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Fish Vision

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Compare Visual System of Fish
to Human
By Dan, Derrick, Juveria, Tim
Fish: The Evolutionary Solution
• "Fishes are the evolutionary solution to a number of
mechanical, aural, optical, structural, electrical and other
engineering problems relating to the environment in which
they exist. They are complex organisms, or animals, and
their sensory systems have evolved to provide the
necessary functions to make the whole fish a viable entity
in the watery environment"
Color Blind
• Humans, who are only one species, and who can see all of
the colors of the spectrum have a trichromatic visual
system. They have blue, green and yellow/orange sensitive
cones in their eyes.
• The fish may be trichromatic, and have three color
pigments The retina of these fishes will have the cones
arranged in a matrix. This might be a blue sensitive cone
surrounded by green and orange/yellow sensitive cones.
• The fish may be dichromatic (deep water species) and have
two color pigments. The retina of such fish might be made
up of only two color sensitive cones, blue and green; in
which case it will be a blue sensitive cone surrounded by
green sensitive cones.
Beyond the Visible Spectrum
• Color vision is our visual systems
sensitivity to light photons in the band of
electromagnetic frequencies called the
visible spectrum. It goes from red, orange,
yellow, green, blue, indigo to violet. We do
not see infrared or ultra violet but some of
the fishes may see infrared and one species
at least, the blue, or slimy, mackerel, does
see ultra violet.
Some Similarities
• We and the fishes have an adaptive eye that is
sensitive to the illumination level. If the light level
is low or photon limited, there is no color vision.
The brightness of the color or brilliance depends
on the illumination. If the illumination is high the
color is light and bright. If it is low the color is
• We and the fishes need at least two color sensors
before the brain can discriminate color hue or
Gray Scale Vision
• The rods are for gray scale vision and merely count photons regardless
of color.
• In Humans the retina contains both rods and cones. Each rod has a
drop of Visual Purple, or Rhodopsin, on the tip. In bright illumination
this bleaches de-sensitizing the rod and protecting it from the bright
light. As the illumination degrades the visual purple is re-generated by
vitamin A and allows the rod to detect very low-level light photons.
The lack of vitamin A in the body can lead to "night blindness" or a
low level of gray scale vision.
• 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.
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
The Eye
• Photoreceptor properties
• Dynamic retina
Human Photoreceptors
W. W. Norton
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)
4 cpd
�High’ Frequencies
�Medium’ Frequencies
�Low’ Frequencies
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
• Area and temperature dependent distribution of visual
• Area-specific distribution of photoreceptor types
Wheeler (1981)
• Cyprinid (soft-finned mainly freshwater fish
typically having toothless jaws)
– At least 7 distinct photoreceptor types.
– The receptors are not only the first neural retinal element,
but also act as interneurons and display the first indication
of antagonistic spectral and spatial response properties.
– Produce the high spectral and spatial resolution at the
ganglion cell level.
– Bipolar cells form direct contacts with receptors and
ganglion cells. The bipolar cells therefore provide a direct
straight-through information transfer pathway.
Saszik, Bilotta (1998)
• Like other fish, the dark-adapted visual system of
the zebrafish can be influenced by water
– Warm (28–30°C)
• Spectral sensitivity consistent with the rhodopsin absorption
– Cold (22–25°C)
• Spectral sensitivity function that was the result of a
rhodopsin/porphyropsin mixture
– In addition, ultraviolet cones (362nm) contributed to
the dark-adapted spectral sensitivity function under
both temperature conditions.
Powers, Bassi, Rone, Raymond (1987)
• New rods are continually generated and
inserted across the entire differentiated
retina in juvenile and adult goldfish
– No other retinal cells share this characteristic
Mikolosi, Andrew (1999)
• Cerebral lateralization is revealed in the zebrafish
by preferential eye use.
– differs according to the visual stimulus that is being
• Right eye is used when the stimulus (or scene) is
such as to require a careful period of examination
in order to decide on a response.
• Left eye is used when the fish has to check
whether an identical stimulus has been seen
The Double Cone
• The double cone is a cone with a secondary
cone wrapped about it.
• Birds, reptiles, fish, and amphibians all have
double cones.
• Scientists hypothesize that double cones
allow certain color processing functions to
happen at the cone instead of at the
The Double Cone
The Cone Mosaic
• Cones in fish are arranged in a pattern in the
retina known as the cone mosaic.
• Two types of mosaics exist: Square and
• Patterns are dependent on the species of
• No purpose for the mosaic has been found
The Cone Mosaic
Zebrafish (Row Mosaic)
Medaka (Square Mosaic)
The Cone Mosaic
Two major types of visual
• Rhodopsins
• Porphyropsins
Three other types that appear in some fish:
Kynurenine (3-hydroxykynurenine) (370nm)
Carotenoids (425-480nm)
Mycosporine-like amino acid (300-360nm)
• Some fish, including the Japanese dace fish, carp and the
common goldfish can see UV light.
Visual System of Billfish
• Vision concentrated in forward and
backward directions
• Able to resolve 10cm object at 50m (typical
for fish)
• Billfish has larger than average eyes which
don't improve visual acuity, but are better
able to see while moving at high speeds
• Adaptation for predator
Visual System of Billfish
• Color photoreceptors concentrated in part of
eye that faces up
• Part of eye that faces down contains
photoreceptors sensitive to light
• Adaptation for clear-water environment
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