Things like this aren't that uncommon in nature. Look at how many conjoined twins we see in humans. If you look at it you'll notice the fish on the right is longer and thicker. This is the "dominant" part of the fish which does all the swimming and hunting.
The other will probably be rather weak and limp. It will more than likely hamper movement to a certain degree but, being an ambush predator it could catch fish quite easily still, irrelevant of its condition.
It's size suggests to me it is quite young, whether something like that could reach its 4 feet max size I don't know, probably not.