I have two of these, came with the tank when I needed an emergency replacement from Craigslist (Pacus...). They have lived successfully with an Oscar, Pacus and both large and small goldfish (not all in same tank). They are about 6-8 inches long, translucent to silver with purple spots on the side and light purple fins. They don't seem very aggressive and are quite skittish to light and movement around the tank. They swim high in the tank almost at the waterline and will preferentially swim across the tank at the same level rather than dive deeper. There is concealment at the bottom of the tank but they prefer to be in the open. Freshwater tank, about 75 degrees. They seem to like goldfish food, we tried them on everything (blood worms, live food, etc.) and they would not eat anything else. They have thrived for a year so seem to be "happy", just wondering what they are...can't find a comparison picture anywhere on the net. Any help appreciated. Thanks!!