Cuiu-Cuiu - Pre-historic fish of the Amazon

In the Amazon, there are some truly enormous fish that can intimidate even the most experienced fisherman or aquarist. The Oxydoras niger, or Cuiu-Cuiu, is a huge black-brown catfish that is perhaps the most pre-historic looking of Amazon fish. This catfish is also called a “black doradid”and remains one of the favorite large cats of aquarium keepers.

 The Cuiu-Cuiu grows up to 3 feet long (though 2 feet is average) and can weigh over 40 pounds. This catfish has a thick, leathery, black skin with sharp thorns jutting from the sides of their bodies, called scutes. This fish looks like a moving armored vehicle when it sifts through the bottom of the Amazon, looking for snails and insects to feast on. The Cuiu-Cuiu’s diet is mostly insects, snails, earthworms and berries from overhanging trees.

The Cuiu-Cuiu prefers soft water and has some of the best tolerance to temperature change in the Amazon. The Cuiu-Cuiu can tolerate temperatures as low as 10 degrees celsius, and as high as 30. As a result of its inherent hardiness, this catfish can live up to well over 10 years, which is substantial in the Amazon. The Cuiu-Cuiu’s tolerance to such temperatures also makes it a perfect survivor during the dry season when water temperatures soar as they drop very low under the hot equatorial sun.

The Cuiu-Cuiu is another Amazonian fish that takes on a yearly migration in the name of finding a mate and spawning. Like the Jaraqui, the Cuiu-Cuiu swims many miles to reach selected spawning sites where many Cuiu-Cuiu gather. The actual breeding process is still largely unknown in this species, but if this catfish behaves like other catfish, then the Cuiu-Cuiu probably makes a nest where the male guards the eggs until the fry are old enough to venture out on their own. No breeding has occurred in captivity and it’s very hard to tell the male from female apart.

Locals only rarely use this catfish as part of the diet. Not much of this fish is exported, so the Cuiu-Cuiu’s numbers aren’t threatened by over-fishing. This catfish is susceptible to many nematode parasites, which makes it dangerous to eat without proper cooking.

This catfish is so hardy that small populations of it have been found as far north as Florida. Of course, these populations came from former aquarium inhabitants that were set free. In larger numbers these catfish can compete with natural wildlife for resources and harm the delicate biological cycle of Florida’s wetlands.

 In fish stores, the Cuiu-Cuiu is sold as a 2-4 inch specimen that looks almost like a plecostomus. Beginning fish keepers don’t understand the immense size this fish can reach, as it often outgrows its tank.  Having too small a tank is dangerous because this strong cat can literally burst the sides of a tank that’s not built to withstand its swimming or darting.

Another interesting feature of this catfish is that it will “talk” to other catfish. The Cuiu-Cuiu will emit a low croaking sound. At night, locals can often hear this fish emitting this noise which is easily mistaken for a toad. This fish also makes this noise when it feels threatened or when it’s being handled. The Cuiu-Cuiu can also grind its dorsal fin against the socket where it connects to its body, producing a very distinctive grinding sound.

Photos copyright: Fishing-khaolak.com and Seriouslyfish.com