• Question: If humans can see water but not air, does that mean fish can see air but not water?

    Asked by ChristianMinecraft to Hugh, James, Katherine, Matt, Shannon on 9 Nov 2017.
    • Photo: Katherine Benson

      Katherine Benson answered on 9 Nov 2017:

      Our brains filter out obstacles to our vision and we developed so that our vision would filter out air. In the same way, fish don’t see water because their brains developed to filter it out of their vision.

    • Photo: Hugh J. Byrne

      Hugh J. Byrne answered on 11 Nov 2017:

      In fact, what we see depends on it having a colour, or a refractive index difference. Water has a different refractive index than air, and so it reflects a small amount of light at the surface (5%). Glass does the same. Most of the time, when you look through a window in the daytime, you don’t notice the reflection, but when it is dark outside, the reflection is much stronger than the light coming through (transmitted), and so you see your reflection. Therefore, in fact what we see is the boundary or interface between the air and water. the reflection is strongest when light goes from a material of low refractive index to high, so in fact fish wouldn’t see the interface very well. I don’t know, they may also be more sensitive to temperature differences at the surface?

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