Shrimpfish, in the same order as seahorses and pipefish. It’s thought they adopt this head down posture because they like to hide among sea urchin spines and vertical weeds; but they swim - horizontally, but vertically - pretty well that way too…

This was also at AOP; please forgive the weird reflections and slight blurriness. Last time I was there they had maybe three or four in a tiny tank of maybe two gallons, and now they have a school of them!  The tank is this sort of wedge-shaped thing with no air surface on the display side.

Note: there are also ribbon pipehorses near the bottom in this video.

Not sure what’s going on here - it plays on my dash and posts page but not on  my main page.  If you can’t see it let me know and I’ll put up a link.