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Freshwater fish

Freshwater fish refers to fish that can live in waters with a salinity of less than 0.05%, or fish that must spend their entire lives in freshwater. There are nearly 3,000 species of fish in my country, of which more than 1,000 are freshwater fish. The more common freshwater fish species include Cypriniformes, Siluriformes, Characidae, Syngnathidae, Amphioxus, etc. Since freshwater environments are smaller in area than oceans but more diverse (rivers, lakes, wetlands, streams, mountain streams, groundwater systems, etc.), freshwater fish present rich morphological and biological diversity under the influence of geographical isolation, climate and hydrological conditions. The following will help your website users understand the evolutionary context and diverse distribution of freshwater fish, and also show their important position in ecology and human society.

I. Introduction to Freshwater Fishes

1. Definition and Key Characteristics

  • Habitat: Freshwater fishes primarily live in low-salinity waters (usually under 0.5‰), including rivers, lakes, swamps, streams, and other inland waters. Some species may frequent estuaries or slightly brackish water.

  • Osmoregulation: To prevent excessive water intake and electrolyte loss, freshwater fishes excrete large amounts of diluted urine and actively retain salts through their kidneys and gills.

  • Diversity: Despite covering a relatively small portion of Earth’s surface, freshwater ecosystems host a remarkable variety of fish species—often due to geographical barriers (waterfalls, river systems) and past climatic/tectonic events. Large lakes in Africa, the Amazon Basin, and Southeast Asian river networks are famous for their high fish diversity and endemism.

2. Major Groups

  • Cartilaginous Fishes (Class Chondrichthyes): Rare in fresh water; only a few examples (such as certain sawfishes or bull sharks) can enter or remain in freshwater habitats.

  • Bony Fishes (Class Osteichthyes): Specifically, the Actinopterygii (ray-finned fishes) dominate most freshwater environments (e.g., Cypriniformes, Siluriformes, Perciformes, Salmoniformes, Osteoglossiformes, etc.).

3. Ecological Value and Human Use

  • Aquatic Ecosystem Balance: Freshwater fishes occupy vital trophic roles, from benthic scavengers to top predators, contributing to nutrient cycling and ecosystem stability.

  • Fisheries and Aquaculture: Freshwater aquaculture (e.g., carp, tilapia, catfish) provides protein and economic benefits worldwide, while wild-capture fisheries also sustain local communities.

  • Ornamental and Cultural Significance: Ornamental fish trade (e.g., koi, goldfish, tropical aquarium species) and recreational fishing (angling) are culturally and economically important in many regions.


II. History and Evolution of Freshwater Fishes

  1. Origins and Early Evolution

  • The earliest jawed vertebrates date back to the Devonian period (around 400 million years ago). Even in these ancient times, freshwater habitats supported primitive fishes.

  • Over subsequent eras (Carboniferous, Permian, Mesozoic), bony fishes (including lungfish, lobe-finned fishes, and later the widespread ray-finned fishes) underwent significant diversification and adaptation to inland waters.

  1. Repeated Geographic Isolation and Adaptive Radiation

  • Continental drift, glaciations, and river system shifts led to the isolation of fish populations, encouraging independent evolutionary paths and high endemism.

  • Examples include African lungfish, South American electric eels, and Southeast Asian fighting fishes (Betta spp.), each illustrating unique adaptations to freshwater environments.

  1. Modern Freshwater Biodiversity

  • Today, freshwater fishes exceed 10,000 known species (about 40–45% of all fish species), yet inhabit less than 1% of Earth’s surface water.

  • Human activities (e.g., dam building, water diversion, pollution, introduction of alien species) now strongly influence many freshwater fish communities, prompting the need for conservation measures.


III. Major Orders and Families of Freshwater Fishes

Below is a classification focusing on bony fishes (Actinopterygii), which comprise the majority of freshwater species. Also included are rare instances of cartilaginous fishes that enter or live in fresh water.

