Solitary, omnivorous serrasalmids around a foot?

[Hybridfish7]

Any ideas?

 

[tlindsey]

Any ideas?

Redbelly Piranha

 

[Backfromthedead]

Mylesinus paraschomburgkii. I dont see them available very often though.

 

[Deadeye]

Another vote for a red belly (or any of the pygos short of piraya). They will do fine in their own and will readily eat plant matter as well as meat.
I’m pretty sure the serrasalmus piranhas are more carnivorous than their pygo cousins, but there’s plenty in the size range as well.