Okay, the Fish/Fineas dialogues we've been seeing are taking place inside their shared skull. I get that. So Jon and Diablo and the rest have only seen Fish go from sweet to mean and back, possibly with a brief spell of glowing eyes.
So, let's see if I've got this right: Fineas has used the turtle/doomsday weapon to split himself and Fish into two separate entities, plus one more that apparently didn't get the immortality upgrade the others have.
Right?
How many "Fish" are Jon and Diablo seeing now? Two live (one with goggles he didn't have a second ago) and one dead? One live one with goggles and one dead one without? Just one live one with goggles (in which case their problems just got bigger)?

Crap, no EDIT function.
I just took another look at the strip and Jon is definitely reacting to the sudden appearance of two new Fish. Diablo also seems to be looking between Fish and Fineas at the dead Fish.

Still, that's a hell of a cliffhanger there. At least we don't have to wait until April 23 to see what happens next.

It is pretty established that fish has two persons in one body: fish and fineas. Where I'm treating 'person' as 'independantly thinking entities.'

It seems reasonable that since they are persons, a device such as the turtle can be used as a personal transporter can be used to transport them anywhere. (Since it can most likely transport anything anywhere)

Fineas, controlling the fish body, used the turtle to teleport the fish person and the finease person out of the fish body and into the pub stub.

It would then seem that the fish body, not without any soul/personality/essence/KFC buckets, croaked as a result of not having anything in it that is capable of living.

I agree insofar as Fineas has clearly used the device in its Personal Transporter capacity to transport both himself and Fish a few inches over.

However, the device clearly works by generating what is essentially a clone in the new location and killing the old one - it is, effectively, a smaller, turtle-based version of Tesla's machine from The Prestige. (Don't tell me I was the only one thinking it!)

That is, the dying fish portrayed is indeed the Fish/Fineas hybrid we've been following up to now, and the two living fishes are newly-generated versions.

Insert jokes about suicide, DID and hostage situations here.

The only things I will add are that a) the third fish is obviously choking, so this is perhaps the "original" real fish that got sublimated after all those years of living in beer
2) Jon has already established that all teleportation requires the destruction of the original and the creation of a new clone at a new location, at least in a metaphysical sense if not in a strictly quantum mechanical sense. That is, it's a matter of applying quantum information to a new set of particles, not a matter of updating the location information on the original set of quantum particles.

This is pretty accurate.