Database of fish fauna collected from river channels on alluvial fans in the Kofu Basin, central Japan

Biodiversity Data Journal 13: e159810 doi: 10.3897/BDJ.13.e159810 Data Paper Database of fish fauna collected from river channels on alluvial fans in the Kofu Basin, central Japan Rei Itsukushima , Kazuaki Ohtsuki , Kota Tawa , Tatsuro Sato , Kazuki Karasawa ‡ Kyushu University, Fukuoka, Japan § Kyushu Institute of Technology, Kitakyushu, Japan | University of Yamanashi, Kofu, Japan ¶ National Institute for Environmental Studies, Tsukuba, Japan Corresponding author: Rei Itsukushima ([email protected]) Academic editor: Yahui Zhao Received: 21 May 2025 | Accepted: 16 Sep 2025 | Published: 07 Oct 2025 Citation: Itsukushima R, Ohtsuki K, Tawa K, Sato T, Karasawa K (2025) Database of fish fauna collected from river channels on alluvial fans in the Kofu Basin, central Japan. Biodiversity Data Journal 13: e159810. https://doi.org/10.3897/BDJ.13.e159810 Abstract Background Alluvial fans, located near mountainous regions, are characterised by substantial sediment supply, large variations in flow and significant disturbances. The river channels on alluvial fans support a distinct biological community compared to those on alluvial plains. In Japan, gravel extraction and riverbed dredging to maintain flood discharge capacity were frequently carried out during the rapid economic growth period of the 1960s, leading to significant human impact on these rivers. As a result of frequent disturbances, the fish communities in these rivers tend to be less diverse. Furthermore, research on river channels in alluvial fans is limited compared to that on alluvial plains, resulting in a lack of detailed information on these ecosystems. Consequently, efforts for ecosystem conservation and restoration in these environments are insufficient. ‡,§ | ¶ ‡ | © Itsukushima R et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. New information A fish survey was conducted at a total of 26 sites across four river channels on alluvial fans, each with distinct geological characteristics. The results revealed the presence of 2,265 individuals belonging to 15 species and one genus (only the genus could be identified) within seven families. Amongst the confirmed species were Misgurnus anguillicaudatus (Cantor, 1842), Oncorhynchus masou ishikawae (Jordan and McGregor, 1925) and Cottus pollux Günther, 1873, all of which are listed in the local Red Data Book, highlighting the presence of rare species even in river channels on alluvial fans impacted by human activity. Furthermore, non-native species were found only at a single site in the upstream section, where four individuals of Oncorhynchus mykiss (Walbaum, 1792) were collected. The survey indicated that species diversity and fish species composition varied across the different rivers, suggesting that various factors, such as watershed geology, geomorphological processes and anthropogenic influences, contribute to differences in fish community structure. Keywords anthropogenic impact, ichthyofauna, watershed geology, natural disasters Introduction Alluvial fans are the most widespread depositional landforms, occurring along the margins of long-standing highland areas or around actively subsiding continental basins, spanning a wide range of structural and climatic environments (Ventra and Clarke 2018). Rivers flowing through alluvial fans exhibit unique channel characteristics, such as diverse channel migrations and braided river systems influenced by sediment deposition, making them distinct from other river systems (Blair and Mcpherson 1994, Liu et al. 2024). The river channels on alluvial fans, located near mountainous regions, are characterised by substantial sediment supply, large fluctuations in flow and significant disturbances, which contribute to the formation of a distinct biological community compared to rivers in the alluvial plains. In New Zealand, the genetic structure of Galaxias vulgaris Stokell, 1949, differs between alluvial fan rivers and other river systems. In particular, in the braided river channels of alluvial fans, the genetic divergence is shallower due to the instability of the channels (Wallis et al. 2008). Additionally, even within the alluvial fan, the fish communities in the main river and the floodplain are distinct, with the spring-fed areas at the fan's edge acting as hotspots. It has been noted that the diversity of the main river is relatively low (Hirai 1974). In alluvial fans, the large amount of sediment supplied from mountainous areas leads to the frequent deposition of sediment within the riverbed (Ishikawa 1986) and riverbed dredging is regularly carried out to maintain the river’s flood discharge capacity (Ikeda et al. 2017). Additionally, during Japan's