tank mates for a 20 or 40 gallon

[viboy]

My 15 year old son is thinking about starting up his own tank.

He is favouring piranhas but I told him that they are not really a very aggressive fish.

I am looking for suggestions on fish for a 20 or 40 gallon tank. He is wanting super aggressive fish but I do not want anything that will need anything larger than a 45 gallons.

Any suggestions? I am not looking for just one type of fish. Suggestions on tankmates are welcome.

Thanks,

Dwayne

[SomeGuy88]

You could try convict cichlids, they are very scrappy especially during breeding time. A pair of them would fit nicely in a 20 gallon. You might like these guys here:http://www.aquariacentral.com/forums/showthread.php?t=32373&highlight=piranha