www.piranha-fury.com
piranha, depending upon the species, are mostly shy, reclusive fish that do not live up to the man-eating stories people often tell.
they are very cool fish in their own right, but you really have to find other ways to enjoy their natural behavior rather than thinking that they will "really tear up some feeders".
larger tanks, usually 55 gallon or larger.....but to do them real justice a 100 or larger is needed for the schoolers - nattereri, etc.
BTW- it is absolutley NOT necessary to feed them live foods, as they tend to be too risky with disease introduction and/or shear messiness (mouse idea).....many people find a local fish market and use sides of halibut, trout, and most other white fish to feed their piranha, which usually quickly adapt to such feedings. whole, uncooked shrimp are also excellent.
frequent partial water changes are worth their weight in gold
M