Eibriel on Nostr: I would suggest you to not use any kind of physics simulation for that, and instead ...

I would suggest you to not use any kind of physics simulation for that, and instead research "Boids" . Think about the fish as a point, and set the rotation according to the direction of movement.

If you still want to use physics you can try using a CharacterBody3D node for the fish and setting gravity at 0 for it. That node keeps the rotation.