The genus Gymnotus has undergone considerable taxonomic revision in recent years, with over 20 new species being described since 1994, of which this stunning species is one. It's still very rare in the hobby and tends to command a high price when available. Like other Gymnotids, it produces a weak electric field using specially-adapted muscle tissue located towards the tail. It also possesses electroreceptors which allow the fish to receive electrical signals. With these the fish can sense …

Not a good beginner's species, due to its very respectable adult size, but it makes a stunning oddball addition to communities of larger fish. It's sensitive to many aquarium medications, particularly those containing copper.

The genus Gymnotus has undergone considerable taxonomic revision in recent years, with over 20 new species being described since 1994, including several that were originally considered to be G. carapo. The systematics of the genus are still not fully understood…

One of the most notorious fish in the world, the electric eel is a truly fascinating species. Its vital organs are contained in the front portion of the body, with up to 80% of it being reserved for the enormous electricity-producing organs. It uses electricity in several ways. The species is nocturnal and has very poor eyesight and so uses a weak electric field to navigate and identify its surroundings. This weak, pulsing signal is produced by the Sachs organ, one of 3 electricity-producing org…

T. stellatus is superficially similar to its only congener T. securis, but can immediately be identified by the presence (vs. absence) of a prominent dark spot in the dorsal-fin. It is sometimes traded as ‘platinum hatchetfish’.

The genus Thoracocharax was originally erected by Fowler in 1906 as a subgenus of Gasteropelecus, but was elevated to generic status by Weitzman (1960).

This species spends almost all of its time at or just below the water surface, although it will sometimes retreat into midwater if threatened or feeding. Like other freshwater hatchetfishes, it is renowned for its ability to leap from the water surface and glide for distances of several metres. This behaviour is used both to catch flying insects, and to escape potential predators.

Gasteropelecids are commonly-referred to as ‘freshwater hatchetfishes’ due to their heavily-keeled body shape which has evolved in such a way due to possessing an enlarged, heavily-muscled pectoral girdle, and which resembles the shape of a hatchet head.

They are sometimes said to be capable of propelled flight above the water surface by beating their pectoral fins but in fact this is not the cas…

C. strigata is an enduringly popular species in the aquarium hobby but is not bred on a commercial basis with all fish offered for sale collected in the wild.

It can be told apart from other members of the genus by its larger adult size and dark, marbled colour pattern appearing as a series of dark and light stripes running diagonally across the body below the lateral line.

This colour pattern is variable and popul…

Also known as the golden trahira, H. unitaeniatus is the only one of the three recognised species currently in the genus to appear in the trade with any regularity. It's really a fish suitable only for the specialist, and as with any predatory species, care must be taken when performing tank maintenance.

It's a representative of an ancient group of fishes, and possesses a modified, highly vascularised swim bladder that acts as an accessory breathing organ, allowing the fish to survi…

A species for the specialist, E. erythrinus is also known as the rainbow wolf fish or red hi-fin wolf fish. It is quite variable in colour and pattern depending on collection locality. There is a variant from Peru that has a bright orange belly. Recent studies have highlighted genetic differences in these different populations, suggesting that E. erythrinus is actually a species complex, rather than a single species. There is currently one other recognised species in the genus, E. kessleri, but …

This species is now considered a member of the Hara genus by many experts, but as things stand it is still officially included in Erethistes. It is, in all likelihood, a Hara, as Erethistes is characterised by divergent denticles on the pectoral fins, whereas Hara possess outwardly pointing denticles. E. maesotensis has these outwardly pointing denticles.

It's quite rare in the trade, but makes an interesting addition to an Asian stream community tank if you can get hold of some….