir. This method has the potential to determine substances causing long-term turbidity and the locations of soils from which those substances came. Appropriate countermeasures can then be taken at those specific locations. [Copyright &y& Elsevier]

Purpose: In the reservoir created in the reclaimed land in Isahaya Bay, Japan, Microcystis aeruginosa, which produces microcystins (MCs), bloomed every year, and the water with high levels of MCs in the reservoir has been often drained to Isahaya Bay to adjust the water level. The principal aims of this study are to clarify the water conditions suitable for blooming of M. aeruginosa in the reservoir, to follow the amount of distribution of MCs inside and outside the reservoir, and to discuss how blooming of M. aeruginosa is controlled in the reservoir and how MCs produced by Microcystis spread or accumulate in the aquatic environment. Method: We monitored the water quality (temperature, salinity, dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus) in the reservoir with seasonal blooming of microalgae including phytoplankton and M. aeruginosa using the concentrations of chlorophyll α and MCs, respectively, and collected the surface sediment in the reservoir and the bay to determine the MC content using the ELISA method. Result: M. aeruginosa bloomed in extremely low DIN conditions of the water in warm seasons (spring and late summer to autumn). The year-mean standing stock of MCs was approximately 34.5 kg in the water and 8.4 kg in the surface sediment in the reservoir. Approximately 64.5 kg of MCs was discharged with the effluent to the bay in a year. Conclusion: Since a large amount of MCs always suspends in the water in the reservoir and it has been discharged to the bay, suspension-feeding animals are exposed most seriously to the high levels of MCs occurring in these areas. We need to pay attention to the danger of widespread dispersal of MCs and biological concentration of MCs by fish and clam inside and outside the reservoir. [ABSTRACT FROM AUTHOR]

The article presents a study that determines that genetic effects of habitat fragmentation in three species of aquatic insects in north-eastern Japan. It suggests that intermediate dispersers like those at equilibrium between migration and genetic drift within drainages, are more likely to be affected by fragmentation. It concludes that intermediate dispersers could be used as indicator species in studies aimed at detecting the effects of distance between habitat fragments.

The article presents a study on the isolation and characterization of leptospires from raccoons in Japan. This study investigated whether raccoons in Japan carried leptospires in their kidneys. Seventy-one raccoons were captured in Kanagawa Prefecture and 53 raccoons were captured at a zoological park in Nagasaki Prefecture, both in Japan, and leptospira was isolated from 2 of the 71 raccoons and 33 of the 53 raccoons. Anti-leptospira antibodies were found in 16 of 124 raccoons (12.9 %) in Kanagawa and 33 of 53 (62.3 %) raccoons in Nagasaki. Although the claim that raccoons carried leptopires in their kidney at the time imported, it is still believed that imported animals are reservoir animals of leptospires in Japan.

A new fractionation method of silica was developed in order to investigate its behavior in reservoirs. The method included separation of dissolved and particulate fractions, acid extraction, mild alkali extraction, and alkali fusion. The fraction types were dissolved silica (SiD), adsorbed silica (SiAd), amorphous silica (SiAm), and crystalline silica (SiC). Samples were taken from two reservoirs, Iwaya and Kawabe, in the Kiso River in Japan. The inorganic silica (SiAd and SiC) concentrations showed good correlations with the Fe and Al concentrations. The biogenic silica concentration was the difference between total SiAm and Al-bound SiAm. In the deep Iwaya Reservoir, inorganic particulate silica derived from silt and clay was transported from the riverine zone to a deep layer of the lacustrine zone. In the shallow Kawabe Reservoir, biogenic silica increased longitudinally with the growth of diatoms. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms are continuously formed in water systems such as reservoirs and lakes around the world. Geosmin and 2-methylisoborneol (2-MIB) produced by some species of cyanobacteria have caused odor problems in the drinking water of the Sanbe Reservoir in Japan. Field observations were conducted for four years (2015–2019) to investigate the cause of this musty odor. It was found that geosmin was produced by Dolichospermum crassum and Dolichospermum planctonicum (cyanobacteria), and 2-MIB was due to Pseudanabaena sp. and Aphanizomenon cf. flos-aquae (cyanobacteria). Changes in water temperature and pH caused by rainfall were correlated with changes in the concentration of geosmin and 2-MIB. In particular, geosmin and 2-MIB tended to occur under low rainfall conditions. When there was low rainfall, the reservoir changed to an alkaline state because the phytoplankton consumed CO2 for photosynthesis. In an alkaline reservoir, dissolved inorganic carbon mainly existed in the form of bicarbonate (HCO3−). Thus, the results suggest that under such conditions in reservoirs, cyanobacteria grew easily because they could use both CO2 and HCO3− for photosynthesis. Specifically, our study suggests that in order for the musty odor problem in the reservoir to be solved, it is important that the pH of the reservoir be controlled. [ABSTRACT FROM AUTHOR]

