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BIO224 - ichthyology > fish senses > Flashcards

fish senses Flashcards

1
Q

6 fish senses

A

Sight -> only good in close range
Smell (olfaction)
Taste (gustation)
Touch
Sound -> travels very well underwater
Electroreception

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2
Q

explain the sight sense in fish

A
  • Visible light = 400 – 700nm
  • Some fish can see UV
  • Light in water = unidirectional – only comes from above
  • Light in water = attenuated through absorption and scattering - Intensity declines with depth
  • Shorter wavelengths transmitted better - so red light absorbed first, blue/green absorbed last
  • Pigments in water also affects absorption
  • Oceanic blue/green (470-480), coastal (500-530nm) freshwater (550-560)
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3
Q

main difference between Stereotypical vertebrate eye and a fish’s

A

Stereotypical vertebrate = Elastic lens– stretched by ciliary muscle allowing eye to focus
Fish’s = Solid + more spherical lens – moves backwards + forwards using retractor lentis muscle

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4
Q

how do fish control the light entering the eye

A

Elasmobranchs and a few teleosts have contractile irises (react very slowly, though)
Other mechanisms:
Pigments in cornea
Operculum
Nictitating membrane

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5
Q

retina characteristics

A
  • Retina has a high O2 consumption
  • It is backed by a nutritive choroid
  • Choroid has a choroid gland (a rete mirabile) to maintain high O2 levels in retina
  • Elasmobranchs and some teleosts have a Tapetum lucidum - layer of reflecting guanine platelets behind the retina
  • rod + cone Photoreceptive cells
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6
Q

what’s Tapetum lucidum

A

layer of reflecting guanine platelets behind the retina that Elasmobranchs and some teleosts have

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7
Q

2 Photoreceptive cells in fish’s retina and how do these vary depending on the type of fish

A

Rod cells : more sensitive to low light
Cone cells : for detail and colour vision
- Diurnal (daytime) feeders have high cone:rod ratio
- Lower light inhabitants have twin cones (2 or more cells linked to 1 nerve ganglion to amplify signal)
- Nocturnal and mesopelagic fish have more rods than cones, often with many rods per ganglion
- Dark adapted: Rods close to surface, cones and melanin deeper
- Light adapted: Cones close to surface, rods deeper surrounded by melanin

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8
Q

eye characteristics of Mesopelagic (deep sea) fish in dysphotic zone

A

Very large eyes
Retinas with high density of rods
Large pupils and lenses
Adapted to blue/green 470-480nm (chryopsin)
Often tubular, fixed eyes

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9
Q

what are Tubular eyes

A

tubular shaped eye with same size lens + eye e.g. hatchet fish

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10
Q

advantages and disadvantages of Tubular eyes

A

Advantages:
- Allow smaller fish to possess larger lenses
- Good binocular vision but in one direction only - the main axes of the eye are nearer parallel than in normal eyes
- Some tubular eyes have vertical axes to see prey silhouetted above
Disadvantages:
- Fixed so can only view straight ahead – ability to view in other direction is sacrificed
- Peripheral retina is too near lens for adequate focal length so poor focus

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11
Q

adaptation of fish with tubular eyes that give them a bigger field of view

A
  • Valenciennellus: has an accessory retina that still receives light through the main lens – allows to extend their visual field even with fixed tubular eye
  • Spookfish - have an accessory retina as well as a lensless ocular diverticulum – entirely sperate part of the eye that looks down - mirror Reflects + focuses the light onto retina
  • Scopelarchus analis have secondary lens to focus light from beneath onto accessory retia - gives about 330° field of view
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12
Q

what are Warmer eyes

A
  • Warming the retina significantly improves temporal resolution, and the detection of rapid motion
  • Heat-assisted eyes work >10x faster than those cooled to the coldest deep-sea temperatures of around 3 °C
  • In swordfish, sailfish, marlin and the butterfly kingfish, the heat is produced by specialised extraocular muscles
  • Heat is retained in all using retia mirabilia
  • Tuna and lamnid sharks lack these extraocular muscle
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13
Q

how do fish use chemical senses

A

olfaction
- Pits lined with sensitive, olfactory epithelium folded and convoluted into a rosette
- There is usually 1 pair of connected nares (openings) each side of the head (incurrent + excurrent)
- Nostrils in fish are NOT respiratory

