Most people have a misconception that the more piranhas in the tank the more aggressive they will be, this is not true, infact keeping too many piranha together only contributes to their skittishness. They do not fully trust one another, and being cramped in close quarters with each other only makes them more skittish and causes them to dart all around the tank, its what I call a "Paranioa chain-reaction." One piranha may swim to close too another and the piranha will be afraid of being nipped by the other, then darts away scaring another piranha causing a chain-reaction of the whole school to bash their heads into the tank walls trying to get away. This also leads to the misconception of piranhas being very skittish, they are just shy fish. I keep 2 red belly juveniles, that live in a 60gallon tank, they are not skittish at all, because they have alot of room between each other. The only time they get scared and hide is when I have my hands in the tank.

In general most piranhas are shy and not that aggressive, so do not buy any piranhas if you think they are vicous aggressive fish that can kill anything, because they are not. There are exepctions however, such as the Black Piranha (Serrasalmus Niger), White Piranha (Serrasalmus Rhombeus) Black Diamond Piranha (Serrasalmus Spilopleura) etc. I would NOT recommend these species to any beggining piranha keeper.

When you first buy your piranha and put them in their new tank, they may act very wild and bash into the tank, or even play dead, dont worry, this is normal for newly bought piranhas. This only lasts untill they get used to their new surroundings.