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediments to water columns, which may contribute to the long-term contamination of aquatic products. This study systematically investigated the 137 Cs activities of sediment-pore water, providing a direct evidence of the remobilisation of bioavailable 137 Cs from sediments in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. We observed that the dissolved 137 Cs activity concentration of pore water (3.0-65.8 Bq L -1 ) was one to two orders of magnitude higher than that of reservoir water. Moreover, the distribution coefficient (K d ) values for the 137 Cs of sediment-pore water (2.6-14 × 10 3  L kg -1 ) decreased with depth. The K d values were significantly and negatively correlated with the concentration of the major 137 Cs competing cation NH 4 + . Our results strongly indicate a competitive ion exchange process between 137 Cs and NH 4 + via a highly selective interaction with the frayed edge sites of phyllosilicate minerals, which is the major reason for the variability of K d values of sediment-pore water, even in the Fukushima case. Additionally, the sediment accumulation rates were relatively high, and the annual depositional rate of exchangeable 137 Cs is still continuously supplied from the catchment covered by mountainous forests, and reservoir sediments are a long-term important source of bioavailable 137 Cs from the sediment to the overlying water. This finding indicates that even after 10 years since the FDNPP accident, the bioavailable 137 Cs is still continuously supplied from the catchment covered by mountainous forests, and reservoir sediments are a long-term important source of bioavailable 137 Cs in the riverine system. Our findings provide important parameter values for mid- and long-term assessments of the radiation impact of radionuclide discharges to freshwater environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Investigates the seasonal fluctuation of Chrysochromulina parva in four ponds and lakes in the Kinki district in Japan. Distinct feature of Chrysochromulina parva; Effectiveness of Evans blue staining in determining cell viability; Population density of Chrysochromulina parva.

The article focuses on one study which attempts to detect leptospiral DNA in the kidneys of wild boars and deer using polymerase chain reaction (PCR). The detection, accordingly, is for the purpose of assessing the potential role of these animals as reservoirs of leptospires throughout Japan. Kidney tissues from wild boars and deer were examined during the study. Methods such as DNA extraction and data collection were also conducted. Results revealed that Leptospiral flaB was detectable in the kidneys of wild boars. They stressed the fact that wild boars do act as reservoir animals of leptospires in many areas in Japan.

