A general rule with digital cameras is that the regular camera companies (Nikon, Minolta, etc) usually build better digital cameras than the computer companies (Sony, HP, etc).
I also have a Nikon Coolpix 4500 ($615 from Pittman photo, back when they were in high demand). Excellent camera with lots of features. It received excellent reviews for macro shots (large close-ups of small objects), which is a desirable quality for taking pictures of your fish.
Of course, there are many more options out there. Do a net search and look for the many sites out there with detailed reviews of different digital cameras.
Cheers,