User blog comment:Jamintheinfinite/Subnautica Creature Evolution/@comment-26170033-20180410200906

I was under the assumption that hoopfish, bladderfish, and holefish were all related, not only because they look similar but because they all have a high amount of control over their body muscles to control movement, holefish by growing and shrinking their cavity, bladderfish by sucking and ejecting water, and the hoopfish by vibrating the hoop.

Actually they use the hoop to change water density around them. How.