I agree, optical zoom is going to be your friend with fish pics. That camera that Dylan (Flamingo) suggested would be a good one. 10x optical zoom.
And looks to be in your budget....I'd jump on that one.
Some people think megapixels are what you are looking for, but thats not true for fish pics...you want the best zoom you can get for the money. And if it has a macro mode, thats even better.