ooh, pretty! I didn't realize they had freckles. I like fish with freckles :-)
I noticed that you were shooting at 1/60s. Ya, for fast swimming fish you need to shoot a bit faster (shutter). This means a larger aperture or higher ISO (usually both!). If you are maxed out on all 3 settings then there isn't much you can do other than upgrading equipment (lens or body). For the faster fish I gave up on trying to chase them with the camera. Instead, plant yourself in one spot and wait for the fish to swim by. Often when you're chasing them you end up tilting the lens and shooting at an angle which will introduce distortion. A tripod isn't going to help with the fast swimming fish because you really need a fast shutter and at that high a shutter speed camera shake from your hands won't be registered.
My last suggestion is to ask a friend (perhaps one that works with you), to drop by with some expensive equipment and photograph your entire tank for you.
