I am assuming Pygocentrus Class, right......The Serra family is a lot more complicated in breeding due to the fact they are more of a loner piranha as compatred to the red belly, cariba, ternetzi, types.........I have bred red belly piranha many times over........Breeding size starts at 5 inches........Usually the females have a lot more egg-shaped, round belly....The males are thinner and more pointy.........Breeding pairs darken to almost pitch black just before spawning.........They will clear an area by blowing the gravel out the way, making a "nest"........After eggs are layed, the pair will gaurd untill hatching.........Personally, I siphon the fry out right after hatching and place them in a 100g growout.....The growout is empty of any decoration and is simple........Temperature maintained at 78 degrees........The water level is half way....I do 50% water changes evreyday for one month........As soon as the fry soak up their egg yolks, I feed them baby brine shrimp(BBS).......BBS gets them growing really quick.......My fry reach dime size within 5 weeks..........At this time, I toss in shredded/bashed shrimp, crushed pellet and flake........All the time feeding BBS as the staple everday, the fry grow fast.........