Guppy, male (top); female (bottom)（Image source：Anton Melqkov， CC BY-SA 4.0 ） The guppy ( Poecilia reticulata ) is one of the most popular freshwater ornamental fish in the world. It is native to northern South America, including Venezuela, Brazil, Guyana, Trinidad, and Barbados. Because of its remarkable adaptability, the species has spread far beyond its native range and now inhabits many tropical and subtropical freshwater environments worldwide. In nature, guppies commo

Saddled bichir ( Polypterus endlicherii ) in the aquarium trade （ Image source ：elfsama， CC BY-NC 4.0 ） The saddled bichir ( Polypterus endlicherii ) is a member of the family Polypteridae within the order Polypteriformes of the class Actinopterygii. It is a predatory fish commonly seen in the aquarium trade. Because of its highly primitive appearance and body structure that differs markedly from most other bony fishes, it is often called a “dinosaur fish” in the aquarium m

Male green swordtail（Image source：Bastet78， CC BY-SA 3.0 ） The green swordtail ( Xiphophorus hellerii ) is a tropical ornamental fish. It is native to North and Central America, with its natural range extending from Veracruz in Mexico to northwestern Honduras, inhabiting rivers and streams throughout this region. Wild populations are typically found in fast-flowing waterways with dense vegetation, though they may also occur in canals and occasionally even in brackish enviro

Wild form of Poecilia sphenops （Image source：Dnoerholm， CC BY-SA 4.0 ） The molly ( Poecilia sphenops ) is a livebearing fish native to Mexico, Guatemala, and Honduras. Because of its attractive appearance and ease of care, it holds an important place in the global ornamental fish trade. In aquarium markets, the most commonly cultivated form of this species is the black molly. It is also frequently hybridized with related species such as the sailfin molly ( P. latipinna ) an

Guinean bichir（ Polypterus ansorgii ）drawing（Image source：Boulenger, George Albert， CC0 1.0 ） The Guinean bichir ( Polypterus ansorgii ) is a member of the family Polypteridae within the order Polypteriformes of the class Actinopterygii. It is a predatory species commonly found in the aquarium trade. Because of its primitive appearance and body structure that differs markedly from most other bony fishes, it is widely known in the aquarium market as a “dinosaur fish.” In Chi

Cardinal tetra（Image source：CHUCAO， CC BY-SA 3.0 ） The cardinal tetra ( Paracheirodon axelrodi ) is a highly popular ornamental fish belonging to the family Characidae within the order Characiformes. Species in the genus Paracheirodon are commonly referred to as “neon tetras.” These fish typically grow to about 2–3 cm in length. Although small, they are strikingly colorful, with a bright iridescent blue stripe running along the side of the body and a vivid red coloration c

Neon tetra（Image source：André Karwath， CC BY-SA 2.5 ） The neon tetra ( Paracheirodon innesi ) is a small yet brilliantly colored tropical ornamental fish belonging to the family Characidae. Members of the genus Paracheirodon are commonly known as neon tetras. They are native to the Amazon River basin in South America, inhabiting both blackwater and clearwater streams. Their distribution includes southeastern Colombia, eastern Peru, and western Brazil. These streams usually

Wild Southern platyfish（Image source：Marrabbio2， CC BY-SA 3.0 ） The Southern platyfish ( Xiphophorus maculatus ) is one of the most popular freshwater ornamental fishes and belongs to the family Poeciliidae. It is native to warm waters extending from southern Mexico to Belize and Guatemala. In the wild, it commonly inhabits slow-moving streams, drainage ditches, irrigation channels, and shallow sun-warmed waters. These habitats are typically rich in aquatic vegetation, orga

Symphysodon discus （Image source：Doronenko， CC BY 3.0 ） The discus fish, belonging to the genus Symphysodon , is a group of freshwater fish native to the Amazon River basin in South America and a member of the family Cichlidae. Their body shape is highly distinctive, forming a nearly circular disc that is laterally compressed and tall. Adult individuals typically reach about 12–15 cm in length, although some wild specimens may exceed 20 cm. Body coloration is highly variabl

Freshwater angelfish（Image source：mendel， CC BY-SA 1.0 ） The freshwater angelfish ( Pterophyllum scalare ) belongs to the family Cichlidae and is among the most popular freshwater ornamental fishes in the aquarium trade. This species originates from the Amazon Basin of South America and is widely distributed across several countries, including Peru, Colombia, and Brazil. It occurs in major tributaries such as the Ucayali River and the Solimões River, as well as in river sys