Because of their large mobility and high bioavailability, it is necessary to elucidate the origins and dynamics of dissolved radionuclides in river and reservoir systems to assess the transfer of those radionuclides from water to crops and aquatic organisms. Elution from contaminated reservoir sediments, a potential source of dissolved radionuclides, presents a long-term concern, particularly for long-lived radionuclides. In this study, we systematically investigated caesium-137 ( 137 Cs) concentrations using a time-series suite of input and output water samples collected from 2014 to 2019 from the Ogaki Dam Reservoir, which has a catchment with a high 137 Cs inventory due to the Fukushima Dai-ichi Nuclear Power Plant accident. The results of our study showed that dissolved 137 Cs concentration was significantly higher in the output water than that in the main input water, and that the effective ecological half-life of dissolved 137 Cs in the output water was longer than in the main input water. We quantitatively evaluated the mass balance of dissolved 137 Cs in the reservoir to elucidate how much dissolved 137 Cs from the rivers and production from reservoir sediments contribute to 137 Cs in the reservoir output. The annual output of dissolved 137 Cs was significantly higher than the total input of dissolved 137 Cs, with approximately 32%-40% of the dissolved 137 Cs in the output water presumably being produced from reservoir sediments. Consequently, the estimated dissolved 137 Cs fluxes from reservoir sediments to overlying water were 0.57-1.3 × 10 4  Bq m -2 y -1 . This implies that approximately 0.04%-0.09% of 137 Cs accumulated in the sediments was released through elution to the overlying water each year. Reservoir sediments containing high 137 Cs levels may thus become even more important as sources of bioavailable dissolved 137 Cs in the future., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Dissemination of extended-spectrum-cephalosporin (ESC)-resistant Salmonella , especially extended-spectrum-β-lactamase (ESBL)-producing Salmonella , is a concern worldwide. Here, we assessed Salmonella carriage by food workers in Japan to clarify the prevalence of ESC-resistant Salmonella harboring bla CTX-M We then characterized the genetic features, such as transposable elements, of bla CTX-M -harboring plasmids using whole-genome sequencing. A total of 145,220 stool samples were collected from food workers, including cooks and servers from several restaurants, as well as food factory workers, from January to October 2017. Isolated salmonellae were subjected to antimicrobial susceptibility testing (disk diffusion method), and whole-genome sequencing was performed for Salmonella strains harboring bla CTX-M Overall, 164 Salmonella isolates (0.113%) were recovered from 164 samples, from which we estimated that at least 0.113% (95% confidence interval [CI]: 0.096 to 0.132%) of food workers may carry Salmonella Based on this estimation, 3,473 (95% CI = 2,962 to 4,047) individuals among the 3,075,330 Japanese food workers are likely to carry Salmonella Of the 158 culturable isolates, seven showed resistance to ESCs: three isolates harbored bla CMY-2 and produced AmpC β-lactamase, while four ESBL-producing isolates harbored bla CTX-M-14 ( n  = 1, Salmonella enterica serovar Senftenberg) or bla CTX-M-15 ( n  = 3, S. enterica This study indicates that food workers may be a reservoir of ESBL-producing bla CTX-M-15 was chromosomally located in the S Haardt isolates, which also contained IS Ecp1 , while the S Senftenberg isolate contained an IncFIA(HI1)/IncHI1A/IncHI1B(R27) hybrid plasmid carrying bla carriage among food handlers in Japan. Overall, 164 of 145,220 fecal samples (0.113%) were positive for CTX-M-14 along with IS Ecp1 This study indicates that food workers may be a reservoir of ESBL-producing Salmonella and associated genes. Thus, these workers may contribute to the spread of bla , regardless of whether they were located on the chromosome or on a plasmid. Our findings suggest that food workers may be a reservoir of ESBL-producing strains and could contribute to the spread of resistance genes from farm-derived CTX-M via plasmids or mobile genetic elements such as IS Ecp1 IMPORTANCE Antimicrobial-resistant Salmonella bacteria arise in farm environments through imprudent use of antimicrobials. Subsequently, these antimicrobial-resistant strains, such as extended-spectrum-β-lactamase (ESBL)-producing Salmonella , may be transmitted to humans via food animal-derived products. Here, we examined Salmonella carriage among food handlers in Japan. Overall, 164 of 145,220 fecal samples (0.113%) were positive for Salmonella Among the 158 tested isolates, four were identified as ESBL-producing isolates carrying ESBL determinants bla CTX-M-15 or bla CTX-M-14 In all cases, the genes coexisted with IS Ecp1 , regardless of whether they were located on the chromosome or on a plasmid. Our findings suggest that food workers may be a reservoir of ESBL-producing strains and could contribute to the spread of resistance genes from farm-derived Salmonella to other bacterial species present in the human gut., (Copyright © 2020 American Society for Microbiology.)

Natural reservoirs of Escherichia albertii remain unclear. In this study, we detected E. albertii by PCR in 248 (57.7%) of 430 raccoons from Osaka, Japan, and isolated 143 E. albertii strains from the 62 PCR-positive samples. These data indicate that raccoons could be a natural reservoir of E. albertii in Japan.

