Leopards suffer from the Mandarin problem (naturally pod eaters) and as such they are difficult to sustain in a captive environment.
As TJ also notes, I think this is outdated information. I've kept dozens of leopard wrasses over the years, and while the occasional individual refuses to eat, the vast majority that make it through shipping will take frozen far more readily than a mandarin will. When I have lost them post acclimation, it has either been due to aggression problems or weight loss even though they are eating (so likely internal parasites).