A. Cartilaginous Fishes in Fresh Water (Rare Cases)

OrderFamilyRepresentative GenusExample SpeciesDistribution & Notes
Pristiformes (Sawfishes)Pristidae (Sawfishes)PristisSmalltooth Sawfish (Pristis pectinata), etc.Mostly coastal or estuarine; some individuals migrate into rivers. Overfished, now rare.
Carcharhiniformes (Ground Sharks)Carcharhinidae (Requiem Sharks)Carcharhinus leucas (Bull Shark)Bull Shark (Carcharhinus leucas)Can travel far upriver (e.g., Zambezi), exhibits high tolerance for low salinity waters.

B. Ray-Finned Fishes (Actinopterygii)

1. Order Cypriniformes (Carps, Minnows, Loaches)

FamilyRepresentative GenusExample SpeciesDistribution & Notes
Cyprinidae (Carps & Minnows)Cyprinus (Carp), Carassius (Crucian Carp), Hypophthalmichthys (Silver/Bighead Carp), Ctenopharyngodon (Grass Carp)Common Carp (Cyprinus carpio), Goldfish (Carassius auratus), Silver Carp (Hypophthalmichthys molitrix), Grass Carp (Ctenopharyngodon idella)One of the world’s largest freshwater fish families, with major economic and ornamental importance (e.g., koi, goldfish).
(Loach families such as Nemacheilidae, etc.)Triplophysa (Stone Loach, e.g., high-altitude loaches)Tibetan Stone Loach (Triplophysa gigantea), etc.Often inhabiting upland or plateau streams; many species adapted to cold, fast-flowing waters.

2. Order Siluriformes (Catfishes)

FamilyRepresentative GenusExample SpeciesDistribution & Notes
Siluridae (Sheatfishes)Silurus (Sheatfish)Amur Catfish (Silurus asotus), Wels Catfish, etc.Common in Eurasian fresh waters, often large-bodied, demersal predators/scavengers.
Clariidae (Airbreathing Catfishes)Clarias (Walking Catfish)African Sharptooth Catfish (Clarias gariepinus), etc.Native to Africa/Asia; possess accessory breathing organs, surviving in low-oxygen conditions.
Ictaluridae (North American Catfishes)IctalurusChannel Catfish (Ictalurus punctatus), etc.Important for aquaculture and recreational fishing in North America.
Callichthyidae (Armored Catfishes)Corydoras (Cory Catfish)Corydoras species (popular in aquariums)South American ornamental fish, equipped with bony plates; popular in hobby aquariums.

3. Traditional Order Perciformes (now extensively revised)

FamilyRepresentative GenusExample SpeciesDistribution & Notes
Percidae (Perches)Perca (Perch), Sander (Pike-perch), etc.European Perch (Perca fluviatilis), Walleye (Sander vitreus), etc.Found in cool/temperate Northern Hemisphere waters; prized food and sport fish.
Cichlidae (Cichlids)Oreochromis (Tilapias), Cichla (Peacock Bass), Hemichromis, etc.Nile Tilapia (Oreochromis niloticus), Peacock Bass (Cichla ocellaris), etc.Highly adaptive in Africa and South/Central America; some species (e.g., tilapia) are significant in aquaculture or invasive.
Anabantidae/Osphronemidae (Labyrinth Fishes)Betta (Fighting Fish), Trichopodus (Gouramis), etc.Siamese Fighting Fish (Betta splendens), Three-spot Gourami (Trichopodus trichopterus)Possess auxiliary breathing organ (labyrinth), can survive in oxygen-poor waters; many are ornamental fish.

4. Order Salmoniformes (Salmon, Trout, etc.)

FamilyRepresentative GenusExample SpeciesDistribution & Notes
SalmonidaeOncorhynchus, Salmo, HuchoChinook Salmon (Oncorhynchus tshawytscha), Atlantic Salmon (Salmo salar), Taimen (Hucho hucho), etc.Many are diadromous (breeding in fresh water but maturing in the sea); some remain fully freshwater. High commercial and recreational value.

