fish senses Flashcards
6 fish senses
Sight -> only good in close range
Smell (olfaction)
Taste (gustation)
Touch
Sound -> travels very well underwater
Electroreception
explain the sight sense in fish
- 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)
main difference between Stereotypical vertebrate eye and a fish’s
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
how do fish control the light entering the eye
Elasmobranchs and a few teleosts have contractile irises (react very slowly, though)
Other mechanisms:
Pigments in cornea
Operculum
Nictitating membrane
retina characteristics
- 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
what’s Tapetum lucidum
layer of reflecting guanine platelets behind the retina that Elasmobranchs and some teleosts have
2 Photoreceptive cells in fish’s retina and how do these vary depending on the type of fish
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
eye characteristics of Mesopelagic (deep sea) fish in dysphotic zone
Very large eyes
Retinas with high density of rods
Large pupils and lenses
Adapted to blue/green 470-480nm (chryopsin)
Often tubular, fixed eyes
what are Tubular eyes
tubular shaped eye with same size lens + eye e.g. hatchet fish
advantages and disadvantages of Tubular eyes
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
adaptation of fish with tubular eyes that give them a bigger field of view
- 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
what are Warmer eyes
- 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
how do fish use chemical senses
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
3 ways Flow through the nostrils occur
forward motion of the fish
ciliary action
muscular pumping
5 things Olfaction is used for
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
explain Gustation (taste) in fish
- 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)
what do taste senses in fish react to
Bitter
Sweet
Salt
Sour
Amino acids
Carbon dioxide
what is the Acoustico-lateralis system
- 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
where are hair cells found
- Lateral line in fishes and amphibians
- Organ of hearing in all vertebrates
explain the Lateral line system
- 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
4 Functions of lateral line
Prey detection
Awareness of currents (rheotaxis)
Avoiding obstacles/predators
Schooling
explain the Acoustico part (ears) of the Acoustico-lateralis system
- 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)
what are fish ears used for
- positioning with respect to gravity (static equilibrium)
- angular acceleration (dynamic equilibrium)
- hearing
what are otoliths
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
3 named otoliths in a fish’s ear
sagitta
lapillus
astericus
how can otoliths be used to age a fish
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
do elasmobranchs have otoliths
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
Incidental sounds that fish make
swimming/feeding noises
initiate feeding
prey detection
predator avoidance
Intentional sounds fish make
- 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)
how many species of fish produce sound
> 800
what are Electrogenic fish
fish that create electric fields
what are Electroreceptive fish
fish that can detect electric fields
4 main ways fish use electricity
- 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
what receptors do most Electroreceptive fish use
Ampullary (tonic) receptors
- Ampullae of Lorenzini found in all elasmobranchs + some teleosts (some catfish, sturgeons, paddle fish, lungfish)
what are Ampullae of Lorenzini and what are they used for
- 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
what are Tuberous or Phasic receptors
- 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
main difference between Ampullae of Lorenzini and Tuberous or Phasic receptors
their adaptation to use:
- Tonic (ampullary) receptors used to detect prey
- Phasic receptors to register high frequency discharge from electric organs in other fish
what are Electric organs
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
functions of electric organs
- 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
what is necessary to avoid creating your own distortions in electric field
remain rigid and swim using just fins running length of body
where is Electro-location mostly used
in murky freshwater (where eyes are not much use) - seawater loses discharge rapidly and thought to just use for intraspecific signalling
what happens to an Electric current in any conductor moving through a magnetic field
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
