Hmmm mine occasionally closes if something brushes up against it (like me) I'm sure if some fish picked at it, it'd close up as well. Mine used to do that when I had a couple dwarf angels in the tank (i'm sure one was the culprit) since removing the fish though it pretty much stays with polyps out all the time.
It has been like the pic for a few weeks, then closed up for like a week and now it is opening up again. I am wondering if it is digesting food for the closed time and catching food during the open time. Believe me every time they close I cringe and hope for the best.
