I've had my Diamond Goby (Spot) for 6 months or so and he has always been very active and a big eater. He has also always kept my sand bed pristine with his sifting, but about a week ago I noticed a bit of diatom buildup in the one corner of the tank that get very low flow. I figured Spot woudl get to it eventually and did not worry but it started spreading a bit more over the next two days. A couple of days ago I was watching the fish eat and realized that whiel spot was chasing after food he was not actually eating any of it, keeping his mouth closed and basically ramming through the food. Curious I dropped some small sinking pellets in and sure enough he just kept head butting the pellets without opening his mouth. I have been watching him closely for the last few days and it appears he is completely unable to open his mouth, it is not even moving a little bit. Even if his jaw was hurt I would have expected to see at least a little movement but it is like it is glued shut. Has anyone else witnessed something like this and have any advice? There is no sign of damage to the mouth that I can see, and he comes straight to the glass when he sees me so I have had plenty of time to examine him.