Get the big picture
Who knows if fish really see the world the way a fisheye lens does. The good news for them if they do? They can see a lot of things coming for them. Fisheyes are known for extremely wide angles of view, and extreme distortion of space. Don't think this is a bad thing: when used in the right situation, fisheye lenses can lead you to new and unique perceptions of the nature of spaces around you. Try a lens like this on a city street, or a long subway escalator, or taking a close-up of your dog. You will no doubt find new and different ways to document the world around you.
This Sigma Photo EX DC 10mm fisheye features an f/2.8 aperture, a light-thirsty spec that points up this lens's ability to work in subdued and low light, so you'll find it a natural for interiors.