rapid economic growth in the 1960s, there was a 2Itsukushima R et al significant demand for gravel and large-scale sediment extraction was conducted in river channels on alluvial fans (Kayaba 2000, Watanabe et al. 2006). Such dredging activities, which involve alterations to the channel morphology, typically lead to habitat modifications, resulting in a decline in biodiversity. This has been reported in both alluvial fan rivers and other river systems (Kondolf 1994, Ellery and McCarthy 2002). Although river channels on alluvial fans are strongly influenced by both natural disturbances and anthropogenic impacts, the fish communities in these rivers are potentially less diverse. Consequently, compared to alluvial plains, there are fewer studies on alluvial fans and information remains scarce. As a result, progress in ecosystem conservation and restoration in these environments is limited. This study was conducted to clarify the fish community structure in rivers flowing through small alluvial fans, where species diversity is believed to be reduced due to the natural disturbances associated with abundant sediment supply and anthropogenic riverbed dredging for flood control measures. Sampling methods Description:The study area is located within the Fuji River Basin, Japan (Fig. 1). Fish surveys were conducted using an electrofisher (Smith-Root Model 12-A, Smith-Root Inc., Vancouver, WA, U.S.A.) at each study site. Fish temporarily immobilised by electric current were collected using dip nets, identified to species and subsequently released at their respective capture sites. The survey was conducted between 22 October and 29 October 2024. Sampling description:Fish surveys were conducted using an electrofisher (Smith-Root Model 12-A, Smith-Root Inc., Vancouver, WA, U.S.A.) at each study site. The survey length was generally set to one reach (approximately ten times the width of the river). The collected fish species were identified on-site and released immediately. Additionally, the Figure 1. Location of the study sites. The study focused on 26 sites within the Kofu Basin.  Database of fish fauna collected from river channels on alluvial fans in ... 3 wet weight of each species was measured at each site. In this research, we recorded 2,265 individuals which were identified on-site and in the laboratory according to Kawanabe and Mizuno (1989) and Seno (2007). Geographic coverage Description:The study area is located within the Fuji River Basin, which flows through the Fossa Magna zone, the boundary between the ichthyofaunas of south-western and north-eastern Japan (Itsukushima 2019). The study sites consist of 26 locations across four tributaries – Midai River, Ara River, Kane River and Omo River – within the Kofu Basin, each exhibiting distinct watershed characteristics. All of these rivers form alluvial fans and the study focused on locations with similar riverbed gradients. These four rivers are formed by different geological substrates: the Midai River by basalt, the Ara River by granite and rhyolite, the Kane River by diorite and the Omo River by granodiorite. Of the 26 study sites, 17 have undergone recent riverbed dredging, while nine have not. Coordinates:35.57553 and 35.73237 Latitude; 138.3801 and 138.7913 Longitude. Taxonomic coverage Description:The survey results revealed that a total of 15 species and one genus (only the genus could be identified) within seven families were observed, with 2,265 individuals recorded across the 26 sites. The location with the highest number of species was downstream of the Kane River, where 10 species were found. The location with the highest number of individuals was in the middle reaches of the Kane River, with 260 individuals recorded. In contrast, no fish species were captured in the upper reaches of the Midai River. The species with the highest number of individuals captured was Rhinogobius sp., with 818 individuals recorded across 20 sites. This was followed by Rhynchocypris lagowskii steindachneri Sauvage, 1883, with 450 individuals captured across 21 sites. The taxonomic orders observed were Cypriniformes (9 species), Perciformes (2 species), Salmoniformes (2 species), Siluriformes (2 species) and Osmeriformes (1 species) (Fig. 2). At the family level, the following families were represented: Cyprinidae (9 species), Cobitidae (2 species), Siluridae (1 species), Gobiidae (1 species), Amblycipitidae (1 species), Cottidae (1 species) and Osmeridae (1 species) (Fig. 3). Amongst the collected fish species, those listed in the Yamanashi Prefecture Red Data Book (2018) as species at risk of extinction include Misgurnus anguillicaudatus, which is categorised as Data Deficient (DD), Oncorhynchus masou ishikawae, which is listed as a Threatened Local Population (LP) and Cottus pollux, which is categorised as Noteworthy Species (N). However, Oncorhynchus masou ishikawae has been subject to extensive transplantation (Kitanishi et al. 2017) and stocking, which facilitates hybridisation with Oncorhynchus masou masou (Yamazaki et al. 2005), raising the possibility that it may not 4Itsukushima R et al be a native population. In the Ministry of the Environment's National Red Data Book (2020), in addition to the aforementioned species, Liobagrus reini HilGündorf, 1878 is listed as Vulnerable (VU). Furthermore, as an invasive species, Oncorhynchus mykiss was captured in the uppermost reaches of the Kane River, with four individuals recorded. Figure 2. Taxonomic Coverage (by order).  