An old school tetra with new school appeal and heaps of colour. What’s holding you back?
WORDS: NATHAN HILL
AS MAINSTREAM FISH go, the emperor tetras could be up there as the most majestic. Eye catching and alluring, it’s little surprise that they hold as much appeal to newcomers as they do to long-established aquarists. The difference, of course, is that the old guard generally know how to get the best out of them, but that needn’t be a guarded secret.
What we might call the ‘true’ emperor tetras belong to the genus Nematobrycon, and there are two species, both originating in Colombia—the widespread but common emperor tetra, Nematobrycon palmeri, and the pricier but more indulgent rainbow emperor tetra, Nematobrycon lacortei. Historically it was thought that there was a third member of the genus, Nematobrycon amphiloxus, but this turned out to be the same fish as N. palmeri, and the name became a synonym. You’ve likely also seen another tetra traded under the ‘emperor’ moniker—the blue emperor tetra, Inpaichthys kerri, but that’s a very different fish from a different location (it’s Brazilian) and not one we’re looking at today.
The emperor tetra has a long history in the hobby, being introduced to it some 60 years ago by William Kyburz, although it was formally described much earlier, in 1911.
Since then, it has become something of a staple, in and out of fashion but rarely given the spotlight it deserves. Its more attractive cousin joined the fray a decade later, with N. lacortei being described in 1971.
Part of what makes Nematobrycon so charming is the obvious difference between the males and females, something that even newcomers can spot in a heartbeat. The most obvious sign is found in the tail, where adult males sport a tell-tale ‘lance’ of a fin extension on the trident-shaped tail, between the two normal lobes. No such extension is found on a female.
Beyond the fins, other striking differences present themselves. Look to the other end of the fish and regard the eyes. In N. palmeri, males possess blue irises, while the females possess yellow (in some exquisite specimens, this can even appear a rich gold). For N. lacortei, the male iris is intense ruby red, while the females have blue/green irises.
In aquaria
Appearance is one thing, but how about behaviour? Here, both species are mostly excellent,
with only scattered reports of trouble. As a community fish, most emperors seem mostly
well behaved most of the time. I’ve witnessed maybe a dozen nips and as many close
calls in decades of working with them, but even then, these seemed more inquisitive
than aggressive. The flowing fins of f