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14
Q

3 ways Flow through the nostrils occur

A

forward motion of the fish
ciliary action
muscular pumping

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15
Q

5 things Olfaction is used for

A

1.Food location
2. Migration (salmon use olfactory memory of natal river)
3. Presence of predators
4. Alarm substance (e.g. cypriniformes)
5. Social behaviour:
i. Recognition of opposite sex
ii. Stimulation of courtship behaviour

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16
Q

explain Gustation (taste) in fish

A
  • Similar to olfaction but separate system of taste buds
  • In elasmobranchs, confined to mouth and pharynx
  • In teleosts, all over but mainly palate, lips, barbels and lower part of head
  • Very sensitive and used in food SELECTION, especially where olfaction is used in food location (Note the difference)
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17
Q

what do taste senses in fish react to

A

Bitter
Sweet
Salt
Sour
Amino acids
Carbon dioxide

18
Q

what is the Acoustico-lateralis system

A
  • Detect things moving around (water motion)
  • both Ear (Acoustico) and lateral line (lateralis) system
  • Both use hair cells - extremely sensitive mechanoreceptors - found in Lateral line in fishes and amphibians + Organ of hearing in all vertebrates
19
Q

where are hair cells found

A
  • Lateral line in fishes and amphibians
  • Organ of hearing in all vertebrates
20
Q

explain the Lateral line system

A
  • The kinocilium and stereocilia of several hair cells embedded in a gelatinous cupula
  • Hair cells respond to deformation of cupula caused by water movement (vibration)
  • Whole organ known as a neuromas
  • Neuromasts are found in canals on the head + canals extending along side of body; the LATERAL LINE
  • Canals are connected to surrounding water through pores
  • Source of vibration can be obtained by comparing responses of different neuromasts along lateral line
  • Displacement of <2nm can be detected - movement up to 30m away
  • Prone to near-field effects (noise) from fishes own body, hence in canal and often displaced away from fins
21
Q

4 Functions of lateral line

A

Prey detection
Awareness of currents (rheotaxis)
Avoiding obstacles/predators
Schooling

22
Q

explain the Acoustico part (ears) of the Acoustico-lateralis system

A
  • Fish do not have external ears – sound has to travel through body tissues to get to nerves
  • Inner ear consists of a membraneous sac with 3 semicircular canals and bony chambers (utriculus, saccules, laguna), in either side of head
    -canals = Detect dynamic equilibrium (with ampullae)
    -chambers = Detect static equilibrium (with otoliths)
  • Semi-circular canals contain a fluid called endolymph + ampullae
  • Ampullae contain hair cells on ridges which project into lumen of ampulla and respond to movement of endolymph (dynamic equilibrium)
23
Q

what are fish ears used for

A
  • positioning with respect to gravity (static equilibrium)
  • angular acceleration (dynamic equilibrium)
  • hearing
24
Q

what are otoliths

A

bony structures that measure the fishes reference
to gravity (static equilibrium) - particularly the lapillus
- Each otolith lies on a bed of hair cells called a macula
- Otoliths also respond to sound (pressure) waves (especially the sagitta)
- They are more dense than surrounding fish tissue, so respond more slowly to pressure waves, triggering the hair cells
- Swimbladders can magnify sound waves to improve hearing
- Many fish have therefore evolved a connection between their ‘ears’ and their swimbladder e.g. Clupeids (herring family) have a canal
- Ostariophysi (carps & catfish) have a chain of modified vertebrae
- can be used to age a fish

25
Q

3 named otoliths in a fish’s ear

A

sagitta
lapillus
astericus

26
Q

how can otoliths be used to age a fish

A

Otoliths reflect seasonality in growth of fish
- Summer growth = dense “opaque” zone
- Winter growth = less dense “hyaline” zone
- One pair of rings (1 opaque zone + 1 hyaline zone) = 1 year’s growth

