All this mod does is make vanilla fish attempt to swim away from projectiles, dropped items, and primed tnt.

Why does this mod exist?

This mod is a joke about some of the advertising/behind the scenes of Call of Duty: Ghosts, where one of the points made about their new innovations is "Next generation Fish AI".

Their selling point was having fish swimming away from players (and maybe projectiles) to make them seem more dynamic and responsive. In practice, it works.. but isn't very reliable or breathtaking. Definitely overhyped.

So onto minecraft. In the base game, fish will already swim away from nearby players. This mod makes them attempt to swim away from dropped items, primed tnt, and projectiles as well.

Modpacks: sure. Not quite sure why you'd want to, but go right ahead!