Furnish the tank sparsely with plastic rather than live plants. With a larger type gravel or marbles but with alot of places for it to hide in. In a community situation be sure that other fish are as large or larger than the piranha and that they are fed at separate ends of the tank.

It is illegal to keep piranhas in some states in the United States. It is feared that released or escaped fish could make a home in southern waterways, like those of Florida or Louisiana. In fact, piranhas do not make especially good pets. People who own them say that they are shy. But somehow a few piranhas still find their way into home aquariums. If you have a piranha, it is not a good idea to put your fingers in or near the water. The fish might mistake them for food and bite them. In general, though, piranhas in aquariums are not very aggressive unless they are crowded or underfed.

When the piranhas are ready to spawn male and female adults will be wearing different colors than they do during the rest of the year, because they will be ready to breed. The Orinoco red-bellied piranha, usually silver and red, turns black with glittering purple or gold flecks. The black piranha turns even darker. Many colorful piranhas are more colorful and beautiful than usual. The female piranhas spawn, or lay eggs, during the rainy season in the wild. Piranhas probably court each other, like their relatives the tetras do. Tetra males and females go through a set of paired movements, as though they were dancing together, before they spawn. It is likely that piranhas do something similar. Right now, scientists know very little about how wild piranhas breed. They are probably sexually mature, or old enough to reproduce, when they are about a year old.