Figure 3. Taxonomic Coverage (by family).  Database of fish fauna collected from river channels on alluvial fans in ... 5 Taxa included: Rank Scientific Name family Salmonidae subspecies Oncorhynchus masou ishikawae (Jordan and McGregor, 1925) species Oncorhynchus mykiss (Walbaum, 1792) family Cyprinidae subspecies Rhynchocypris lagowskii steindachneri Sauvage, 1883 species Opsariichthys platypus (Temminck et Schlegel, 1846) species Nipponocypris temminckii (Temminck et Schlegel, 1846) species Pseudogobio polystictus Tominaga and Kawase, 2019 species Pseudorasbora parva (Temminck et Schlegel, 1846) species Tribolodon hakonensis (Günther, 1877) species Gnathopogon elongatus (Temminck et Schlegel, 1846) family Cobitidae species Cobitis taenia Linnaeus, 1758 species Misgurnus anguillicaudatus (Cantor, 1842) family Siluridae species Silurus asotus Linnaeus, 1758 family Gobiidae genus Rhinogobius Gill, 1859 family Cottidae species Cottus pollux Günther, 1873 family Amblycipitidae species Liobagrus reini HilGündorf, 1878 family Osmeridae species Plecoglossus altivelis (Temminck et Schlegel, 1846) Temporal coverage Data range:2024-10-22 - 2024-10-29. 6Itsukushima R et al Usage licence Usage licence:Other IP rights notes:This work is licensed under a Creative Commons Attribution (CC-BY 4.0) Licence. Data resources Data package title:Database of fish fauna collected from river channels on alluvial fans in the Kofu Basin, Japan Resource link: https://www.gbif.org/dataset/07b5664c-4dda-49e1-9f3a-c8273a7c12fb Alternative identifiers: https://doi.org/10.15468/madkz2 Number of data sets:1 Data set name:Database of fish fauna collected from river channels on alluvial fans in the Kofu Basin, Japan Download URL: https://ipt.pensoft.net/archive.do?r=database_fish_fauna_alluvial _fan_kofu_basin&v=1.2 Description: Surveys were conducted at 26 sites in the four rivers on alluvial fans flowing through the Kofu Basin in the central part of the Japanese archipelago. As a result of this investigation, 15 species and one genus (only the genus could be identified) within seven families were observed, with 2,265 individuals recorded across the 26 sites. Column label Column description occurrenceID An identifier for the Occurrence. basisOfRecord The specific nature of the data record. samplingProtocol The names of, references to, or descriptions of the methods or protocols used during an Event. eventDate The date-time or interval during which an Event occurred. scientificName The full scientific name. scientificNameAuthorship The authorship information for the scientificName formatted according to the conventions of the applicable nomenclaturalCode. kingdom The full scientific name of the kingdom in which the taxon is classified. phylum The full scientific name of the phylum or division in which the taxon is classified. class The full scientific name of the class in which the taxon is classified. Database of fish fauna collected from river channels on alluvial fans in ... 7 order The full scientific name of the order in which the taxon is classified. family The full scientific name of the family in which the taxon is classified. taxonRank The taxonomic rank of the most specific name in the scientificName as it appears in the original record. identifiedBy A list (concatenated and separated) of names of people, groups or organisations who assigned the Taxon to the subject. recordedBy A list (concatenated and separated) of the globally unique identifier for the person, people, groups or organisations responsible for recording the original Occurrence. decimalLatitude The geographic latitude (in decimal degrees, using the spatial reference system given in geodeticDatum) of the geographic centre of a Location. decimalLongitude The geographic longitude (in decimal degrees, using the spatial reference system given in geodeticDatum) of the geographic centre of a Location. coordinateUncertaintyInMetres The horizontal distance (in metres) from the given decimalLatitude and decimalLongitude describing the smallest circle containing the whole of the