My molly is darting back and forth quickly in the front of my 20 gal...hes the only molly in there at the moment so its not a mating ritual ive ruled out...any idea what it is?
what are your water parameters, and what are its tankmates?
I had a molly be soo frightened by its tank mates one time (they weren't even aggressive fish) that she used to dart back and forth right before she jumped out to her death on my carpet.