exploding fish?

Question
Hi. In the last week we have had 2 fish in our 90-gallon tank...explode?  One female silver mollie and one unknown gender iridescent shark.  Both bloated up and died in a matter of hours.  The mollie appeared to leak a string of slime from one gill, and the shark did so from its "bum" (?)  The mollie took less than 2 hours to die, the shark about 4.  The other fish are healthy, no sign of any problems.  Water is 7.5 pH, no ammonia or anything else, 77 degrees.  Any ideas?

Answer
Hi Sarah,

The Iridescent Shark death is sort-of a blessing in disguise. Sounds callous, but they are one of the biggest catfish in the World. Check them online, they aren't exactly cute.

I think I know what this, I'm taking a guess but the only parasite I know in this trade that actually explodes is a nasty bugger called Myxobolus sp. Where there any rice-shape looking cysts on the fish when they died?

You may well be about to battle to something I've never seen beaten.

Tom