Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, Fukuoka, Japan)

Biodiversity Data Journal 13: e155035 doi: 10.3897/BDJ.13.e155035 Data Paper Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, Fukuoka, Japan) Rei Itsukushima , Keigo Otsu , Soma Matsushima , Hironari Miyahara ‡ Kyushu University, Fukuoka, Japan § Kyushu Institute of Technology, Kitakyushu, Japan Corresponding author: Rei Itsukushima ([email protected]) Academic editor: Felipe Ottoni Received: 07 Apr 2025 | Accepted: 29 Jul 2025 | Published: 28 Nov 2025 Citation: Itsukushima R, Otsu K, Matsushima S, Miyahara H (2025) Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, Fukuoka, Japan). Biodiversity Data Journal 13: e155035. https://doi.org/10.3897/BDJ.13.e155035 Abstract Background Urbanisation has caused significant changes in material cycles, alterations in river flow rates and depths and modifications to habitats for aquatic organisms. These changes have led to disruptions in the movement and dispersal of aquatic species, as well as shifts in biodiversity. The loss of habitats due to urbanisation has resulted in a decline in species diversity across a variety of taxonomic groups. Aquatic organisms, in particular, are adversely affected by habitat loss caused by river channel modifications and the invasion of non-native species. It is generally reported that, in regions where invasive species have established and native species have declined, fish fauna tend to homogenise, leading to a substantial reduction in diversity. However, the impact of urbanisation on fish fauna varies depending on local ecosystems, the degree of urbanisation and the time elapsed since urban development. Therefore, it is crucial to gather region-specific information on how fish fauna have been altered by urbanisation. The study area in this research, the Kitakyushu metropolitan area, is one of Japan's oldest heavy industrial zones and many of its rivers have been affected by channel straightening and concrete lining. ‡,§ § § § © 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 100 locations within the Kitakyushu metropolitan area during the summer period (from 16 July to 4 October 2024), focusing on river sections modified by channel straightening and concrete lining due to urbanisation. The survey resulted in collecting 30 genera and 32 species from nine orders and 19 families, for a total of 9,253 individuals. Amongst the species collected, rare species, such as the Bitterling, Liobagrus reini and Misgurnus anguillicaudatus, were also found (The Japanese Red List). Although the number of individuals was limited, these native rare species were found in inhabited rivers significantly altered by human activity. Additionally, invasive species including Lepomis macrochirus, Micropterus salmoides (Lacepède, 1802) and Channa argus (Cantor, 1842) were recorded. Despite accounting for only 0.5% of the total fish population, the highly predatory nature of these invasive species warrants proactive management, including the enhancement of impounded water environments through structures such as weirs, to mitigate their potential ecological impact. Keywords channel degradation, fish fauna, habitat loss, invasive species, urbanisation Introduction Urban populations continue to grow and the importance of cities is increasing when considering the global environment. In recent years, the significance of ecosystem services provided by urban rivers has been recognised (Chien and Saito 2021) and the health of urban rivers is now seen as a critical element for achieving sustainable urban development (Guimarães et al. 2021). For the natural restoration of urban rivers, a systematic and quantitative understanding of the impacts of urbanisation on rivers is essential, yet scientific knowledge in this area remains insufficient. In Japan, due to the need to address increased flood flows resulting from urbanisation and the constraints of available land, most rivers in urban areas have been primarily designed for flood control, often without sufficient consideration for environmental factors. Urban waterbodies, particularly urban streams, possess the potential to offer a diverse array of ecosystem services, ranging from habitat and energy provision to pollutant removal, improved amenities and recreational opportunities. In densely developed urban areas, they can serve as critical focal points for re-establishing connections between humans and the natural