You really need to provide a lot more information. To start with, what specifically are you shooting? Also, are you using flash? Even with this, exact settings are going to depend on a lot of circumstances we can't accurately predict unless we're right there with you taking the shot. If you don't already have a firm grasp on the relationship between aperture, ISO and shutter speed in relation to exposure as well as the relationship of aperture and focal length to depth of field, that's where you're going to want to start. From there, we can give you some good general guidance for aquarium photography.