27
Q

do elasmobranchs have otoliths

A

not bony fish - so do not have calcareous otoliths
- Have sand particles in a mucus jelly that do the same job
- But we can’t age them

28
Q

Incidental sounds that fish make

A

swimming/feeding noises
initiate feeding
prey detection
predator avoidance

29
Q

Intentional sounds fish make

A
  • Stridulation
    i. scraping pharyngeal teeth
    ii. spines/fin rays
    iii. Swimbladder can act as resonator
  • Swimbladder and extrinsic muscles - Vibration of muscles attached to wall of swimbladder, e.g. drums and croakers (Sciaenids)
  • Swimbladder and intrinsic muscles - Vibration of muscles within wall of swimbladder e..g. cod, pollack, haddock and gurnards
  • Gas expulsion from physostomatous swimbladder (e.g. eels and some carp)
30
Q

how many species of fish produce sound

A

> 800

31
Q

what are Electrogenic fish

A

fish that create electric fields

32
Q

what are Electroreceptive fish

A

fish that can detect electric fields

33
Q

4 main ways fish use electricity

A
  • Navigation - create electric fields around themselves to navigate, this is especially useful in turbid/murky waters
  • Hunting - detection of microvolts generated by small muscle contractions; some (e.g. electric eels) can stun prey
  • Defence – stunning or killing of potential predators; hypopomid electric fish produce broad frequency electric fields to prevent detection by electroreceptive fish
  • Communication - Electrical signals can be sent to warn males and during courtship with females
34
Q

what receptors do most Electroreceptive fish use

A

Ampullary (tonic) receptors
- Ampullae of Lorenzini found in all elasmobranchs + some teleosts (some catfish, sturgeons, paddle fish, lungfish)

35
Q

what are Ampullae of Lorenzini and what are they used for

A
  • Sensory cells sensitive to electrical stimulus of low frequency (0.05-8Hz) + mechanical stimulation and changes in salinity and temperature
  • located around head of sharks, all over body of catfish, on pectoral ‘wings’ of ray
  • Prey detection - cells are constantly receptive to low frequency stimulus from weak action potentials of muscle and nerve fibres in prey animals
36
Q

what are Tuberous or Phasic receptors

A
  • Receptor cells that some fish have - show a brief response to a high frequency stimulus
  • found in electric fishes such as gymnotids (knife fishes) and mormyrids (elephant-nose fish)
  • Similar to Ampullae of Lorenzini but no ‘apparent’ canal to surface
37
Q

main difference between Ampullae of Lorenzini and Tuberous or Phasic receptors

A

their adaptation to use:
- Tonic (ampullary) receptors used to detect prey
- Phasic receptors to register high frequency discharge from electric organs in other fish

38
Q

what are Electric organs

A

Stacks of modified muscle or nerve cells used just to generate electricity e.g Electrophorus electric eel, Malapterus electric catfish
- Action potentials between individual plates is small, 0.1- 0.15 volts, but in series, as in a battery, are additive and can generate many volts

39
Q

functions of electric organs

A
  • Protection - A danger to anyone handling such fish, rubber gloves & wellington boots essential wear
  • Stunning prey - Functions of electric organs
  • But also used for electro-location of prey and position - requires generating an electric field and identifying distortions in field by phasic receptors generated by surrounding objects
40
Q

what is necessary to avoid creating your own distortions in electric field

A

remain rigid and swim using just fins running length of body

41
Q

where is Electro-location mostly used

A

in murky freshwater (where eyes are not much use) - seawater loses discharge rapidly and thought to just use for intraspecific signalling

42
Q

what happens to an Electric current in any conductor moving through a magnetic field

A

it’s induced - Seawater (but not freshwater) is a sufficiently good conductor for elasmobranchs (at least) to use their Ampullae of Lorenzini to detect the Earth’s magnetic field (magnetoreception) for migration

BIO224 - ichthyology (13 decks)

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