fish in flash

So the idea we have is that we will have a shark that moves around at random, coming it at random points and takes a random amour of time to come into the stage.
We want this to also happen with our other fish but we want them to avoid the shark as it comes near them swimming in an opposite direction swimming into the distance or something along those lines.
We would also like the smaller fish to be able to interact with the scenery and back ground, the way we have thought about getting around this is to add a layer above the back ground which when the fish swim to hide
their animation sill stop behind the raised scenery hiding the fish, and making it allot simpler for us, this could also tie into the idea we have for the fish to react with the shark  and other things.
and finally we would like to add the ability to click near fish and they would respond , but something like a shark might just swim slower and not turn around and swim away.

this is what we would like to be in our finishing flash animation but at this stage its starting to look like we might not make it because we are falling behind some what.