Wait a second here, apparently in the Ai_shark datablock I put canride and rideable twice, well that was dumb of me.
I don't know why it's not working now.
Edit: wait now I think I know what's wrong, do you have ParasiteZombie::onadd in your script?
If not that's why it's not acting like a zombie, copy it from ai shark, or any of the other zombies and rename it appropriately.