Compare Visual System of Fish to Human

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In fishes’ eyes the rods are physically retractable. When light levels are high the rods are retracted into the back of the retina and covered with a black melanin layer. When light levels fall and the cone sensitivity degrades the rods move upwards to lie alongside the cones to provide gray scale vision.

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The Reflective Eye

Some fishes have a Tapetum lucidum, a reflective eye, similar to nocturnal animals. They have a reflective system on the retina to reflect light which has already passed the rods, back for a second chance at detection. The sight is very slightly blurred but it is very sensitive.

The fact that these species have a reflective eye creates problems when fish are removed from photon limited water conditions and/or flashed with cameras. They can be heavily light shocked and become disoriented which does not help their survival on release in crocodile infested waterways.

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The Eye

Photoreceptor properties

Dynamic retina

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05-03

W. W. Norton

Human Photoreceptors

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Kusmic et al. (1992)

Retinal rods contain a visual pigment with max at 512 nm.

Adult trout the retinal cone system consists of single and double cones with pigments having peaks at

453 nm (single cones and one member of double cones),

530 nm (single cones and one member of double cones)

598 nm (one member of double cones)

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4 cpd

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‘High’ Frequencies

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‘Medium’ Frequencies

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‘Low’ Frequencies

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Species

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Wheeler, 1981

Teleosts

Animal's ability to perceive stimulus a function of temperature and season.

Specialized features

Reflective tapetum (part of pigmented layer of the eye, which has an iridescent luster and helps to make the eye visible in the dark)

Area and temperature dependent distribution of visual pigments

Area-specific distribution of photoreceptor types

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