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.