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🛏 | Sky panorama open-air secret hot spring "Fujishichi Onsen Saiunso" at an altitude of 1,400 meters [Column: Onsen!on…


Sky panorama open-air secret hot spring "Fujishichi Onsen Saiunso" at an altitude of 1,400 meters [Column: Onsen!on…

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You can find dishes made with local Hachimantai ingredients such as fresh wild plants and river fish.

(Toshichi Onsen, Hachimantai City, Iwate Prefecture) In May, the number of summer-like days has increased beyond spring.It's hot rather than warm ... → Continue reading


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Freshwater fish

Freshwater fish(Tansuigyo,(British: Freshwater fish) IsfreshwaterCan live inFishesGeneric name for.Freshwater fish2006At that time, about 1 species were known, accounting for about 2,000% of the 2 species of modern fish.[1]..The fish that mainly live in riversRiver fishOften referred to as ("Kawazakana" or "Kawauo").

Inhabited by freshwater fishRiver,LakeSuch asLand waterLess than 0.01% of all water on earth, with an average volume per speciesSaltwater fishOnly about 7,500 / 1 of[3]..Much narrower than saltwater fishBiosphereRemarkable freshwater fish acquired inbiodiversityIn freshwater areas where the average depth is shallowPrimary productionIs very high, quarantine is easily generatedSpeciationIntricately intertwined, such as being easily promotedEcologyTargetGeologyIt is believed that it was brought about by a certain factor.[3].

Classification of freshwater fish

Advance into freshwater areasAdaptationSaltwater fish turned into freshwater fish進化It is speculated that it was done.The key to adaptation wasDocosahexaenoic acidFads2 that synthesizes (DHA)geneStudies have shown that[4].

In modern times, there are various forms of fish entering and exiting at the boundary between freshwater and seawater, making it difficult to clearly define "freshwater fish".[5]..The classification of freshwater fish is the degree of resistance to seawater, orLife historyOften done based on the proportion of freshwater in the area[5].

As an example of classification based on life historyKoi,catfishThose who live their lives in fresh waterPure freshwater fish(Primary freshwater fish[6]),eel,SweetfishWhat to spend a lifetime in seawater likeMigratory fish,ボ ラ,Japanese sea bassEtc. originallySaltwater fish-Brackish fishWhat is invading freshwaterPeripheral freshwater fish[7]Classify as[5].

However, there are many differences between researchers in the classification method.Medaka-KadashiThose that can accidentally enter the sea area while living in fresh water, such asSecondary freshwater fishHowever, there are cases where this is included in pure freshwater fish in a broad sense, and there are cases where it is treated as an independent division.[5]. Also,SalmonSuch asMigratory fishIs often included in marginal freshwater fish[3].


Pure freshwater fish cannot pass through seawater, so they were connected in freshwater.Water systemIt is difficult to get out of the area, and its distribution range is strongly influenced by geography.[5]..Except for manual importsRiver captureUnless there is such a thing, it rarely moves to other rivers, and there are many unique speciations by region.Biwa lake,Lake BaikalEtc., so-calledAncient lakeIt has a long history of being a freshwater area, and many in its large-scale areas.Endemic speciesCan be seen.Amazon riverThe number of fish species is大西洋It is said that there are more than the whole.

Of freshwater fishDisjunct distributionMany are strongly associated with geographic changes.LungfishThe distribution of classes is one example, with independent genera.Southern hemisphere OfAfrican continent,Australian continent,South AmericaThere is one genus in each.This is this continentGondwana ContinentIt is believed that it originated from the fact that it was a land continuation.

Distribution based on biogeographic realms

Like other biota,Biogeographic areaClassification based on is useful for understanding the distribution of freshwater fish[8]..Below,Wallace 1876Outline the distribution of freshwater fish in the six geographic regions proposed in.In this section, freshwater fish are broadly divided into three species: pure freshwater fish (primary freshwater fish), secondary freshwater fish, and peripheral freshwater fish.

Xinbei District

Xinbei District TheMexican PlateauNorth ofNorth AmericaIs an area containing[8]..At least 14 families of pure freshwater fish are known, overallCarp family,Suckers,,,Sunfish familyAbout 950 species are distributed[8]..Over 350 species of freshwater fish live in the water system derived fromTemperateIt is the most diverse area in the region.[8].

