Ah. Thinking this is a fish is a common mistake many dealers make. In fact, it's a colonial tunicate. Notice the honeycomb pattern of intake siphons along the side; particularly fascinating is the one that structurally mimics the eye of the "fish". By means of controlled exhalation of water through the siphons the "fish" is able to "swim", albeit in a haphazard manner as it has to rely on it's notochord as a sort of rudder.
Checking my tunicate references, I'm going to tentatively label this one as Pyrosoma talkingoutofmyassia (Li Eng, 2003)
