Tetra- Bucktooth Tetra- Exodon

Do you fancy keeping a ravenous, flesh-crazed beast but lack the room? Maybe the Bucktooth tetra tips the scales your way suggests Nathan Hill.

South America is full of sharp-toothed, devil-fanged predators that would make even H P Lovecraft shudder. There are the piranha, freshwater barracuda and Tiger characins featured among other nasty pieces of work.

However, there are also more specialised kinds of carnivore — and that’s where Exodon paradoxes, the Bucktooth tetra, homes in.

This fish is not a predator in the technical sense. Rather, like the gill-munching candiru, Exodon is a parasite, eating away at its prey but not benefitting from its outright death. They choose to eat fish but strip off only the surface layer of skin. To be exact, they are scale eaters.

The lepidophage (scale eating) lifestyle is nothing new and not only Exodon exhibits it. In fact, there are at least another five South American characin genera that all scratch a living the same way. There are even cichlids that live this way — and that behaviour has independently evolved in at least 12 lineages.

Not for the community!

The way Bucktooth feed is a sight to behold and one of the reasons keepers are initially attracted to them. Offered a block or cube of food in the aquarium, they rapidly form a feeding ball, like bees swarming about a hive, with each fish dashing to the centre of the frenzy to get its share.

In the aquarium, Buckteeth are useless community fish. Tank mates are seen as swimming organic vending machines, there to be tucked into at any time until stripped down like corn off of the cob.

You’ll not turn that behaviour off either. Exod is as hardwired to eat scales as cockerels are to crow at dawn. Attempts to wean them solely onto flakes and bloodworms in the hope of ending their bloodlust are doomed.

Wild Buckteeth don’t just supplement their diet with scales, it’s the core of their menu. When analysed, wild fish are found to have an average of 88% scale in the belly, alongside about 10% terrestrial insects and the tiniest taste of green stuff.

These scale-feeding antics have even led to another morphological and behavioural trait – left or right-handedness.

Viewed from underneath, an Exodon head will permanently tilt ever so slightly to either left or right and this relates to the way they attack their victims. Left-handed (or mouthed) Buckteeth attack the right flank of other fishes, snapping at the scales before glancing away to the tail.

This is different to the way cichlids feed on scales. A cichlid will creep up from behind, at an angle, and glace forward, snatching a scale as it does.

The Bucktooths are far more gung ho, directly side-ramming their prey in a far more ferocious and direct attack.

They’ve even evolved special teeth for the job — hence the name. Their descaling, cuspidate dentition carries an extremely pointed tip for getting underneath that troubling outer layer of fish to yank away what’s beneath. They don’t even leave with a mere mouthful, instead tearing off scales and gorging on them as they sink and drift to the bottom.