Fish Fauna and Features of the Nakagawa River (Japan: Kanto Region)

River Fish

In this article, I will introduce Japanese rivers through the latest list of fish species and geographical characteristics, focusing on the Nakagawa River in the Kanto region.

If you are a traveler to Japan with an interest in rivers and fish, I recommend visiting the Nakagawa River in the Kanto region. The Nakagawa stretches for 150 kilometers, originating in Tochigi Prefecture and flowing into the Pacific Ocean in Ibaraki Prefecture. It is the 19th longest river in Japan and the third longest in the Kanto region. With a source elevation of 1,750 meters, it features rapid streams, unlike many continental rivers. Accessible by train and bus from Tokyo, this river offers a premier experience of the relationship between people and river fish. In the Nakagawa, you can encounter natural sweetfish (ayu) and salmon. It also presents an interesting mix of fish species, blending northern and southern varieties. Let’s delve into the Nakagawa River in this edition.

→ Please refer to this site for information about fish throughout Japan.

1.Fish Fauna

According to a national environmental survey on Japanese rivers, the Nakagawa River was home to 72 fish species in 2016 and 91 species in 2021. A distinctive feature of the Nakagawa is the coexistence of species like those of the Salmonidae family, which are primarily found in northern areas, with species like those of the Cyprinidae and Gobiidae families, more common in southern regions. Particularly noteworthy is one of its tributaries, Lake Hinuma, known as the southern limit for herring.

Due to Japan’s elongated shape stretching from north to south, the Nakagawa lies at the boundary between northern and southern fish species, being at the very center of this boundary. In recent years, there has been a noticeable shift in this boundary, with a decline in northern species like salmon, possibly due to global warming. Simultaneously, there’s an influx of southern and non-native species, which is likely due to human activities, as fish cannot naturally traverse long distances over land. Therefore, it seems the distribution boundary is shifting due to two factors: global warming and human-mediated biotic movement.

Thus, the Nakagawa River may be seen as a litmus test, sensitively reflecting changes in the composition of fish species. While there is a hope for stability, the reality appears to be less straightforward. The future trends of this river will undoubtedly continue to be of interest.

Plecoglossus altivelis altivelis (Ayu)
Oncorhynchus keta (Syake)

