Green and Gold Sevrums are considered to be one of the more "docile" members of the South American Cichlid family. They grow approximately 14"-16" and come in two color varities, the natural green, or a pinkish-white called gold (not true albinoism).
Usually they can be bought at about dime to quarter size for $2-$4. A palm size is gonna cost at least $5. They're not overly aggressive, but can defend and hold their own against many of those fish described as "semi" aggressive. They should be the same size or slightly larger than tankmates to prevent them from getting overly picked on.
I've kept Severums with Firemouths, Silver Dollars, Tinfoil Barbs, Bala Sharks, African Knifefish, Blood Parrots, Convicts, Plecos, Clown Knifefish, Gouramis, baby Jack Demsies, baby Oscars, and a small school of seven Tiger Barbs.
Be wary though, if a Sevrum could catch it and fit it in it's mouth, it will eat it. The lab I once worked for kept a full grown (must've been at least 18"
Gold Sevrum in the sump of the fathead minnow grow out unit as predator control to keep the minnow population down in the sump. They never fed the Sevrum, it just ate the fry that got into the sump.
~~Colesea