Hello,
my camera set-up for aquaristic photography is:
a PENTAX K20D DSLR camera
with a PENTAX 18-55m II
I've used for the last pics the internal flash with less power (-0,5). The distance between me and the fish is normally ca. 30cm for portrait (with the use of zoom 55mm) or ca. 40cm for the whole fish (with zoom 30mm).
Now it goes a bit denglish (uh, where are the words?) ...
The shutter speed is 1/125 for portraits and 1/90 for the whole fish, the aperture (right word?) is 16-19 due to the situation.
The white balance i'm using is the flash modus, but i'm able to correct with the internal possibilities of the camera. So there's the function to set a white balance point to get the natural colours of the fish WITHOUT the effects done by the tank lightning (the lightning is preferred for aqua-plant-growing an do have a yellowish touch).
I disagree with the point of view of not-using a flash in aquaristic photography in the case of photographing bichirs. They don't like much lightning at all which is necessary for non-flash-aquaristic photography. You may keep the real aquaristic situation with all the colouring effects caused by the tank lightning but you won't get the sharpness when using flash. Non-flash is a good choice in non-planted cichlid tanks (plants + cichlids = salad) where the lightning reaches the fish without loss, but a bichir tank - or snakehead tank - is a completely different thing. The planting situation is an important reason why my bichirs and snakeheads aren't shy and growing fast (Lapradei +7cm in a half year, the Channa pulchra doubled his lenght in only 4 months ... and my new Polypterus ornatipinnis grew up 4cm in only two months ... and so on). A planted tank is also an eye-keeper and reduces cleaning procedures of the tank in a enormous way!
Uh, i forgot: I'm using ISO 200 with an extended dynamic range of 200% to avoid outshining of white parts of the fish.
I hope, i was able to help you a bit!
Greetings
Uwe