Look man I said that it can be kept in an 20 gallon but that was an example so people themselves can do the math themselves and yeah they shouldn't be kept in an 20 gallon . And looked up at some major websites and did a lot of research on these fish and I know that they should be kept in groups of 5 or more. And I can't say that Wikipedia is wrong I'm sorry, the growth rate is slow my friends. Go use the internet read it yourself. As far as the keeping two. I told him to keep three because at least the dominate one wouldn't kill the other one. And if he can't then he shouldn't keep them might as well get an oscarHi rajatariqmustafa15, sorry, but i fin dit a bit wrong when you write a info page on Piranha, but to ask advice on keeping them, then the next day you offer advice, and to offer advice that a RBP to be ok for life in a 20g tank. Please think first, not just read and repeat what you read, its not all good or true what you read on the net.