Sensory Systems Sound, Lateral line, Electroreception, etc' Chapter 6

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Sensory SystemsSound, Lateral line,
Electroreception, etc.Chapter 6
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Mechanoreception

• Mechanoreception in fishes is largely involved in
  the detection of motion of water.
• Permits
• hearing balance
• touch/feel gravity detection
• System is divided into two basic components
• inner ear lateral line
• Sensory hair cells -basic unit (sensory
  apparatus)

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Inner ear structure function

• Pars superior - semicircular canals
• 3 canals arranged in three dimensions (x, y, z
  axes)
• filled with viscous fluid
• inner walls lined with naked hair cells
• function to detect position and movement
  (inertia)
• input integrated with input from utricle organ
  (utriculus - lapillus) for balance

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Inner ear structure function

• Pars superior - semicircular canals
• 3 canals arranged in three dimensions (x, y, z
  axes)
• filled with viscous fluid
• inner walls lined with naked hair cells
• function to detect position and movement
  (inertia)
• input integrated with input from utricle organ
  (utriculus - lapillus) for balance

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Inner Ear of Fishes Lateral View. SC
Semicircular Canals, U Utriculus, UOUtricular
Otolith or Lapillus, MMacula, SUSulcus,
SSacculus, SOSaccular Otolith or Sagitta,
LLagena, LOLagenar Otolith or Asteriscus.
Modified from Popper and Coombs (1982).
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Inner Ear Otolith

• Pars inferior - otolith organs
• Three chambers, arranged anterior to posterior,
  filled with viscous fluid.
• Within each chamber is a suspended otolith
• inner walls of chambers lined with naked hair
  cells
• Composed of CaCO3 and protein
• Used in determining growth rate
• Translucent (mineral) slow growth
• Opaque (organic) fast growth
• Daily rings rapid growing fish
• Shape is species specific
• Highly resistant to digestion

micrograph of anglefish ootoliths
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Weberian Apparatus - enhanced sensitivity of
hearing

• Found only in Ostariophysi (minnows, catfishes,
  characins)
• