Kalliff,
Not bad at all for a first timer. Just a few comments: the internal strobe on the 750UZ is not very powerfull u/w, if you can't reach out and touch your subject (2') you are too far away. External strobes (Ikelite, Inon etc) will give you a pinch more distance (3' max) before you start to loose your color, but closer is always better. For non strobe photography, use a UR-pro filter and then fine tune your color with the manual white balance controls. Your color should be great, but you may have to increase the ISO (light sensitivity) from auto or ISO 50 to ISO 100 or ISO 200 in order to get a not too slow shutter speed, as the filter absorbes 2 stops of light.
The other comments above from kdietz are important too. Try to shoot fish at eye level, not from above or below, and wait for them to turn 20-40 degrees inward towards the camera so that they are not alligned perpendicular to the camera. This gives them a 3d profile, hense more personality in their faces.
Good Luck,
Doug