There is a sticky labeled "How to take a good photo" at the top of this forum page with some good info. It's long, but a good read.
Basically, it's more a matter of getting used to the camera. You will definately find that the manual settings work much better than the automatic ones. How you set it up will depend heavily on what you have, both in the camera and in the accompanying equipment (tripod, lights, etc.).
After reading the sticky, try different things with the camera. You may have to improvise if you don't have the same stuff other people have, but that's part of the fun.
If you aren't used to making the manual adjustments, write down your camera settings along with the photo number the camera assigns and snap a picture, then make a change (again, writing down your settings) and take another shot. Do a series changing only one of the settings (aperture, exposure, etc.) until you can identify what is happening, then start another series changing one of the other settings. It's a great way to learn about your camera, plus gives you the experience so you don't end up just pointing and shooting on the automatic settings. You will find more satisfaction with these types of pictures.
When you finish a series, compare the pictures and see what works best for your needs. For me, putting the pictures up on the computer screen is better than relying on the LCD panel on the camera because I can see the details better. This way, you can see exactly how the changes you make to the camera affect the picture you are taking. (Admittedly, this works better with something that doesn't move and a tripod for the camera so it stays still, but hey, we are combining two hobbies here.)
It just takes time, patience, practice, and a lot of cooperation from the fish...
Good Luck and enjoy!