They're fish. Other residents have created other species of sea life, of course, and land animals too. But at best, they're impressive sculptures of animal life*, and when they move (if they do at all), it's only along a pre-scripted flight path, like old school animatronic sea beasts from Disney's underwater sub ride. (It's not uncommon to glance out from the shore of a Second Life beach, and see a pod of dolphins endlessly leaping out of the water, stuck in an infinite Flipper loop.)Link (Thanks, James!)
Surina's fish, by contrast, flow together in a school that changes shape and direction, dispersing sometimes, then gradually regrouping; occasionally, maverick Nemos will trail off from the school to go on their own adventures, only to eventually return, chastened, into the fold. When a Resident joins them under the sea, the fish wander over to them, and mill about; it's not unlike wading into Hanauma Bay nature park, and watching as partially tame schools of fish come over to you, curious. ("I added the instinct to shoal around avatars," Surina explains, "which is why the fish are staying with us and not swimming off.")
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.