Diamond Watchman Goby Not Eating And Emaciated

[Mr. Seahorse]

It's been a while since I have been on the forum, but a reefer I know has a Diamond Watchman Goby that is not really eating and very emaciated. He has had the goby for a year or more with no new additions. Any ideas what it is, or what can be done to treat it? The reefer describes the fish as "skeleton"

Thanks!