Scatophagus tetracanthus, the African scat can live in fw. It also occurs in both sw and fw, and the only member of this species that can be kept in fw.
I think you are looking for the silver. If you look at the pictures I posted (sorry, not the best but it's all I've got) you can see that they are bright silver with black spots that form in a slightly striped pattern. If I ever get a large enough tank and have the time to eventually go salt with it then I will definitely have these guys again.
Scatophagus tetracanthus, the African scat can live in fw. It also occurs in both sw and fw, and the only member of this species that can be kept in fw.
All scats are born in freshwater and are commonly collected there and sold as freshwater fish. They eventually move out towards and into the ocean as they grow. Even the African scat is "supposed" to move into brackish and then saltwater. However, the African, like all of the other variations, is very hardy and is commonly kept in freshwater for life, as are greens, reds and silvers. As long as the tank is kept very clean this is not really a problem. What it does do is make them more susceptible to illness. For example, when I had my silvers I kept them in 1.005 brackish water. Before trading them in I spent a few weeks acclimating them back down to freshwater. The LFS I traded them into kept them in freshwater (I frequent the store and always dropped by to see them). The last two they have had for a while and they started developing a fungus on their dorsal fin. I went in the other day and the employees had moved them into the marine tanks so that they could live healthier and get rid of the fungus. The fungus was gone and their colors were brighter than ever. I asked about the acclimation and they said they just did a normal drip acclimation throughout a workday and then they put them right in.
In addition, they sell African scats out if the freshwater side and the marine side (both are $100 each) and the Africans that are kept in the marine side grow a lot faster and have much brighter colors.
I'm not saying it can't be done successfully, just that it's not technically the way they are supposed to be kept.