environment (Lundy and Wade 2011). There is growing recognition within the country of the importance of the ecosystem services provided by urban rivers and momentum for natural restoration is steadily increasing (Itsukushima and Ohtsuki 2021). Habitat loss, pollution, contamination and the reduction of resources for basal species — thereby affecting the entire food chain — due to urbanisation has led to a decline in 2Itsukushima R et al species diversity across various taxonomic groups (Blair 1999, Mckinney 2008Kowarik 2011). Amongst these, aquatic organisms are particularly affected by the loss of habitats due to river modifications and the invasion of non-native species as urbanisation progresses (Pauchard et al. 2006, Engman and Ramírez 2012). Fish, as top consumers in river ecosystems, are amongst the most sensitive taxa to urbanisation (Kollaus et al. 2014). In general, regions where invasive species have established themselves and native species have declined show evidence of homogenisation of fish communities, leading to significant reductions in biodiversity (Marchetti et al. 2006, Olden et al. 2006). In contrast, despite 85% of the watershed being urbanised and the majority of the Tsurumi River, which flows through Tokyo and Kanagawa, being artificially modified, rare fish species have been observed in certain areas. For example, the Tanakia lanceolata (Temminck & Schlegel, 1846), which was previously believed to be extinct in the study area, has been found in the low-velocity zones near tributary confluences. Additionally, in areas where riparian forests have been minimally preserved, even in sections of the river that are lined with concrete, the presence of the endangered Lefua echigonia (Jordan and Richardson, 1907) has been confirmed (Itsukushima and Maruoka 2022, Itsukushima et al. 2024). Thus, it has been suggested that, even in urban watersheds with degraded environmental conditions, substantial improvements in biodiversity can be achieved through natural restoration. Furthermore, although urban rivers often suffer from environmental degradation and insufficient data on their biota, the importance of conducting thorough surveys of the biological communities in urban areas for effective environmental restoration has been emphasised. Although interest in the biodiversity of urban rivers is increasing, there is still a lack of sufficient data and current knowledge remains inadequate to effectively support the restoration and conservation of urban river environments. The target area of this study, the Kitakyushu metropolitan area, is one of Japan's oldest industrial zones, where heavy chemical industries, particularly the steel industry, have been prominent since the early 20 century. As a result of urbanisation, many of the region's rivers have been transformed into concrete-lined channels, leading to the anticipated degradation of river ecosystems (Suppl. material 1). However, due to the large number of small and mediumsized rivers, monitoring by government agencies and local authorities has been limited and there is a lack of comprehensive information on the regional biota. This paper reports the findings of a survey on the fish fauna of the Kitakyushu metropolitan area, where such data are scarce. The study aims to provide critical foundational knowledge for the environmental conservation and natural restoration of small and medium-sized urban rivers, contributing to a better understanding and management of these ecosystems in the face of urban pressures. Sampling methods Description:This study was conducted at 100 sites across 14 river basins flowing through the Kitakyushu metropolitan area in Japan (Fig. 1). The selected rivers ranged in watershed area from 2.1 km² (Muranaka River) to 113 km² (Murasakigawa River), th Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, ... 