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Toothy Tetras

For advanced freshwater aquarists looking for a challenge, the aggressive, buck-toothed Exodon paradoxus makes a good subject for a single-species tank.

By David A. Lass |

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When I was a kid, “The Innes Book” was one of three books I had on tropical fish. My 1955 copy was my most cherished possession, and I would page through it nightly. The Exodon paradoxus page always fascinated me. Exodon paradoxus is the only fish in its genus. It is a characin, which puts it in the same family as most of our tetras (and piranhas). In addition to being in its own genus, E. paradoxus is one of only a few fish that still has the same original scientific name that was first given to it. In the case of this fish, I would imagine that this is simply because it is not worth the time of ichthyologists to bother with trying to reclassify it. Ichthyologists today enjoy splitting or lumping (reclassifiers of fish are either “splitters” who break up genera into new ones, or “lumpers” who take different genera and lump them together) fish with existing names. There is no opportunity for either with a fish that is in its own genus.

The natural habitat of E. paradoxus is the Amazon River Basin in Brazil and Guyana, and they occur in schools, primarily in shallower waters. The fish gets to be 3 inches or so and is a silvery-yellow color. There are two large black spots on the sides of the body, the larger one just in front of the dorsal fin, the smaller one at the caudal peduncle (where the tail meets the body). The dorsal and tail fin are red, with a hint of red on the other fins.

Want to read the full story? Pick up the October 2010 issue of Aquarium Fish International today.

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