Lecture 27- vision

Question 1

the depth of water that includes light is called what?

Answer 1

photic zone

Question 2

how do fish deal with the refractive interface issue?

Answer 2

because the refratice index of the fish cornea is nearly equl to water the cornea is flat and does little focusing.

Question 3

describe/define snells window:

Answer 3

when a fish looks up its view of the terrestiral world is limited to a 97.6 cone. the whole surface hemisophere is compressed into the window. therefore often thinks fisherman is sitting closer than he is

Question 4

define extra-optic photorecepors:

Answer 4

photoreceptors other than the eye. as in many vertebrates fishes have a parietal eye on the top of their head that directly connects to the pineal organ within the brain. the information gained from this eye is used in determining seasonal timing, sun compass orientation and can trigger hormonal release initiation breeding/sleep

Question 5

the general anatomy and physiology of fish eyes is similar to other vertebrates with a few differences such as….

Answer 5

1. fish cannot change the shape of their lens. instead they move it back and forth to focus and judge distance.
2. fish do not have eyelids but some have nictitating membrane to block light and protect the eye
3. in most fish, eye placement creates a wide field of view but limited binocular vision.

Question 6

the sensitivity of fish to light, i.e the number of rods present is linked to what?

Answer 6

their niche. ith with lower abailable light need more rods than an open ocean living fish. hwoever, for fish living below the photic zone the production of rods becomes futile

Question 7

adaptations to low light:

Answer 7

1. pupilary response- have an iris that cannot move. hwoever a few teleosts and all chondricthyes have a pupillary operculum that is able to move in changing light.
2. retinomotor response- most fish have moveavle rods and cones. in bright light, cones are pulled fowards into the light and the rods extend back and vice versa.
3. tapetum lucidum: many crepuscular and nocturnal species like the walleye have reflective layers behind the retina that increase the sensitivity to low light. the tepetum licidum essentially recycles light and allows it to pass by the cones and rods twice.
4. blindness; usually found in fish lviing in caves like the mexican blind cave fish.
5. do it yourself- many deep sea creatures produce their own light using a chemical interaction similar to a glowsitck.