Sargassumfish are among the most voracious of the anglers and will commonly eat fish larger than they are INCLUDING dwarf lions, unless you are lucky enough to obtain a really large dwarf lion and even then it could be risky as they grow to roughly the same size.
The Sargassumfish are also, IMO, the easiest of the anglers to get eating frozen feederfish (such as silversides), many eating them from tweezers or forceps the day you get them(always offer the feeders or pieces of feeders with the head and eyes, at least in the beginning, gently waving it a few inches in front of them).
DO NOT use feeder goldfish with these guys as it can have a negative to deadly effect on them in a very short time (mollies will work occassionally and actually live in the tank with them until eaten, eating algae until they become lunch)
Also Sagassumfish are among the most prone of the anglers to eat EACH OTHER, even including similarly sized fish.