Cape sole

Heteromycteris capensis. I hope I have got the identifocation correct as there is another species of sole in this tank.

Correction
I now think this is actually a blackhand sole, (Solea turbynei). The black pectoral fin is not clear in this photo, but it is shown better in some other photos of the same fish; the lack of a clearly visible lateral line and the anal ray count confirm this.