What kind of P?

  • We are currently upgrading MFK. thanks! -neo
that's s. maculatus... they are one of my favorites, i have a couple myself. a 75 gallon would be a huge tank for a small mac, but if you don't mind having one smaller fish in there, i'm sure it'd be happy as hell.
 
a mac cohab is a pretty big thing to undertake, i wouldn't recommend it unless you have alot of experience and you are able to keep a very close eye on them and have tanks to move them into if/when you end up needing to separate them. if you want more than one fish in the tank, a few natts or caribes will be your best bet.
 
Serrasalmus sanchezi
Serrasalmus-sanchezi.jpg

Small Piranha but doesn't have a solid common name or much of a taxonomy. However they are popular in pet trade as Red Diamond Piranha or Ruby Spilo.
Picture/Info courtesy of wwww.thejump.net
 
MonsterFishKeepers.com