Freshwater fish may be either coldwater or tropical species. Although freshwater aquariums can be set up as community tanks, coldwater and tropical fish are generally not mixed due to incompatibilities in temperature requirements. Tropical freshwater aquariums house "warm water" fish such as cichlids, tetras and other species that require a heating apparatus. For a tropical fish tank, maintaining a warm environmental temperature ranging between 75 to 80 °F (24 to 27 °C) enables the fish to thrive.

The major families and species include:

Algae eater is a common name for many bottom-dwelling fish that feed on algae.

The guppy (Poecilia reticulata), also known as the millionfish, is one of the most popular freshwater aquarium fish species in the world.

Arrowanas are freshwater bony fish of the family Osteoglossidae, also known as bonytongues.

Invertebrates are animal species that do not develop a vertebral column. This in effect includes all animals apart from the subphylum Vertebrata.

Barbs are a "schooling" fish -- which means they prefer to hang out in a group of other barbs.

Killifish is captive bred, but is normally found in freshwater and brackish ponds, streams and marshes of Africa.

Fresh Water Barracudas are predators that eat fish that will fit into their mouths.

Aside from the electric eel (Electrophorus electricus), Gymnotiformes are slender fish with narrow bodies and tapering tails, hence the common name of "knifefishes".

The betta was first discovered in Southeast Asia.  Making its home in rice paddies, drainage ditches and the warm flood plains of the region, the betta became accustomed to frequent storm flooding and devastating droughts.

Leporinus fasciatus commonly known as the banded leporinus or the black-banded leporinus is a species of characin in the family Anostomidae.

Botia is a freshwater fish in the loach family (Botidae).  It was a large genus with about 20 species. The fish in these genera possess a pair of razor-sharp spines under their eye sockets.

Most of the loaches are not very large, being only a few inches, but there are exceptions with a few of the Botia reaching over 12" (30 cm) and the exceptionally large Royal Clown Loach which can reach up to 20" (50 cm).

The freshwater butterflyfish or African butterflyfish (Pantodon buchholzi) is the only species in the family Pantodontidae.

A small genus of small to medium-sized, South American freshwater fish closely related to the piranha and often referred to as silver dollars, Metynnis have been known to the aquarium trade for decades.

Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior.

Mollies (Poecilia) are a genus of fish that are native to fresh, brackish and salt water in the Americas. Live-bearers, the Poecilia species are collectively known as mollies.  

Cichlids span a wide range of body sizes, from species as small as 2.5 centimeters (0.98 in) in lengthto much larger species approaching 1 meter (3.3 ft) in length.

The family Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are freshwater fish in the orderOsteoglossiformes native to Africa.

Members of the South American Corydoras are freshwater temperate and tropical catfish in the armored catfish family, and are commonly referred to as corydorases, corries or cory catfish.

Platy is a common name for two related species of freshwater fish in the genus Xiphophorus. Both species are livebearers, similar to other fish of the family Poeciliidae, such as the guppy and molly.

The Danio genus comprises many of the species familiar to aquarists. The common name "danio" is used for members of the genera Danio.

Hypostomus plecostomus (known colloquially as a sucker fish) is the scientific name for a type of freshwater tropical Central and South American fish belonging to the family Loricariidae.

Discus is a genus of cichlids native to the Amazon River basin. Discus are popular as aquarium fish and their aquaculture in several countries in Asia is a major industry.

Adult Tetraodon nigroviridis are found in freshwater streams, rivers, and flood plains; young are found in brackish water.  It is also found in mangrove forests. 

Freshwater eels are elongate with tubelike, snake-shaped bodies.

The rainbowfish are a family of small, colourful, freshwater fish that are found in northern and eastern Australia, New Guinea, islands.

Hogchokers are sometimes offered for sale in aquarium stores, often marketed as "Freshwater Flounder".

Freshwater aquarium sharks aren’t actually sharks at all. Most freshwater shark species are actually barbs or minnows and are called sharks due to the shape of their bodies.

Gar bodies are elongated, heavily armored with garnoid scales, and fronted by similarly elongated jaws filled with long, sharp teeth.

Freshwater stingrays are Neotropical freshwater fishes of the Potamotrygonidae family (order Myliobatiformes).

The GloFish is a patented and trademarked brand of genetically modified (GM) fluorescent fish.

The Swordtail is a live-bearing fish related to freshwater aquarium favorites including guppies, mollies, and platys. The Swordtail is an omnivore that will eat commercially prepared flaked foods and algae as well as freeze dried bloodworms, tubifex, and brine shrimp.

The gobies, family Gobiidae, are among the most speciose fish families, with more than 2000 species in 200 genera worldwide and a long taxonomic history.

A tetra is one of several species of small freshwater fish fish from Africa, Central America and South America belonging to the biological family Characidae and to its former subfamilies Alestidae (the "African tetras") and Lebiasinidae.

Gourmies are a family, Osphronemidae, of freshwater perciform fishes. The fish are native to Asia, from Pakistan and India to the Malay Archipelago and northeasterly towards Korea.