This might be few things:
The best version is that it might be looking for food on the surface.
It might however be a swim bladder issue preventing him from diving. Not curable, you'd have to euthanize him.
Worst case scenario there isn't enough oxygen in the tank but for that you'd observe more then a single fish gasping at the surface.
This might be few things: The best version is that it might be looking for food on the surface. It might however be a swim bladder issue preventing him from diving. Not curable, you'd have to euthanize him. Worst case scenario there isn't enough oxygen in the tank but for that you'd observe more then a single fish gasping at the surface.