Yes, he is pretty thin. You can see his skeletal structure. Have you noticed what his fecal matter looks like. If you notice long, white, stringy waste; he may be infected with an internal parasite. Often, these fish stress when shipped, and being in packed import/export facilities, is an easy way to pick up an internal parasite. Since exporters purge fish (do not feed for 24-48 hours) before shipping, it's not uncommon for them to ingest their fellow fish's waste. When infected with an internal parasite, fish shed their intestinal lining on a regular basis, which is the white, stringy stuff we see. I would contact Reef Frenzy foods. They have a great mixture with probiotics, which he is likely to accept. Getting some probiotics into his gastro tract, wouldn't be a bad idea.