5. Order Osteoglossiformes (Bonytongues)

FamilyRepresentative GenusExample SpeciesDistribution & Notes
Osteoglossidae (Bonytongues)Scleropages (Asian Arowana), Osteoglossum (Arowana)Silver Arowana (Osteoglossum bicirrhosum), Asian Arowana (Scleropages formosus)Found in South America and Southeast Asia; large ornamental fish prized for coloration and cultural value.

(Additional examples include characins, loaches, knifefishes, etc., found in global fresh waters.)


IV. Conclusion

  1. Multiple Evolutionary Lineages and Broad Diversity

    • Freshwater fishes do not descend from a single clade; they include a few cartilaginous species that tolerate fresh water and a vast array of bony fish orders. Geographical isolation and varied inland water systems have driven high speciation rates and local endemism.

  2. Ecological Functions and Economic Value

    • Freshwater fishes are key components of inland aquatic ecosystems (e.g., controlling algae, recycling nutrients, preying on insects).

    • They also support major industries: aquaculture, wild-capture fisheries, ornamental fish trade, sport fishing, and cultural traditions (e.g., koi, fighting fish).

  3. Conservation and Future Challenges

    • Habitat degradation, pollution, overfishing, and invasive species threaten many freshwater fish populations.

    • Protected river basins, habitat restoration, and breeding-and-release programs for endangered species are crucial for preserving freshwater biodiversity.


Through the above introduction and classification, you can have a more systematic understanding of the distribution and evolution of freshwater fish in modern animal systems, and appreciate their important significance in ecosystems and human society. If you need to further understand specific families, genera or species (such as morphological characteristics, distribution range, conservation status), it is recommended to refer to professional ichthyology books, regional freshwater fish atlases and the latest academic research literature. I hope this "Freshwater Fish Classification Encyclopedia" can meet your needs.

Marine fishs Freshwater fish Cypriniformes Siluriformes
Cyprinus carpio

Cyprinus carpio

Cyprinus carpio

Features:Physical fitness, colorful, changeable pattern, swimming style

Koi (Cyprinus carpio haematopterus) is a kind of high-grade ornamental fish popular in the world today, and has the reputation of "living gems in the water" and "art that can swim".Koi is an omnivorous fish. It can be eaten by mollusks, fragments of higher aquatic plants, benthic...

Trachidermus fasciatus

Trachidermus fasciatus

Trachidermus fasciatus,Four-gilled perch, flower drum fish, wife fish

Features:Looks like a tadpole

Songjiang perch (scientific name: Trachidermus fasciatus) is a fish of the family Sculpinidae and the genus Trachidermus, with no subspecies.Because the production of Songjiang near the mouth of the Yangtze River in China is relatively high and the body is relatively black, it is named Songjiang per...

Thymallus yaluensis

Thymallus yaluensis

Thymallus yaluensis, speckled trout

Features:There is a large red or yellow spot on the center of the body and the caudal peduncle, and 85 to 96 scales on the lateral line.

Yalu River grayling, whose Latin name is Thymallus yaluensis, is the most common grayling on the market. It has taken advantage of a loophole in the list, but it also belongs to a gray area.The Yalu River fennel and the Heilongjiang fennel have certain differences in morphology (maxilla and gill rak...

Thymallus arcticus grubei

Thymallus arcticus grubei

Thymallus arcticus grubei,Amur grayling, spotted trout, redfish, sea urchins, etc.

Features:The dorsal fin is long and tall in the shape of a flag. The back and sides of the body are purple-gray, with many small dark brown spots scattered on the sides of the body.

The Latin name of Heilongjiang grayling is Thymallus arcticus grubei, and its foreign name is Amur grayling. In the Heilongjiang and Yalu River systems, Heilongjiang grayling is the main target of local fishing.Heilongjiang grayling is a cold-water fish, but unlike other cold-water fish, they live i...

Arctic grayling

Arctic grayling

Thymallus arcticus

Features:The dorsal fin is tall, with a rounded, sail-shaped upper edge and up to 17-25 rays.

