Fish with a hole in his side

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On my yellow watchman goby, I noticed that he was having trouble growing a hole on his body near the halfway point. Not just any hole in the lil. I can see through him almost the whole way.

He's just looking odd to have a hole in him. To help him heal and be healthy, can I do anything? A week or two ago I noticed that the area was all white now that it has returned to the right color, leaving a good size hole in it.

I will try and get a photo soon. He hides that side from the tank front.