turn fish3d follow mouse

first sorry my english hello! there.

I have a problem with this.
I create a fish follow mouse (when you move the mouse the fish follow mouse cursor)
that is ok the fish smooth follow position.
The camera is in Z axis like a 2D game.
The problem of course is the rotation, i need the fish rotate smoothly the cursor.

when the cursor mouse is on the tail i need the fish turn around to his back.
I need the fish swing like a fish!!.
i need to control the turn around and how much is going to rotate when the fish follow cursor,
now the fish swiming with belly up when turn arround jajaa.
if some one remember (eco the dolphin) that is a very good example game. remember i am not using keyboard! like that game.
of course i need the fish turn left or right depend the position of the cursor.

i send a picture to explain

There’s some good reading here on following and evasion, hopefully you’ll find some of it useful.