It does look as if he has an infection and will need some treatment by a vet.

Can you do a clear, unflavored pedialyte soak? It's 1 part pedialyte to 10 parts dechlorinated water. Soak for 15 minutes. This will give him some electrolytes.

How is his home set up?

When did you first start noticing symptoms?

When did he stop eating?

If you can answer the trouble in the enclosure questions it would be very helpful for us.