I have been told that to take photos of fish to get a camera with a good macro mode and a sports mode. The macro bit lets you take close ups of small things and the sports mode gives you clear shots even when the subject is moving....i.e. FISH fit both criteria.
For me I chose the Pentax Optio s50 or s5i. The only diff between them is the s50 runs on standard double A batteries and the s5i runs of rechargeable Li-ion batteries. They both have 5MP, 3x ooptical zoom....dunno about the digital zoom, super macro mode and sports mode.....can't remember the other features.