Colin is confusing the real barracudas (
Sphyraena spp.) with the freshwater "barracuda" of the hobby, usually species of
Ctenolucius. While
Ctenolucius is a fairly common aquarium fish, I have yet to see any marine aquarium store selling
Sphyraena spp.
In any case,
Ctenolucius are gregarious freshwater fish that are mostly active by dusk and dawn. They're reasonably easy to keep given a big, quiet tank with lots of shade (floating plants or long Vallisneria leaves will do nicely). They do not combine well with aggressive tankmates. They are very shy and nervous, and have to be kept in groups of 5+ specimens and in a nice, big tank so they can't smash themselves up. Although they prefer live food such as earthworms and river shrimp, they can be reasonably easily weaned onto frozen foods, and this is essential for long term success.
Ctenolucius hujeta is the most common species in the trade. Although bigger in the wild, 20-30 cm seems typical in aquaria.
Cheers, Neale
Oh, for the Original Poster. [1]
Exodon are great fish for aquarists who want a "feeding frenzy" type aquarium but don't have the space for piranhas. At about 15 cm, tops, a school of a dozen specimens doesn't require a particularly big tank. In smaller groups they tend to be cannibalistic, so I wouldn't recommend keeping less than twelve.
Exodon eat anything, including pellets, but the fun comes from throwing in a frozen lancefish or whitebait and watching them go berserk. They absolutely do not need live food! [2]
Ctenolucius cannot possibly be kept with piranhas. [3] Black piranhas,
Serrasalmus rhombeus, are not sociable and not even all that active. Singletons can be kept in fairly small aquaria (~100 gallons) considering their size but they can't be mixed with anything. While they look nice, they're pretty boring, and are one of the more dangerous species in terms of biting the aquarist. Unless you're a very experienced and dedicated piranha-keeper, it's a species that probably won't appeal.
ok....and i thought that a frashwater barra. would work, or is it brackish?