Arctic grayling (scientific name: Thymallus arcticus): is an animal of the family Thymallus and genus Thymallus.Arctic grayling may move tens of kilometers seasonally or annually between spawning, feeding, and sheltering habitats. Some Arctic grayling are known to travel more than 160 kilometers in...

Stenodus leucichthys nelma

Stenodus leucichthys nelma

Stenodus leucichthys nelma,Whitefish, Whitefish

Features:Similar to salmon, but with underdeveloped teeth, a small mouth, large round scales, dark grey back and white belly.

Stenodus leucichthys nelma belongs to the genus Stenodus of the family Salmonidae in the order Salmoniformes. In my country, it is mainly distributed in the waters below Burqin in the Irtysh River in Xinjiang. In the 1960s, it was the main target of fishing in the Irtysh River.In the lower reaches o...

Salvelinus malma

Salvelinus malma

Salvelinus malma,Hanazato Yoshiko

Features:Can go without food for almost a year

Salvelinus malma is a fish of the genus Salmonidae, with a body color ranging from brown to gray. The malma trout has a wide diet, mainly benthic animals (mainly mollusks) and insects that fall into the water, and sometimes even jumps out of the water to prey.There are two types of char: landlocked...

Hucho taimen

Hucho taimen

Hucho taimen,Zheluo fish, Taimen salmon, Zheluo green fish (Northeast China), big red fish (Xinjiang)

Features:It is one of the most ferocious freshwater fish.

Taimen (scientific name: Hucho taimen) is a cold-water carnivorous freshwater fish of the family Salmonidae and the genus Hucho.Taimen spends most of its time in fast-flowing streams, hibernates in deeper waters such as major rivers and lakes in winter, and migrates to streams in spring to spawn. Ta...

Hucho bleekeri

Hucho bleekeri

Hucho bleekeri,Sichuan Taimen, Bailey Taimen, Tiger Fish, Catfish

Features:It is the only surviving Taimen salmon on the Qinghai-Tibet Plateau.

The Latin name of Sichuan-Shaanxi Taimen is Hucho bleekeri. It is the southernmost (29-33°N) species among the five Taimen species in the world.Sichuan-Shaanxi Tailer is a cold-water fish that likes to live in deep river bays and flowing water environments, with gravel or sandy bottoms and mountain...

Brachymystax lenok(Pallas

Brachymystax lenok(Pallas

Brachymystax lenok(Pallas,Qinling Slimy Salmon

Features:It is a remnant species that migrated from the north to the south during the Ice Age.

Brachymystax lenok (Pallas,) is a relic species that migrated from the north to the south during the Ice Age and is a cold-water foothill fish.Brachymystax lenok feeds actively all year round. It mainly feeds on invertebrates, small fish, etc., and also preys on frogs and small rodents. It is extrem...

Bagarius yarrelli

Bagarius yarrelli

Bagarius yarrelli,Eagle tank, tank duckbill, eagle duckbill, papaya fish

Features:One of the most powerful fish in the order Siluriformes

The Latin name of the giant yarrelli is Bagarius yarrelli, which belongs to the order Siluriformes, family Scyphidae, and the genus Scyphus.The food is mainly small fish. It is slow-moving and greedy, and can be caught with a dragnet or sinking hook. Individuals are large, weighing more than 50kg. T...

Bagarius rutilus

Bagarius rutilus

Bagarius rutilus

Features:The name comes from the orange color of its pectoral fins, which resembles a giant bream in appearance.

The name of the red mullet comes from the orange color on its pectoral fins, not because it is produced in the Red River.The red mullet is ferocious and predatory. It mainly feeds on small fish, frogs and shrimps. It breeds around May to June.The biggest difference between the red catfish and the gi...

Bagarius bagarius

Bagarius bagarius

Bagarius bagarius,Yellow croaker, yellow croaker

Features:The head and front of the body are particularly thick and flat, with the dorsal margin at the starting point of the dorsal fin being the highest point of the body and gradually decreasing in depth. The caudal peduncle is round and the ventral surface is flat.

