Field-of-view:

The bodies of freshwater panfish like bluegill are narrow and the eyes are set far out on either side of the head. This gives them incredibly wide field-of-view approaching 360 degrees in all direction but directly beneath and behind the animal. In order to see in all directions, fish sacrifice binocular vision which only overlaps in about 20 degrees of vision.

Interestingly, the field-of-view of the above-water world is compounded by the physics of light refracting through the water’s surface. As oblique light hits the water’s surface, it is refracted to a more acute angle. In essence, this compresses the field-of-view, acting like a wide-angle lens for fish. That explains why it is so hard to sneak up on fish along the shore!

Image: Figure demonstrating the refraction angle of light at the water's surface as seen by fish; by Richard Fitzpatrick, University of Texas.< \span>

Depth-of-field:

Since the refraction between water and the cornea is minimal, accomodation is easy for fish, granting them a very broad depth-of-field underwater. The human eye has not evolved to accomodate the minimal refractive differences between our cornea and water. Thus, we humans have very poor eyesight underwater (unless, of course, we use goggles that sandwich a layer of air between the water and our corneas). 

Focal field:

Most teleost fish do not possess a fovea. Visual acuity is constant over the vision field. Teleost fish eyes never stop growing. In order to retain vision without impairment as the retina expands, new rods are developed between existing retinal cells (Fernald, 1990; Joselevitch and Kamermans, 2009). Since this maintains a constant rod density while increasing the visual plane, fish sight actually improves with age!

Spectral sensitivity:

Most teleost fish are tetrachromats able to perceive color in the human visible range and UV; however, bluegill possess only two cone-types (Hawryshyn et al., 1988). This allows them the best color vision in red and green frequencies, but no discrimination in the blue range.