My favorite fish, "link" has been missing for about a week. Now I just got off of night float so I've been somewhat inattentive and I feared he jumped from the tank but today I looked at the tank for awhile for the first time and I noticed this odd cyst-formation on my frogspawn. Upon looking deeper at it I can see what looks like a skull floating inside of it. The fish was plump and happy before last week there's not a chance he died naturally. What do you guys think?