I've hit a huge manta ray with my surfboard I flew off the board spectators at the beach said the manta breached the surface and flew for many yards. I felt bad for the manta but he was fine and kept swimming around the area for a couple of hours my board on the other hand tore out 2 fin boxes.
unfortunately with the foil I've hit a big turtle (he seemed ok) lots of jelly fish and even a big squid
never hit anything riding the Zeeko Spitfire because it whistles so loud I think the fish run away. I did manage to get the spitfire hung up on a fishing line with a midsize shark still attached on the other end not sure who was more freaked out on that encounter