The Red Belly Pacu fish looks very similar and is sometimes sold to customers as the Red Belly Piranha. However, Red Belly Pacu only look like piranha as juveniles.
The red belly pacu will grow rather quickly and may reach 12 - 24 inches (30 - 61 cm) if properly taken care of. Given their potential adult size you will need an enormous tank to keep one at home, at least 250 gallons (940 liters). You will also need an extremely efficient aquarium filter to filter the tank water.