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 dark. We and the fishes need at least two color sensors before the brain can discriminate color hue or difference.

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 waterways.

The Eye Photoreceptor properties Dynamic retina

05-03 W. W. Norton Human Photoreceptors

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

Species

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 D

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. D

Saszik, Bilotta (1998) Like other fish, the dark-adapted visual system of the zebrafish can be influenced by water temperature. –Warm (28–30°C) Spectral sensitivity consistent with the rhodopsin absorption curve –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. D

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 D

Mikolosi, Andrew (1999) Cerebral lateralization is revealed in the zebrafish by preferential eye use. –differs according to the visual stimulus that is being fixated 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 before. D

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 ganglion.

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 Row Patterns are dependent on the species of fish. No purpose for the mosaic has been found yet.

The Cone Mosaic Zebrafish (Row Mosaic)Medaka (Square Mosaic)

The Cone Mosaic

Two major types of visual pigments: Rhodopsins Porphyropsins Three other types that appear in some fish: Kynurenine (3-hydroxykynurenine) (370nm) Carotenoids ( nm) Mycosporine-like amino acid ( nm) Some fish, including the Japanese dace fish, carp and the common goldfish can see UV light.

Visual System of Billfish (marlin) 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 (marlin) 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

References as262/neuroanatomy.htmhttp://instruct1.cit.cornell.edu/courses/bionb424/students2004/m as262/neuroanatomy.htm as262/neuroanatomy.htmhttp://instruct1.cit.cornell.edu/courses/bionb424/students2004/m as262/neuroanatomy.htm as262/neuroanatomy.htmhttp://instruct1.cit.cornell.edu/courses/bionb424/students2004/m as262/neuroanatomy.htm