Below is a list of some of the most commonly known fish that could be suitable to have in an aquarium tank, along with a few of their most basic characteristics.

Cichlids
These fish belong to the Cichlidae family and they are one of the most popular freshwater fish that can be kept in an aquarium tank. Their body size can range from only a couple of centimetres to a metre. This family is primarily herbivorous, consuming mainly algae and plants, with only a minor part of their diet being small invertebrates. Among some of the most popular species we can find:

Angel fish Pterophyllum scalare
Temperature range:  24-28oC
pH range: 6.0-7.5
Distribution:    Central America
Diet:     Omnivorous; most commercial foods, some vegetables such as lettuce
Size:    up to 15 cm
Characteristics:    Middle swimmer
Remarks:  prefers a soft water, planted tank.  Angels will eat smaller fish, not keep with neon tetras and similar sized species.

Discus  Symphysodon spp.
Temperature range: 26-30oC
pH range:   6.0-6.5
Distribution:  Amazon
Diet:  Carnivorous; small live foods, frozen food, flake foods
Size:  up to 15 cm
Characteristics:  Middle to bottom swimmer
Remarks:  Prefers a tall, planted tank with soft, acidic water.  Require non aggressive companion fish or species tank.  Water conditions important, high rate of filtration required.

Oscar Astronotus acellatus
Temperature range: 22-25oC
pH range:  6.0-8.0
Distribution: South America
Diet:  Carnivorous; meat, earthworms, frozen and pelleted food
Size: up to 25 cm
Characteristics:  Middle swimmer
Remarks:  Rapid growth rate, prone to digging up substrate, best kept with other large fish or in a species aquarium, tolerant of a wide range of water conditions

Kribensis  Pelvicachromis pulcher
Temperature range:  24-25oC
pH range: 6.5-7.5
Distribution:  Africa
Diet:  Omnivorous; flake, frozen and live food, bloodworm
Size:  up to 12 cm
Characteristics:  Middle to bottom dweller
Remarks:   Needs a well planted aquarium with hiding places, caves and rocks.

Others are:
Keyhole Cichlid Cleithracara maronii
Firemouth Cichlid Cichlasoma meeki
Swallowtail Cichlid Aulonocara carolinae
Orange Chromide Etroplus maculatus


Livebearers
Among the most common ones are those of the family Poecilidae.  These types of fish are mainly referred to as those that give birth to live, free-swimming young, within which we can include:

Black Molly and Mexican Molly Poecilia sphenops
Temperature range:  18-28oC
pH range:  7.0-8.5
Distribution:  Mexico
Diet:  Omnivorous; flake and green foods
Size:  up to 7 cm
Characteristics:  Middle swimmer
Remarks:  Live bearer that is easy to breed, prefers a hard water with some salinity and planted aquarium.  Peaceful species suitable for community aquarium with similar fish.

Guppy Poecilia reticulata
Temperature range:  22-28oC
pH range:  7.0-8.5
Distribution: Central America
Diet:  Omnivorous; flake, frozen and green foods
Size:  up to 5 cm
Characteristics:  Middle swimmer
Remarks:  Livebearer, easy to breed, can produce up to 30 young every 3 weeks, prefers a well planted tank.  Other species may nip the long fins of guppies so are more suited to a species tank.

Platy Xiphophorus maculatus
Temperature range:  20-26oC
pH range:  7.0-8.0
Distribution:  Mexico
Diet:  Omnivorous; live, frozen, flake and green foods
Size:  up to 6 cm
Characteristics:  Middle swimmer
Remarks: Livebearer, easy to breed, easy fish species, hardy and a good fish for peaceful community aquariums.  Available in a range of colour forms.

Others are:
Swordtail  Xiphophorus helleri
Variatus Platy  Xiphophorus variatus


Loaches
These are fish families of the order Cypriniformes, which is considered one of the largest groups of freshwater fish. Loaches have mostly a thin ell-like body and they like to hide and sneak for food on the bottom of the tank. In nature, they can be found in areas surrounded by plants and they are known to be nocturnal.

Coolie Loach Pangio Kuhli
Temperature range:  24-30oC
pH range:  6.0-6.5
Distribution:  Southeast Asia
Diet:  Omnivorous; live, frozen or tablet food, small worms.  Feed at night.
Size:  up to 12 cm
Characteristics:  Bottom dweller
Remarks:  Prefers soft, acidic water and a well planted tank with plenty of hiding places; needs low light or shaded conditions. 

Others are:
Clown Loach Chromobotia macracanthus
Java Loach Pangio oblonga


Anabantids
This type of fish belongs to the Order Labyrinthici, characterised by their breathing apparatus, the “labyrinth”. These fish have the ability to grasp oxygen from the surface of the water, gulp the air and pass it through this specialised breathing organ, allowing some of them to survive out of the water for a longer period of time than most other fish (as long as they remain moist).

