Who said swimming was easy?
And who’d have thought that large pufferfishes like this one I photographed 20 years ago were amongst the steadiest swimmers in the sea? Until I read a 2001 research article (accessible pdf here), I had thought quite the opposite.
It notes the six different ways a fish can end up recoiling when it tries to move: surging back and forth, heaving up and down, slipping side to side, yawing round and round, pitching head over tail, and rolling like a corkscrew. Most swimming gaits require their users to make significant compromises on some of these recoils in order to make any progress at all.
But (although the article focuses on boxfishes, which are related to puffers), it shows just how few compromises are needed when using their apparently bizarre fin arrangement in what is called the tetraodontiform gait.
A more recent article (accessible pdf here) even posits that some puffers literally puff water asymmetrically sideways out of their gill covers to act like fine trim controls to counter minute yaw variations. Wild.