In fact, the marine life in this game is why I decided to make this post.
The game features dozens of species of organisms swimming all over the place. As someone who has regularly struggled
creating 3D models of various animals, I can only respect the monumental achievements in modelling, texturing and animating so many fish (bony, cartilaginous, jawed and even jawless!), mammals, molluscs etc etc! All of these jetting around the place hunting each other and exploring.
Most big games do not dare populating their environments with this much life both due to computational demands and sheer artistic workload, but Abzû makes it look easy!
But the game is also aware of how incredible its environments are, as it has a meditation mode where the player character can rest while you can entertainingly and educationally zoom from critter to critter and study their models and movements. The only information given are their common names, and I appreciated that as I could search for information about them while enjoying the marine audioscape.