Tips on Shooting Fish?

A friend asked me to take some pictures of his fish in a tank. Anything I should know to make it successful, like maybe manual focus or metering? Thanks for your help.

Put them in a barrel : )

(I'm sorry, I couldn't resist)

Dirty glass and reflections are going to be the biggest problem. Clean the glass twice and dry it off well. Then there are reflections. The bigger ones can be avoided by not shooting straight-on but at an angle. If you have one, a circular polarizer may be worth experimenting with. As far as metering, my guess would be to start out with spot and go from there.

I think a rather narrow depth of field would be best, really blur out the background if possible. This will also let more light in and allow you to get your shutter speed up. Highish ISO is going to be desirable, too. I'm guessing a flash won't work out too well, but maybe with a diffuser, it may. Sounds like there's a few things to mess with here.

Do look forward to the pics, hope you post them!

Thanks for the tips. I do need to get another lens as I don't think my 300 will do too well