To understand the transfer of radiocesium ( 137 Cs) in inside of deciduous trees, changes in 137 Cs activity concentrations, primarily derived from the Fukushima accident in March 2011, were observed in the upper parts of a Japanese flowering cherry tree (Prunus x yedoensis cv. Somei-Yoshino) between 2015 and 2018. The sampling of the foliar parts occurred over the entire leaf life span from winter bud to litterfall and those of the branches were distinguished based on emergence years (2017, 2016, 2015, 2014-2011, and 2010/before). First, every tissue demonstrated a clear seasonal variation in 137 Cs activity concentration. Second, a synchrony of seasonal variations in 137 Cs activity concentration with those in the biological analogue of K concentration was observed in foliar parts during their growth season, but not in branches nor during the other seasons. With respect to the timing of changes in each tissue with tree phenology, it is possible that K and 137 Cs alternate between leaves and branches via the same translocation mechanisms. The resorption efficiencies (i.e., 1 - [the concentrations in the last litterfall]/[the maximum concentrations in green leaves]) of K and 137 Cs were 76% and 46% in average, respectively. In addition, both leaf buds and branches played an important role as reservoirs during dormancy. The buds storage ratio before and after bud burst (i.e., [the inventories in buds at the end of defoliation]/[those before and after bud burst]) for K were 0.57 and 0.10 in median, respectively, and those for and 137 Cs were 1.14 and 0.14 in median, respectively. Consequently, the transfer of 137 Cs in inside of trees was still visible seven years after deposition, even though the annual reduction in 137 Cs activity concentration was apparent in each tissue., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The source and routes of diarrheagenic Escherichia coli (DEC) remain poorly understood. To investigate the involvement of domestic animals in the dissemination of DEC, the prevalence of DEC in foods and fecal specimens from cattle, pigs, chickens, healthy carriers, and patients in Osaka and Hyogo, Japan was investigated using a multiplex real-time Polymerase Chain Reaction assay. The most abundant virulence genes were astA and eae, which had a prevalence 46.8% and 27.4%, respectively. Additionally, stx1 (26.6%) and stx2 (45.9%) were prevalent in cattle feces, while est (8.5%) and elt (7.6%) were prevalent in pig feces. afaB was the second-most prevalent gene in patients and healthy carriers, and it had detection rates of 5.1% and 8.1%, respectively. In contrast, afaB was not detected in animal feces or foods, except for three porcine fecal samples. The aggR gene was more prevalent in humans than in foods or animal feces. Both Shiga toxin-producing E. coli and atypical enteropathogenic E. coli carried by cattle may be sources for diarrheal diseases in humans. Pigs may be a source for human enterotoxigenic E. coli infections, whereas humans are expected to be the reservoir for diffusely adhering E. coli, enteroaggregative E. coli, and enteroinvasive E. coli.

Freshwater cyanobacteria produce highly toxic substances such as microcystins (MCs), and water containing MCs is often discharged to downstream and coastal areas. We conducted field monitoring in Isahaya Bay to clarify the short-term dynamics of MCs discharged from a reservoir following a cyanobacteria bloom in the warm season. MCs were detected in the seawater of the bay (max. 0.10 μg L(-1)), and were deposited on the sea floor, with the MC content of the surface sediment increasing by approximately five times (0.11±0.077-0.53±0.15 μg kgww(-1), mean±SD) at the four stations near the reservoir drainage gate before and after the discharge. The MCs was then transported from the mouth of the bay by tidal currents during the period of the study. Therefore, the MCs were moved away from the closed water area where the cyanobacteria blooms, and spread throughout the coastal area., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This study introduces the collated results regarding the occurrence of freshwater red tide, the associated deterioration of water qualityand the performance of countermeasures based on a survey of freshwater red tide conducted from 1992 to 1993. It also reports the results of an examination of the characteristic of reservoirs in which freshwater red tide occurs and control factors for occurrence according to multivariate analysis. Based on these results, a freshwater red tide occurrence prediction model was constructed using discriminant analysis, and this study further reports the results of applying this modelto dams under construction. [ABSTRACT FROM AUTHOR]

The distribution and biomass of Peridinium bipes f. occultatum were observed in the autumns of 1991, 1992 and 1994 at the head of the Shorenji Dam reservoir (Mie prefecture, Japan). Summarizing observationsand some other information, we discussed processes related to the accumulation of Peridinium biomass. In the study area, biomass of Peridinium increased at a similar rate to growth day by day, and roughly 2/3 of the daily maximum biomass fluctuated in a given day. The horizontal 'import' and 'export' of Peridinium biomass by flows mainly change the biomass of red tide at the upstream end of the reservoir. Flowcontrol in the reservoir, as well as growth control, will also be important in suppressing freshwater red tide. [ABSTRACT FROM AUTHOR]