Goldfish（Image source：Ry362， CC BY-SA 3.0 ） Goldfish ( Carassius auratus auratus ) is an ornamental fish derived from a mutant lineage of the wild crucian carp ( Carassius auratus ) native to China. Through deliberate selective breeding and long-term domestication by humans, this lineage gradually developed into the ornamental form known today as the goldfish. Historical records indicate that people were already keeping these fish during China's Northern and Southern Dynast

Kohaku koi（Image source：Maxikoi， CC BY-SA 3.0 ） Koi ( Cyprinus rubrofuscus haematopterus ) are ornamental strains selectively bred from the East Asian carp ( Cyprinus rubrofuscus ). Wild carp are widely distributed throughout East Asia, inhabiting large river basins across China, Korea, Russia, Vietnam, and Laos. In the wild, these fish typically display subdued coloration, most often dark brown or black, which allows them to blend into the bottom environments of lakes, riv

Siamese fighting fish, male, selectively bred（Image source：NelsonNellie， CC0 1.0 ） The Siamese fighting fish ( Betta splendens ), commonly known as the Siamese fighting fish or betta, is a freshwater species native to Southeast Asia. Its natural distribution includes Thailand, Cambodia, Laos, Vietnam, Malaysia, and Myanmar. In the wild, these fish are most often found in rice paddies, marshes, shallow ponds, and densely vegetated wetlands. Because these habitats are typicall

Ram cichlid（Image source：Eric Mengel， CC0 1.0 ） The Ram cichlid ( Mikrogeophagus ramirezi ) is a dwarf cichlid species native to the Orinoco River basin of South America. It primarily occurs in the tropical savanna regions of Colombia and Venezuela, inhabiting warm, acidic stretches of slow-moving water. These waters often appear brown or black due to the decomposition of plant debris that releases humic substances into the environment. This species is relatively small in si

Glowlight tetra（Image source：gonzalovalenzuela， CC BY 2.0 ） The glowlight tetra ( Hemigrammus erythrozonus ) is native to the Essequibo River basin in Guyana, South America, including tributaries such as the Mazaruni River and the Potaro River. These waterways represent typical blackwater environments, where large amounts of fallen leaves, branches, and other organic matter decompose and release tannins into the water. As a result, the water appears tea-brown in color and r

Rummy-nose tetra（Image source：Brian Gratwicke， CC BY 4.0 ） The rummy-nose tetra ( Hemigrammus rhodostomus ) belongs to the family Characidae and is a small schooling fish native to freshwater rivers in South America. Adult individuals are relatively small, typically reaching only 4–5 cm in length. Their bodies are silvery white, the caudal fin displays striking black-and-white banding, and the most recognizable feature is the vivid red coloration on the snout and around the

Corydoras sterbai （Image source：Matthew Mannell， CC0 1.0 ） The genus Corydoras belongs to the family Callichthyidae and comprises a group of benthic freshwater fishes native to South America. More than 170 species have been described within this genus. Their distribution is remarkably broad, extending from the eastern slopes of the Andes to the Atlantic coast, and from Trinidad in the north to the Río de la Plata basin of northern Argentina in the south. Most Corydoras spe

Mokèlé-mbèmbé bichir（ Polypterus mokelembembe ）。(Image source： Ooi Hong Liang ， CC BY-NC 4.0 ) The Mokèlé-mbèmbé bichir ( Polypterus mokelembembe ) is a member of the order Polypteriformes within the class Actinopterygii. It belongs to the family Polypteridae and is a predatory fish commonly encountered in the aquarium trade. Because of its highly primitive appearance and body structure that differs markedly from most other bony fishes, it is widely referred to as a “di

Ornate bichir（ Polypterus ornatipinnis ）。（Image source： lapradei ， CC BY-NC 4.0 ） The ornate bichir ( Polypterus ornatipinnis ) is a member of the class Actinopterygii, order Polypteriformes, and family Polypteridae. It is a predatory fish commonly found in the aquarium trade. Because of its extremely primitive appearance and body structure that differs markedly from most teleost fishes, it is often referred to in the aquarium market as a “dinosaur fish.” In Chinese markets

Poll's bichir （ Polypterus polli ）（Image source： John P Friel ， CC BY 4.0 ） Poll's bichir ( Polypterus polli ) is a member of the class Actinopterygii, order Polypteriformes, and family Polypteridae. It is a predatory fish commonly found in the aquarium trade. Because of its strongly primitive appearance and body structure that differs markedly from most other bony fishes, it is often referred to as a “dinosaur fish” in the aquarium market. Morphology Like other members o