Not a piranha, but close - it's a pacu. These are the piranhas' mainly veggie cousins. Colossoma macropomum (sp?), I think, although it's been a long time since I was a professional fish-keeper-bloke. 
Is the first fish one of those Spanish barbel jobbies?
Anyway, that's my first post over with. Shame I had to edit it twice! Cue barracking from Trogg. [:I]