Location. geodeticDatum The ellipsoid, geodetic datum or spatial reference system (SRS) upon which the geographic coordinates given in decimalLatitude and decimalLongitude are based. countryCode The standard code for the country in which the Location occurs. Recommended best practice is to use ISO 3166-1-alpha-2 country codes. individualCount The number of individuals represented present at the time of the Occurrence. occurrenceStatus A statement about the presence or absence of a Taxon at a Location. catalogNumber A list (concatenated and separated) of previous or alternative fully qualified catalogue numbers or other human-used identifiers for the same Occurrence, whether in the current or any other dataset or collection. language A language of the resource. Recommended best practice is to use a controlled vocabulary, such as RFC 4646 [RFC4646]. country The name of the country or major administrative unit in which the Location occurs. Recommended best practice is to use a controlled vocabulary, such as the Getty Thesaurus of Geographic Names. stateProvince The name of the next smallest administrative region than country (state, province, canton, department, region etc.) in which the Location occurs. municipality The full, unabbreviated name of the next smallest administrative region than county (city, municipality etc.) in which the Location occurs. Do not use this term for a nearby named place that does not contain the actual location. waterBody The name of the waterbody in which the dcterms:Location occur. modified The four-digit year in which the Event occurred, according to the Common Era Calendar. 8Itsukushima R et al year The four-digit year in which the Event occurred, according to the Common Era Calendar. month The ordinal month in which the Event occurred. day The integer day of the month on which the Event occurred. establishmentMeans Statement about whether a dwc:Organism has been introduced to a given place and time through the direct or indirect activity of modern humans. dynamicProperties A list of additional measurements, facts, characteristics or assertions about the record. Meant to provide a mechanism for structured content. Additional information The species that appeared most frequently were Plecoglossus altivelis (Temminck et Schlegel, 1846), the genus Rhinogobius Gill, 1859 and the Cobitis taenia Linnaeus, 1758, which were widely observed. These species are the most commonly found in the gradient of the alluvial fan river channels studied (Itsukushima 2019) and they were also relatively abundant in locations affected by anthropogenic impacts, such as excavation activities. On the other hand, Cottus pollux was collected in the Kane and Ara Rivers; however, its presence was not observed in the Omo River. In contrast, Liobagrus reini was found in the Omo River, unlike Cottus pollux. Liobagrus reini and Cottus pollux are distantly related species, both nocturnal benthic carnivores. It is known that they often co-exist sympatrically in the mid-stream areas of temperate rivers in Japan (Miyadi et al. 1976, Natsumeda et al. 2016). However, in this study, the rivers inhabited by Cottus pollux and Liobagrus reini were clearly separated. The difference in food resources between the two species may explain this separation. Both species primarily rely on aquatic insects as their main food source; however, Cottus pollux is a benthos feeder, cruising widely and preying exclusively on chironomid and trichopteran larvae. On the other hand, Liobagrus reini is both a drift and benthos feeder, ambushing prey and selecting ephemeropteran nymphs in addition to chironomid and trichopteran larvae (Natsumeda et al. 2016). Therefore, it is likely that the benthic faunal composition, which serves as the food resource, differs between the rivers where Cottus pollux and Liobagrus reini are found. One possible factor is the difference in the geology of the watersheds in the rivers where Cottus pollux and Liobagrus reini were observed. It is known that differences in surface geology can influence the benthic faunal composition (Shearer and Young 2011, Tashiro and Tsujimoto 2015) and these geological differences may govern the benthic faunal resources, which, in turn, could affect the presence of these predatory fish species. Amongst the four rivers surveyed, the Midai River had significantly lower fish species richness and abundance compared to the other rivers, except at the most downstream site. The Midai River alluvial fan is a piedmont-type fan, primarily formed by the accumulation and transport of debris flows. In contrast, the other rivers traverse floor-type fans, which are basin-floor alluvial fans characterised by microtopographical features Database of fish fauna collected from river channels on alluvial fans in ... 9