Help with Collisions and movement

Hey guys, I was in need of some help with collision detection. I downloaded a ported version of the fish tutorial, and the first thing I couldnt figure out is how to make a fish dissapear when the player fish hit it. As well as having the player die when it hit certain things. The second thing I couldnt figure out is how to flip the image of the player when he turned left.

Thanks in advance,
Chris