Siamese Fighting Fish Betta splendens
Temperature range:  24-29oC
pH range:   6.0-8.0
Distribution:  Thailand and Cambodia
Diet:  Omnivorous; live or frozen and flake foods
Size:  up to 8 cm
Characteristics:  Middle to top swimmer
Remarks:  Highly aggressive species, males will fight to the death, males are best keep alone as other fish will nip at the long flowing fins.  Females are more peaceful but lack the colouration and long fins of the males

Dwarf Gourami Colisa lalia
Temperature range:  22-28oC
pH range:  6.5-7.5
Distribution:  India
Diet:  Omnivorous; Daphnia, bloodworms, live or frozen, flake food and vegetables
Size:  up to 6 cm
Characteristics:  Middle to upper swimmer
Remarks:  Keep with other peaceful community fish, requires high water quality and may be prone to disease.    Plant material required when breeding.

Kissing Gourami Helostoma temminckii
Temperature range:  22-28oC
pH range:  6.5-8.5
Distribution:  Thailand
Diet:  Omnivorous; flake, frozen foods and vegetables
Size:  up to 16 cm
Characteristics:  Middle swimmer
Remarks:  Kept for their `kissing’ action with is a display of strength between males.  Adaptable to a wide range of water conditions, will eat many plants.  Can be kept with similar sized fish.

Others are:
Pearl Gourami Trichopodus leerii
Three-spot Gourami Trichogaster trichopterus


Catfish
This type belongs to the order of the Siluriformes, being the genus Corydoras particularly popular within the aquarium hobbyist. Catfish are nocturnal fish and are primarily bottom feeders, and they all have a common characteristic of possessing whisker-like prominent barbels.

Bristlenose Catfish Ancistrus spp.
Temperature range:  22-25oC
pH range:  6.5-7.5
Distribution:  South America
Diet:  Herbivorous; algae, vegetables, algae tablets, bogwood for rasping
Size:  up to 12 cm
Characteristics:  Bottom dweller
Remarks:  Requires plenty of vegetable food and bogwood which forms part of the diet.  Males may be territorial and will use their spines against other males.  Suitable for a well planted, community aquarium.

Plec   Hypostomus plecostomus
Temperature range:  20-28oC
pH range:  6.0-8.0
Distribution:  South America
Diet:  Omnivorous; vegetables, flake and frozen food, algae tablets
Size:  up to 26 cm
Characteristics:  Bottom dweller
Remarks:  Hard, easy to care for fish which grows rapidly and needs a large tank for mature specimens.  Peaceful community species often purchased as an algae eater.

Glass Catfish or Ghost Catfish Kryptopterus bicirrhis
Temperature range:  22-26oC
pH range:  6.0-7.0
Distribution:  India
Diet:  Omnivorous; eats small insects, frozen and flake foods
Size:  up to 10 cm
Characteristics:  Middle to upper swimmer
Remarks:  This cat fish has a transparent body and is best kept in a school.  Requires good filtration and a moderate water flow with plenty of swimming space.  

Upside-Down Catfish Synodontis nigriventris
Temperature range:  22-26oC
pH range:  6.5-7.5
Distribution:  Africa
Diet:  Omnivorous; small insects, frozen and flake foods, this species turns upside down to feed.
Size:  up to 12 cm
Characteristics:  Middle to top swimmer
Remarks:  Peaceful community fish which is active at dusk.  Requires good quality water and filtration rates as it is prone to some diseases such as “white spot”.

Others are:
Dwarf Corydoras Corydoras elegans
Emerald Catfish Brochis splendens
Spotted Raphael Agamyxis pectinifrons
Striped Raphael Platydoras armatulus
Walking Catfish Clarias batrachus


Tetras
These small freshwater fish belong to the Characidae family, very popular and easy to keep in an aquarium. One of the characteristics that differentiate the majority of tetras from other fish is the presence of an adipose fin between the caudal and dorsal fins, which, along with the last unpaired fin (the anal fin) gives this fish its characteristic name “tetra”, meaning “four” in Greek.

Glowlight Tetra Hemigrammus eruthrozonus
Temperature range:  22-26oC
pH range:  5.0-7.0
Distribution:  South America
Diet:  Omnivorous; frozen, flake and pellet foods, live insect larvae
Size:  up to 4 cm
Characteristics:  Middle to top swimmer
Remarks:  Easy to care for, prefers, soft acidic water.

Neon Tetra Paracheirodon innesi
Temperature range:  22-26oC
pH range:  5.0-7.0
Distribution:  South America
Diet:  Omnivorous; flake and frozen food
Size:  up to 4 cm
Characteristics:  Middle to top swimmer
Remarks:  One of the most popular aquarium fish, best kept in schools for maximum display.  Easy to care for, hardy and can live as long as 8 years.

Bleeding Heart Tetra Hyphessobrycon erythrostigma
Temperature range:  22-26oC
pH range:  5.0-7.0
Distribution:  South America
Diet:   Omnivorous; flake and frozen food, live food
Size:  Up to 6 cm
Characteristics:  Middle to top swimmer
Remarks:  Males have long dorsal and anal fins and an attractive colour and should be kept with some of the lesser coloured females in a community tank.

Others are:
Black Tetra Gymnocorymbus ternetzi
Black Neon Tetra Hyphessobrycon herbertaxelrodi
Bloodfin Tetra Aphyocharax anisitsi
Cardinal Tetra Paracheirodon axelrodi
Congo Tetra Phenacogrammus interruptus
Diamond Tetra Moenkhausia pittieri
Head and Tail Light Tetra Hemigrammus ocellifer
Penguin Tetra Thayeria boehlkei
Red-Eye Tetra Moenkhausia sanctaefilomenae