Breck, nice pics. I agree that David's pics are always a nice treat. I may be wrong but a lot of the time he is using a much nicer camera than a point and shoot. Maybe a DSLR or something.
As for your pics here, the second pic (the rainbow) is pretty good. There is a slight glare that you can only eliminate a couple of ways. You could try to take the pic out of direct sunlight so the all of the light isn't reflected off the fish and/or by not using a flash for the same reason. I am using an older Olympus tough series point and shoot. When I take fish pics, I shoot in Macro mode, and no flash. Of course this greatly slows the shutter speed and requires a VERY steady hand to avoid blurriness. It just takes practice. If I want to get a close-up of a particular part of the fish, say a brook trout's spots, etc., I use the super macro mode.
As for your last pic, it seems the exposure is off. I tend to do very little post processing to my pics. I might change the exposure slightly, as well as the contrast and highlights. Usually I don't need to play with saturation much. I guess there are lots of programs to do this, but I use iPhoto on my mac or occasionally picmonkey.com. Picmonkey gives you a ton more options and is almost like a free version of photoshop (but much more limited obviously). Maybe some of the real photographers can help you more, but I figured one amateur to another, I might be able to help a little.