Neotropical realm

Neotropical realmToSouth AmericaCentral americaIs included and is the area with the most abundant freshwater fish fauna in the world.[9]..There are 32 families of pure freshwater fish alone, 4,475 species are known in total, and it is estimated that there are more than 1,500 undescribed species.[9].CatfishWith 13 departmentsCharaciformesThere are more than 8 species in each of the eight families, andGymnotiformes5 departmentsCichlid family(Perch) Etc. are the groups that characterize this area[9]..On the other hand, the Cyprinidae and Suckers, which were dominant in North America, are not found in South America at all.[9].

It is also characterized by the fact that some of the groups that were originally saltwater fish have been adapted as pure freshwater fish (so-called).Freshwater ray),Batrachoididae,Needlefish family,DrumaceaeSome of them are known[9].

Old Kita Ward

Old Kita Ward TheEuropeからEast AsiaAlthough it is a vast area leading up to, the number of pure freshwater fish distributed is limited to 14 families.[10]..CyprinidaeLoach familyThere are many catfish, and only about 4 species of 10 families are counted.[10]..aside from that·Pike familyEtc., and at least 500 species are known in total[10].

African area

African Area (Afrotropical realm) Is distributed with a variety of freshwater fish, and a total of 27 species from 47 families, including 2,000 families of pure freshwater fish, inhabit.[10]..Cypriniformes, catfish, characiformes, etc.OstariophysiCompanions occupy half of them[10].

Toyo Ward

Toyo WardIs mainlyIndian subcontinentSoutheast AsiaWallace consists of a border with the Australasian RealmBorneoBaliPulling to the east of (Wallace line[11]..28 families of pure freshwater fish are distributed, 12 of which belong to the order Catfish.[11]..4 families of Cypriniformes are known, and 3 families other than Cyprinidae (Loach family・ ・Hillstream loach) Is a group that shows diversity, especially in this area.[11]..Except for osteophysiSnakehead family,Mastacembelidae,Anabas testudineusIs characteristic of[11].

Australasian realm

Australasian realmToAustralian continentWhen,New GuineaIncludes island areas east of the Wallace Line[12]..Only two species of pure freshwater fish are known in the area, both of whichAncient fishIs[12]..There are two other secondary freshwater fish, and peripheral freshwater fish.Melanotaenia・ 16 families are distributed[12].

Human influence

In many modern areas, the range and abundance of freshwater fish is exposed to human disturbance.in JapanSweetfish,Rainbow troutOf useful fish species such asReleaseAlong with this, there are cases where other fish mixed in it are also expanding their distribution, and the disturbance of the distribution of wild freshwater fish has become a problem.For example, by capturing Koayu from Lake Biwa and releasing it into other rivers,Oikawa,Kawamutu,Pungtungia herzi,Fluffy,Lotus,Wataka,FurthermoreBluegill,black bus,Rigyo,SougyoSuch asExotic speciesIs also mixed with sweetfish and is expanding its distribution.

Similar cases are known all over the world.In particular, transplantation of useful fish species such as trout has been carried out all over the world since the end of the 19th century, and there are known cases where endemic species of origin have become extinct or endangered.Lake TiticacaOne of the endemic species,Titicaca orestiasIs an example.MosquitofishMosquitoesIt was introduced into the tropical regions of the world for the control of species.


[How to use footnotes]
  1. ^ "Fishes of the World Fourth Edition" pp.11-14
  2. ^ "Japanese Freshwater Fish Revised Edition" pp.426-429
  3. ^ a b c "The Diversity of Fishes Second Edition" p.339
  4. ^ "From the sea to rivers and lakes! Discovery of the key gene that supported the advancement of fish into freshwater-If you synthesize DHA yourself, you can live even if you are away from the sea"National Institute of GeneticsPress release and “A key metabolic gene for recurrent freshwater colonization and radiation in fishes”"Science』May 2019, 5 issue. Retrieved June 31, 2019.
  5. ^ a b c d e "Introduction to Fish Studies" pp.53-54
  6. ^ British: primary
  7. ^ British: peripheral
  8. ^ a b c d "The Diversity of Fishes Second Edition" pp.339-345
  9. ^ a b c d e "The Diversity of Fishes Second Edition" pp.345-346
  10. ^ a b c d e "The Diversity of Fishes Second Edition" p.346
  11. ^ a b c d "The Diversity of Fishes Second Edition" pp.346-347
  12. ^ a b c "The Diversity of Fishes Second Edition" p.347


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