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 Sigma Photo 4.5mm circular fisheye 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.
A circular fisheye gets most all of what's in front of you and puts it into a circular image surrounded by a black field. If you've ever seen a convex mirror, the effect is very similar.
This Sigma Photo 4.5mm EX DC HSM circular fisheye features an f/2.8 aperture, so it's a good choice for indoor spaces.