Fish Senses Vision Eye position w Lateral to

Fish Senses

Vision

Eye position w Lateral to forward w Allows vision to side as well as forward w Monocular to side, some degree of binocular to front

Top-Down View of Fish Eye Structure Fish perceive both visual fields independently.

Typical Fish Eye w Large, round lens (can’t change shape) - refracts light better underwater w Focused by moving lens anterior/posterior w Pupil/iris change little - low light environs - lens may actually move through iris

Four-eyed Fish w Each eye has two lenses w One for above-water vision, one for belowwater vision

Deep-sea Fishes w Eyes tend to be tubular to gather more light w Eyes also tend to be proportionally larger relative to head size

Colored Corneas w Colored corneas function as light filters w Absorb specific wavelengths of light w Yellow corneas absorb blue and green light w Increase contrast at low light levels

Rods in retina w Rods are physically retracted when light levels are high (cones are static) w Higher proportion of rods to cones than in humans w Rods can be retracted in some fish and covered with a black melanin tissue

Cones and Pigments w Cones distinguish between various colors (wavelengths) w Each cone has a pigment which absorbs light of a given wavelength w Different fish may have different pigment make-ups based on environment w Some fish have pigments that absorb at UVrange wavelengths

Fish and UV Light w Most teleost fish possess a type of cone which is sensitive to UV light (~360 nm) w UV vision may have been co-opted by evolution for other purposes (i. e. , mating) w Aquatic UV vision is most likely short-range

Perceiving Light is Difficult Underwater w Changing water conditions drastically affect a fish’s ability to see w Contrast is chief detector of objects such as other fish, plants w At different depths, color perception is very different

Sharks w Sharks have few retinal cones, relying mostly on rods for photoreception w Sharks are extremely sensitive to light w Rods are much larger and less numerous than in humans, making vision less acute

Sharks w Eyes still good, can see well in dim light, can see colors

Olfaction Taste

Sense of Smell

Most Fishes w Large olfactory bulb reflects importance of smell

Nostrils

Nostrils

Use of Smell w Recognize places in their environment
(migration) w Recognize each other as individuals w To communicate danger (alarm pheromone into the water if their skin is damaged) w In reproduction (pheromones released by females can trigger courting behavior in males) w To find food

Sharks w Excellent sense of smell w Use to locate potential prey (blood)

Salmon and Lamprey w Salmon use olfaction to detect proper stream (chemical signature) to enter for spawning w Lamprey use smell to locate juveniles in streams (to enter for spawning)

Sense of taste w Taste buds – used to detect food w Tongues, barbels, lips, face, entire body

Sense of taste w Catfishes have taste buds on barbels, entire body to locate food in murky waters

Sense of taste w Walleye have taste buds on lips, face w Can “taste” bait by “bumping” it without biting it

Lateral Line

Lateral Line

Lateral Line

Lateral Line w Connects scales to sensory cells and nerve fibers w Very important sensory organ

Contains mechanoreceptors that function similarly to mammalian inner ear Provides a fish with information concerning its movement through water or the direction and velocity of water flowing over its body

Same in Sharks w Canal system extending along sides and over head w Openings to surface, special sensory cells inside w Sensitive to vibrations, currents w Detect objects, moving animals

Other senses w Sharks also can detect electricity, which is emitted in small amounts by every living animal w May be more sensitive to electric fields than any other animal

Electroreception w Have special network of jelly-filled pits near snout called ampullae of Lorenzini to detect electric fields w Can pick up weak electrical stimuli from muscle contractions of animals

Ampullae of Lorenzini w May also serve to detect magnetic fields, which some sharks may use in navigation