His iso was set at 800 for all of them. One can download and install an EXIF info viewer to see the settings used on many photos (unless image processing software has opted to strip the information).
NP_Reef, you're off to a good start.
+1 for using a faster shutterspeed. It is very difficult to hand hold at 1/20" and still get sharp pictures, especially if the subject can move, like a fish.
For fish, you could open up a couple stops (lower f number) or use additional lighting to be able to use a faster shutterspeed without making the pic darker.
For stationary corals, you can put the camera on a tripod and use shutterspeed of up to a couple seconds if need be. Use a remote trigger release or self timer to avoid vibration of the camera when activating the shutter.
Avoid center composition.