My shubunkin seems isolated from the other fish.  He doesn't seem to be eating. He can swim and looks healthy but I noticed he seems to be making a lot of bubbles on the top of the water and around the edges of the tank.

Is this a sign of lack of oxygen or is it something else.  I have cleaned the tank and I have a filter. So what could this be?  I have had this fish for six months and there doesnt seem to be any bullying by the other fish , this one is just lethargic. There are five other very small goldlfish in the tank with this fish. All healthy.

OTS

Sounds like lack of oxygen due to overcrowding.
How big is the tank?
Water test results?
As Hanna said you reallyshould copy and paste the questions in the health issue sticky and post the answers here.  We need more info to hep you better.
Also, besides a filter do you also have an air pump witrh airstone of some kind going in the tank.
We need to know how big the filter is and what kind.
Thanx!

Oh That is sad but now action must be taken anyway. Why did this fish get sick? Can you fix the cause of the problem/death? As you now have plenty of other fish at risk!

No offence but you sound like a newbie to this as we were all once  Could you please give us more information on your tank, your fish, your tank maintenance, what you feed them, your filter, etc. This fish probably could have survived though it's not your fault but I'm sure you don't want your others to die.