This species is not actually a piranha in ichthyologic terms, being monotypic and therefore unique. It was so named due to its general resemblance to true piranha, and the fact that it is quite closely related to Pygocentrus species. Mento means "chin", referring to the protruding jaw of the fish.

This jaw structure, along with the adapted teeth, is used in its natural feeding behaviour. It has been observed to swim at great speed into a selected target, biting hard as it collides w…

The tyre track eel is also referred to as the white-spotted spiny eel.

A member of the spiny eel family, which range across tropical Asia and Africa, Mastacembelus armatus is one of the more common species available to the hobby, along with the peacock eel ((Macrognathus siamensis)and the fire eel (Mastacembelus erythrotaenia). These species are all from Asia but there are some members of the family from Africa that are occasionally seen for sale. These majority of these species are from the …

A member of the spiny eel family, which range across tropical Asia and Africa, Mastacembelus erythrotaenia is one of the more common species available to the hobby, along with the peacock eel (Macrognathus siamensis)and the tyre-track eel (Mastacembelus favus). These species are all from Asia but there are some members of the family from Africa that are occasionally seen for sale. These majority of these species are from the Afromastacembelus genus, with the most common representative being the…

The genus Exodon is currently monotypic, with this single species having uniquely designed teeth. These allow it to rip the scales from other species. It's an ideal choice for those wishing to keep a large shoal of a predatory species without possessing the massive amount of tank space needed for a shoal of piranha or similar. A tank full of these makes for a very colourful and active display….

There are currently six described species in the genus Thalassophryne, of which T. amazonica is the only freshwater representative. The others (T. nattereri, T. maculosa, T. megalops, T. montevidensis and T. punctata) are all estuarine animals distributed along the western Atlantic coastlines of Central and South America and inhabit brackish-to-marine waters. They are members of the family Batrachoididae or toadfishes, of which most are exclusively marine species. All batrachoidids are ambush pr…

Lungfish are among the most intriguing of "oddball" aquarium subjects, being able to survive in the most extreme conditions. They are very ancient fish, having remained virtually unchanged for millions of years.

The natural habitat of P. a. annectens is wet for only part of the year and the fish has developed several incredible adaptations in order to counteract this. When the waters begin to recede, the fish will find a suitable nesting site, usually amongst heavy vegetation. Here…

Lungfish are among the most intriguing of "oddball" aquarium species, being able to survive in extreme conditions. They are very ancient fish, having remained virtually unchanged for millions of years. This is the only species known from South America, and is the sole representative of its genus. Most hail from Africa, with a single species native to Australia. They belong to the class Sarcopterygii (lobe-finned fishes), members of which are actually more closely related to terrestrial…

This is one of the largest freshwater fish species in the world, and clearly shouldn’t be considered a home aquarium subject at all given its eventual size and the fact it can live for well in excess of 50 years. We include it here only because some public aquaria are able to maintain it long-term.

Unfortunately, juveniles are seen for sale quite regularly in the aquari…

Known from Great Lakes Erie and Michigan with distribution extending south through the Mississippi River basin to the Gulf of Mexico drainages where it’s said to occur between the lower Apalachicola River in Florida and the Nueces River in Texas.

It may also be found in the Rio Grande which forms the border between Mexico and the United States further south where records include Falcon International Reservoir, for example.

This species is also referred to as ‘royal knifefish’ in the aquarium trade but arguably has no place in the ornamental hobby given its adult size and specialised requirements.

It can be distinguished from congeners by presence of many small, dark spots on the anterior portion of the body which merge to form oblique, irregular stripes extending onto the anal and caudal fins posteriorly.