Paul,
to be honest I am not the one to critic photos, since your pictures are far better than anything that I have ever produced.
But since you asked for it, there is something I see in your pictures I do allso se in some of my pictures:
The object is very often in the center of the picture. That doesn´t look as pleasing as if it would be placed slightly off the center. One good example is:
http://www.3at5.com/photoalbums/200408buna...ll/crw_1919.htm
This is slightly off center and looks perfect.
This one: http://www.3at5.com/photoalbums/200408buna...ll/crw_2130.htm is placed in the center and doesn´t look as good.
Sometimes you seem to focus on the eye of the fish, which is OK, but not with the middle focal point, you could use the left, or the right focal point instead.
Examples:
http://www.3at5.com/photoalbums/200408buna...ll/crw_2048.htm
http://www.3at5.com/photoalbums/200408buna...ll/crw_1916.htm
But those are just small critics. Congratulations on your work!!!