The List of Freshwater Fish Species in the Nakagawa River

No.FamilyEnglish NameSpeciesLife CycleOrigin Status20162021
1PetromyzontidaeLampreysLethenteron sp.N and/or sp.SFrNative
2DasyatidaeStingraysHemitrygon akajeiENative 
3ElopidaeTenpoundersElops hawaiensisENative 
4AnguillidaeEelsAnguilla japonicaMNative
5ClupeidaeHerringsSardinella zunasiENative
6  Konosirus punctatusENative
7CyprinidaeCarps and MinnowsCyprinus carpioFrIntorduced
8  Carassius cuvieriFrNon-indigenous
9  Carassius sp.FrNative
10  Tanakia lanceolataFrNative 
11  Tanakia limbataFrNon-indigenous 
12  Acheilognathus melanogasterFrNative
13  Acheilognathus tabira erythropterusFrNative 
14  Rhodeus ocellatus ocellatusFrIntorduced
15  Opsariichthys platypusFrNative
16  Candidia temminckiiFrNon-indigenous
17  Candidia sieboldiiFrNon-indigenous
18  Rhynchocypris lagowskii steindachneriFrNative 
19  Pseudaspius brandtii marutaMNative
20  Pseudaspius hakonensisFrNative
21  Pseudorasbora parvaFrNative
22  Gnathopogon elongatus elongatusFrNon-indigenous
23  Pseudogobio esocinusFrNative
24  Abbottina rivularisFrNon-indigenous
25  Hemibarbus barbusFrNative
26  Squalidus chankaensis biwaeFrNon-indigenous
27CobitidaeLoachesMisgurnus anguillicaudatusFrNative
28  Misgurnus dabryanusFrIntorduced
29  Cobitis sp. BIWAE type CFrNative
30NemacheilidaeStone LoachesLefua echigoniaFrNative
31BagridaeBagrid CatfishesTachysurus tokiensisFrNative
32SiluridaeSheatfishesSilurus asotusFrNative
33PlotosidaeEeltail catfishPlotosus japonicusENative 
34OsmeridaeSmeltsHypomesus nipponensisMNative
35PlecoglossidaeAyu or SweetfishPlecoglossus altivelis altivelisMNative
36SalangidaeIcefishes or SweetfishSalangichthys microdonMNative
37  Salangichthys ishikawaeMNative 
38SalmonidaeSalmon and TroutSalvelinus leucomaenisFrNative
39  Oncorhynchus ketaMNative 
40  Oncorhynchus masou masouMNative
41MugilidaeMulletsMugil cephalus cephalusENative
42  Planiliza lauvergniiENative 
43PoeciliidaeLivebearersGambusia affinisFrIntorduced 
44AdrianichthyidaeRicefishesOryzias latipesFrNative
45HemiramphidaeHalfbeaksHyporhamphus intermediusENative 
46  Hyporhamphus sajoriENative 
47PlatycephalidaeFlatheadsPlatycephalus sp.2ENative
48LateolabracidaeAsian SeabassesLateolabrax japonicusENative
49CentrarchidaeSunfishesLepomis macrochirus macrochirusFrIntorduced
50  Micropterus salmoidesFrIntorduced
51  Micropterus dolomieu dolomieuFrIntorduced
52CarangidaeJacks and PomanosScomberoides lysanENative 
53  Caranx sexfasciatusENative
54  Caranx ignobilisENative 
55LeiognathidaePonyfishesNuchequula nuchalisENative 
56GerreidaeMojarrasGerres equulusENative 
57HaemulidaeGruntsPlectorhinchus cinctusENative 
58SparidaePorgiesRhabdosargus sarbaENative 
59  Acanthopagrus schlegeliiENative
60  Acanthopagrus latusENative 
61SillaginidaeSillagos or WhitingSillago japonicaENative 
62EmbiotocidaeSurfperchesDitrema temminckii temminckiiENative 
63TeraponidaeTeraponidsTerapon jarbuaENative
64  Rhynchopelates oxyrhynchusENative
65KuhliidaeAholeholesKuhlia marginataENative 
66CottidaeSculpinsCottus polluxFrNative
67  Cottus reiniiMNative
68  Ocynectes maschalisENative 
69  Pseudoblennius cottoidesENative 
70PholidaeGunnelsPholis nebulosaENative 
71EleotridaeSleepersEleotris oxycephalaFrNative
72GobiidaeGobiesLuciogobius guttatusENative
73  Eutaeniichthys gilliENative 
74  Leucopsarion petersiiFrNative 
75  Acanthogobius flavimanusENative
76  Acanthogobius lactipesENative
77  Sicyopterus japonicusMNative
78  Mugilogobius abeiENative
79  Pseudogobius masagoENative 
80  Tridentiger trigonocephalusENative 
81  Tridentiger bifasciatusENative
82  Tridentiger brevispinisFrNative
83  Redigobius bikolanusENative 
84  Rhinogobius nagoyaeMNative
85  Rhinogobius fluviatilisMNative
86  Rhinogobius similisMNative 
87  Rhinogobius sp.OR unidentifiedMNative
88  Glossogobius olivaceusENative 
89  Favonigobius gymnauchenENative
90  Gymnogobius petschiliensisMNative
91  Gymnogobius urotaeniaMNative
92  Gymnogobius heptacanthusENative 
93  Gymnogobius macrognathosENative 
94  Chaenogobius annularisENative 
95  Chaenogobius gulosusENative 
96ChannidaeSnakeheadsChanna argusFrIntorduced 
97ParalichthyidaeLarge tooth FloundersParalichthys olivaceusENative
98PleuronectidaeRighteye FlounderPlatichthys stellatusENative 
99  Platichthys bicoloratusENative
100CynoglossidaeTonguefishesParaplagusia japonicaENative 
101TetraodontidaePufferfishTakifugu flavipterusENative 
102  Takifugu alboplumbeusENative
 Total40 families102 Species  7291
* : This data is based on the national census of the river environment in Japan ( , which is conducted every five years.
** : While some species have been subdivided, the names of species have been retained as they were previously for comparison with past data.
*** : Salvelinus leucomaenis and Oncorhynchus masou masou are included in the record because the author has confirmed their perennial habitat in the upper reaches of the survey area.
****: Classification of Life Cycles
・ Freshwater: Species that can spend their entire life in freshwater.
・ Migratory: Species that must migrate between freshwater and saltwater during their lifetime.
・ Euryhaline: Species that primarily inhabit brackish or saltwater, but may also venture into freshwater.
However, since there are species with intermediate characteristics, such species have been categorized at the author’s discretion.
2. Features as a RIver

The Nakagawa River is a clear stream blessed with the natural beauty of the Kanto region. Its upper reaches lie within the Nikko National Park, while the middle course is protected as the Nakagawa Prefectural Nature Park. Despite flowing through the heavily urbanized Kanto region, this area maintains its natural environment, supporting a rich ecosystem.

The river basin is abundant with fish species such as sweetfish (ayu) and salmon, and their upstream migration is well-known. Particularly, the local fishing of ayu and salmon is a highlight, with grilled ayu being a popular gourmet attraction for tourists along the middle course of the river from Tochigi to Ibaraki Prefecture in early summer. Moreover, visitors can experience ayu fishing and observe various other fish species in activities like ‘nagashi’ (as introduced in this video).

In Sarado, Otawara City, Tochigi Prefecture, there is a prefectural fisheries experimental station dedicated to freshwater fish research. Adjacent to this facility is the Nakagawa Aquatic Park, one of the leading freshwater aquariums in the country, where you can learn about the freshwater fish of the Nakagawa River. Visiting this region offers an in-depth understanding of the rich nature and ecosystem of the Nakagawa River.

3. Conclusion

The main points of the Naka River summarized in this article are as follows.
It is a really nice river and you should come and enjoy it. I will definitely be there at least once this year.

a. It reflects the diverse aquatic biodiversity of the region, with a unique mix of fish species from northern and southern Japan.
b. Despite its proximity to urban areas, the river ecosystem is well preserved, with some parts protected by national and prefectural parks. They also have a close relationship with people. In particular, the traditional fishing method, ayu fishing by Yana, is worth seeing.
c. The river is a likely environmental indicator of changes in fish populations due to global warming and anthropogenic influences.

See you soon.