heres one......
glad you know what ya doing with it....mind you these guys are hard to catch anyway! but most of my picture of fish seem to come out like this one....
The problem with your image is noise from a high ISO, some camera shake (and fish more blurred due to movement) and fish is under exposed.
You can try a higher ISO which will increase shutter speed (and this is very low btw if you apply the crop factor rule you need at least 1/33" to get a reasonable steady shot. Not sure how antishake works with your camera I think it bumps ISO - was this enabled?
Basically you have got to increase ISO (at the expense of more noise) or use a flash, as all the above is because there is not enough light coming from the tank!
First, try a flash shot, angled so you don't get the reflection of flash in the glass - see if this helps.
Then, try a non flash shot but make sure anti-shake is on if it wasn't before, and increase ISO to 3200 or whatever the maximum is and see what the shots look like then.
Fish may still be slightly underexposed because camera has metered for whole tank and fish, being a small part of the picture is quite dark - upping EV will sort this out but again at the expense of blown highlights haha (see above as this is perfect example) i.e. the bleached effect of the pebble will be larger and more pronounced AND slower shutter speed which means more likely to get camera shake!
First and foremost, I think it is too easy to expect miracles out of cameras these days, but photography is still an art and takes a long time to get real good results. Don't worry and learn how your camera operates to get the best out of it!
So lets see some more practice shots
Exposure 1/9"
F number 2.8
ISO 800
Focal Length 5.9mm