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Exodon paradoxus

  (Müller and Troschel, 1844)

A monotypic species

Bucktoothed Characin








The common name fits well with this species going by the structure of the teeth. This is not a community fish and does not do well even in a shoal of its own kind. The fish is often purchased by aquarists as a tank mate for a piranha. This might be because The Piranha Book (Myers 1972) depicts a population of this fish as if to imply the fish can live with piranhas. There are other books as well that use Exodon paradoxus as a suitable tank mate for piranhas. That is not a good idea, the E. paradoxus is a food source for piranhas. Placing an E. paradoxus, especially a large one with a small school of juvenile piranhas could lead to disaster since these fish are notorious scale eaters and could kill your young piranhas. As piranhas mature, E. paradoxus is a primary food for piranhas.


Exodon paradoxus is fairly abundant throughout the entire Amazon basin, including the rio Branco drainage in Guyana. The abundance of this species can be attributed to its peculiar ecology (rivers with sandy bottoms, mostly in savannah regions. The genus Exodon is closely aligned in this ecology with the freshwater puffer Colomesus asellus. The mouth of E. paradoxus is terminal and scarcely oblique; its premaxilla, which has an ascending process, has 3 outer tusks and 6 inner acute; the maxilla bears a tubercle near its joint and 9 or 10 acute teeth, the latter ones pointing outward. The mandible has 4 external tubercles, the foremost one pointing forward, and an inner series of about 17 small conical teeth of the characid type. The fish stomach contents when dissected of wild caught specimens consist of piles of partly digested scales from other fishes. They grow to 3 inches or more in the aquarium. Wild caught average 12.5 cm SL.


Copyright. Do not use outside of OPEFE without permission.

Copyright. Do not use outside of OPEFE without permission.




Exodon paradoxus are little fish with brilliant coloration. The caudal fin is yellow and the other fins are red to red tinting. Two very large dark spots, one in the humeral area in front of the dorsal fin level and the other one covering the whole height of the caudal peduncle are the main characteristics of this species. The species is meant for a species tank limited to a small shoal and should not be intermixed with other species.




The fish has been bred in captivity at 2 1/2 inches. Females are broader and heavier than the male. Males have a slightly longer anal and dorsal fin rays than the females. The dorsal, anal, and pelvic fins are reddish, adipose yellow, caudal yellowish basally, lobes pink; back brownish, silvery ventrally, tinted yellowish. The female is generally yellowish. The species was first bred in captivity in 1955 by a 17 year old named Martha Tutwiler. According to Tutwiler, breeding this species is difficult, because of the fast swimming nature of the species. They were fed live foods and were constantly eating. The species are fin-nippers and recommended no other species be kept with them. The spawning took place in a ten gallon aquarium densely filled with artificial spawning grass (Spanish moss). There were only two inches of clear water above the plants. The breeders swam back and forth releasing eggs and eating them as they fell. Miss Tutwiler, assumed that if they had been provided a larger aquarium she would have been able to save more of the eggs. The fry hatched from the eggs in about 48 hours at 74°F. Breeders must be removed after spawning.




Amazon River basin and Tocantins River basin: Brazil and Guyana



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UPDATED: 12/05/2015