Do you have any pellets or flakes for the fish (if any)? might try 1 or 2 to start. I had a nem that wouldn't take mysis after I received it, but had a good rate for a week with pellets. After that week, his/hers feedings where spot on with mysis, then to anything. Kinda like starting it into the normal procedure. Just keep an eye on it for any changes. The mouth is still closed so that is a good sign.