The Latin name of the fish is Bagarius bagarius, which is one of the species of the genus Bagarius in the family Siluridae of the order Siluriformes of the class Actinopterygii. It is commonly known as the melon fish.The fish is a carnivorous fish, fierce and predatory. It feeds on mollusks and smal...

Glyptosternum maculatum

Glyptosternum maculatum

Glyptosternum maculatum,Stone flat head

Features:The body surface is smooth and scaleless, the body is elongated, and the ventral surface is flat

It is the species with the highest distribution altitude among the family of fish, and can be found in waters with an altitude of about 4,500 meters.The black-spotted yao mainly lives in rock crevices and feeds on insect eggs or young fish. The number of chromosomes of the black-spotted protist is 2...

Euchiloglanisdavidi(

Euchiloglanisdavidi(

Euchiloglanisdavidi(, Stone Climber

Features:The body is elongated, the head is flat, and the length of the head is about the same as the width of the head

The Latin name of the bluestone catfish is Euchiloglanisdavidi (Sauvage, 1874), which is a fish of the genus Euchiloglanis of the family Euchiloglanidae.The bluestone catfish is a freshwater bottom fish. It is not very active and lives in the caves of rapids, clinging to the stone with its suction c...

Gagata dolichonema

Gagata dolichonema

Gagata dolichonema

Features:The body is long and flat, with narrow dorsal side and wide and flat head and trunk ventrally. The head is flattened laterally and the bone ridges are covered with thin skin.

Latin scientific name of filament black HeiGagata dolichonema,<span style ="background-color: rgb(255, 255, 255); color: rgb(51, 51, 51); font-family: "Helvetica Neue", Helvetica, Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQu...

Liobagrus kingi

Liobagrus kingi

Liobagrus kingi

Features:The adipose fin is connected to the caudal fin with a notch in the middle

King's mullet (Liobagrus kingiTchang,1935) is an animal of the genus Liobagrus in the family Amblycephalus.King's mullet is a small fish that likes flowing water and mainly feeds on aquatic insects and small fish and shrimps.Listed in the second level of the "List of National Key...

Pangasius sanitwongsei

Pangasius sanitwongsei

Giant catfish, Genghis Khan fish

Features:It can grow up to 300 cm long and weigh 300 kg, making it one of the largest catfish in the world.

The Genghis Khan fish is a native fish species of the Mekong and Chao Phraya rivers in Southeast Asia. It is a large carnivorous fish and the most ferocious fish in the entire Mekong and Chao Phraya rivers. It mainly feeds on crustaceans and fish. They are migratory. They usually spawn before the mo...

Silurus mento

Silurus mento

Silurus mento,Kunming-lakecatfish,Dianchi catfish

Features:The body is light yellow, the abdomen is grayish white, and there are irregular spots on the sides of the body.

Kunming catfish (scientific name: Silurus mento), foreign name Kunming-lakecatfish, belongs to the genus Silurus of the family Siluridae of the order Siluriformes, and is endemic to China.Kunming catfish is a carnivorous fish that likes to live in lakeshores with abundant aquatic plants. It hides at...

Mystus guttatus

Mystus guttatus

Mystus guttatus,Sesame, plum blossom, sea bream, sesame sea bream, white-bearded sea bream

Features:Looks like a catfish, once the "king of freshwater"

Mystus guttatus is a species of the genus Mystus in the family Myscidae. It is also called shad, sesame shad, white-bearded shad, and swordfish and pliers in rural Guangdong. It is large in size, with common individuals weighing 1-2 kg, and some large ones weighing 5-10 kg, and the largest can reach...

Yaoshania pachychilus

Yaoshania pachychilus

Yaoshania pachychilus,Panda fish, panda shark, golden band panda climbing rock loach

Features:Its body is distinctly black and white, like a small panda in the water.

The scientific name of the thick-lipped loach is Yaoshania pachychilus (Chen, 1980), a species of fish in the genus Yaoshania of the family Cyprinidae.Thick-lipped Protostomus was discovered by Academician Chen Yiyu in Dayao Mountain, Guangxi, China in 1980. At that time, it was classified under the...