False.
PDA description:
This unusual herbivore appears to be mostly defenseless, and bears little resemblance to the other lifeforms around it.
Semi-permeable Bladder: The bladderfish is able to filter air and seawater into its body cavity through a unique membrane which surrounds its spine like a bladder. This allows it to remove and consume organic particulate caught on the way, and adjust its buoyancy.
Open-ended Vascular Tubing: Can be angled and contracted to pump out water and achieve low-velocity, guided propulsion.
Largely oblivious to threats, and practically immobile at night, its only identified defense mechanism is that it's composed almost entirely of water, air and cartilage.
Assessment: Edible (oxygen may be retrieved from the bladder and added to tanks on consumption); membrane has applications as a natural water filter