3 representing small and medium-sized rivers. Kitakyushu City, the core of the Kitakyushu Industrial Zone, is one of Japan’s major industrial regions and a hub for heavy and chemical industries, particularly iron and steel production. With industrialisation, the population became concentrated and although it has declined in recent years, the City had a population of 939,000 in 2020. Many of the small and medium-sized rivers in the area have been canalised with concrete, leading to the degradation of river ecosystems in numerous locations. However, there is a lack of comprehensive biological data for the broader region of Kitakyushu. Thus, fish surveys were conducted at 100 sites, primarily focusing on smaller rivers where data are scarce. In this study, a total of 9,253 individuals were recorded, with species identified both on-site and in the laboratory according to the identification keys of Kawanabe and Mizuno (1989) and Seno (2007). The fish surveys were carried out during the summer period (from 16 July to 4 October 2024). The average daily temperature on the survey days was 26.5°C, according to data from the Japan Meteorological Agency's Yahata observatory. Sampling description:The fish survey was conducted using a pulsed DC Smith-Root Model 12-A p DC backpack electrofisher (Smith-Root Inc., Vancouver, WA, U.S.A.) at each habitat type (rapid, run, pool, glide, slack and backwater) across 100 survey stations. The length of each survey section was one river reach, approximately 10 times the width of the river channel. The electrofisher was set to an output voltage of 120 V and operated in the standard pulse mode, which delivers continuous pulsed waveforms at regular intervals (frequency: 60 Hz). The duration of use ranged from 30 to 90 minutes, depending on the size of the river channel and the number of habitats. We employed a backpack electrofisher due to its high capture efficiency through visual detection and netting, as it temporarily immobilises fish and induces surfacing. Moreover, since the fish recover within a short period and can be released back into the habitat, this method Figure 1. Location of the study sites. The study focused on 100 locations across 14 river systems.  4Itsukushima R et al allows for the assessment of population size and diversity, while minimising stress on the fish. The scientific names of the taxa, their authorship and year of publication and original descriptions followed Fricke et al. (2025a) and Fricke et al. (2025b). In addition, to compare species diversity and the number of individuals between sites with and without the presence of non-native species, the Wilcoxon rank-sum test was conducted using the statistical software R (version 4.5.1). The significance level was set at 5% (p < 0.05). Geographic coverage Description:Surveys were conducted at 100 sites in the 14 river systems located in the Kitakyushu metropolitan area during summer, focusing on river channels that have been straightened or converted to concrete channels due to urbanisation. Coordinates:33.78448 and 33.92905 Latitude; 130.73471 and 130.99965 Longitude. Taxonomic coverage Description: Characteristics of the fish survey results As a result of the surveys, nine orders, 19 families, 30 genera and 32 species were identified, with 9,253 individuals being collected from the 100 stations. The highest species richness was recorded at sites belonging to the Murasaki River and Shii River, with 14 species collected. The greatest number of individuals was recorded at a site belonging to the Itabitsu River, with 548 individuals being collected. By contrast, fish were not confirmed in the site belonging to the Okuhata R. The highest number of individuals found was 3,146 of Nipponocypris temminckii (Temminck et Schlegel, 1846), which appeared in 76 stations (Table 1). Rank Scientific Name Number of occurrences Order Cypriniformes family Cyprinidae species Cyprinus carpio Linnaeus, 1758 41 species Carassius langsdorfii Temminck & Schlegel, 1846 282 family Acheilognathidae species Acheilognathus rhombeus (Temminck & Schlegel, 1846) 1 species Tanakia lanceolata (Temminck & Schlegel, 1846)* 9 Table 1. The occurrence of fish taxa in the Kitakyushu metropolitan area, Fukuoka, Japan. Rare species are indicated with * and invasive species with ** in the table. Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, ... 5 Rank Scientific Name Number of occurrences species Tanakia limbata (Temminck & Schlegel, 1846)* 56 family Gobionidae species Squalidus gracilis (Temminck & Schlegel 1846) 135 species Gnathopogon elongatus (Temminck & Schlegel, 1846) 20 species Pseudogobio esocinus (Temminck & Schlegel, 1846) 61 species Pungtungia herzi Herzenstein, 1892 587 family Xenocyprididae species Nipponocypris temminckii (Temminck et Schlegel, 1846) 3146 species Zacco platypus (Temminck et Schlegel, 1846) 1697 family Leuciscidae species Rhynchocypris jouyi (Jordan & Snyder, 1901) 60 family Cobitidae species Cobitis sp. 3 species Cobitis matsubarae Okada & Ikeda, 1939* 22 species Misgurnus anguillicaudatus (Cantor, 1842)* 55 Order Gobiiformes family Oxudercidae species Rhinogobius nagoyae Jordan & Seale, 1906 858 species Rhinogobius sp. 973 species Acanthogobius flavimanus (Temminck & Schlegel, 1845) 11 species Rhinogobius similis Gill 1859 163 species Tridentiger brevispinis Katsuyama, Arai & Nakamura, 1972 100 species Gymnogobius urotaenia (Hilgendorf, 1879) 20 Order Centrarchiformes family Centrarchidae species Lepomis macrochirus Rafinesque, 1819** 19 species Micropterus salmoides (Lacepède 1802)** 24 Order Osmeriformes family Plecoglossidae species Plecoglossus altivelis (Temminck & Schlegel 1846) 35 6Itsukushima R et al Rank Scientific Name Number of occurrences Order Perciformes family Odontobutidae species Odontobutis obscura (Temminck & Schlegel, 1845) 703 family Lateolabracidae species Lateolabrax japonicus (Cuvier, 1828) 1 family Channidae species Channa argus (Cantor, 1842)** 3 family Sinipercidae species Coreoperca kawamebari (Temminck & Schlegel, 1843)* 48 Order Mugiliformes family Mugilidae species Mugil cephalus Linnaeus, 1758 3 Order Siluriformes family Bagridae species Tachysurus nudiceps (Sauvage, 1883) 9 family Amblycipitidae species Liobagrus reini Hilgendorf, 1878* 1 family Siluridae species Silurus asotus Linnaeus, 1758 4 Order Beloniformes family Adrianichthyidae species Oryzias latipes (Temminck & Schlegel, 1846)* 46 Order Anguilliformes family Anguillidae species Anguilla japonica Temminck & Schlegel, 1846* 57 Taxonomic coverage The orders were Cypriniformes (15 species), Gobiiformes (6 speices), Perciformes (4 species), Siluriformes (3 species), Centrarchiformes (2 species), Anguilliformes (1 species), Beloniformes (1 species), Mugiliformes (1 species) and Osmeriformes (1 species) (Fig. 2). The families were Oxudercidae (6 species), Gobionidae (4 species), Acheilognathidae (3 species), Cobitidae (3 species), Centrarchidae (2 species), Cyprinidae (2 species), Xenocyprididae (2 species), Adrianichthyidae (1 species), Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, ... 7 Amblycipitidae (1 species), Anguillidae (1 species), Bagridae (1 species), Channidae (1 species), Lateolabracidae (1 species), Leuciscidae (1 species), Mugilidae (1 species), Odontobutidae (1 species), Plecoglossidae (1 species), Siluridae (1 species) and Sinipercidae (1 species) (Fig. 3). According to the Red Data Book published by the Fukuoka Prefecture in 2014, Anguilla japonica Temminck & Schlegel 1846 was determined as EN (Endangered). Tanakia Figure 2. Taxonomic coverage (by order).  Figure 3. Taxonomic coverage (by family).  8Itsukushima R et al lanceolata (Temminck & Schlegel, 1846), Misgurnus anguillicaudatus (Cantor, 1842) and Liobagrus reinii Hilgendorf 1878 were determined as VU (Vulnerable). Plecoglossus altivelis (Temminck & Schlegel, 1846), Acheilognathus rhombeus (Temminck & Schlegel, 1846), Oryzias latipes (Temminck & Schlegel, 1846), Cobitis matsubarae Okada & Ikeda 1939 and Tanakia limbata (Temminck & Schlegel, 1846) were determined as NT (Near Threatened). In the Ministry of the Environment's Red Data Book (2020) for Japan, Plecoglossus altivelis and Acheilognathus rhombeus are not listed amongst the species mentioned above. On the other hand, Coreoperca kawamebari (Temminck & Schlegel, 1843) is listed as EN (Endangered). 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:A database of fish fauna in Kitakyushu metropolitan area Resource link: https://doi.org/10.15468/tb9cvk Alternative identifiers: https://ipt.pensoft.net/resource?r=database_fish_fauna_ kitakyushu Number of data sets:1 Data set name:A database of fish fauna in Kitakyushu metropolitan area Download URL: https://ipt.pensoft.net/archive.do?r=database_fish_fauna_ kitakyushu&v=1.8 Description: Surveys were conducted at 100 sites in the 14 river systems located in the Kitakyushu metropolitan area, focusing on river channels that have been straightened or converted to concrete channels due to urbanisation. As a result of this investigation, 30 genera, 32 species and 9,253 individuals were collected ( Itsukushima 2025). 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. Ichthyofauna in a highly urbanised area (Kitakyushu metropolitan area, ... 9 Supplementary material Suppl. material 1: Landscape photograph of the surveyed site Authors: Itsukushima R Data type: images Brief description: Landscape photograph of the surveyed site with a concrete-lined channel. Download file (975.86 kb) 16 Itsukushima R et al