So... after long deliberation I decided to hold off on the macro lens, so I picked up a set of macro extension tubes... I am IMPRESSED! They work really well, and the shot below was made with them. I used my 85mm 1.8G lens with a 20mm lens, and had full autofocus capability. I lit the shot using 3 off camera flashes-- two on top, and one in an umbrella on the left. I also added a flag to the left front edge of the aquarium to limit any reflections off the glass. See below for a "how it was shot" photo.
Black Phantom Tetra by f_one_eight, on Flickr
How it was lit:
Cheers!
Jake
Black Phantom Tetra by f_one_eight, on Flickr
How it was lit:
Cheers!
Jake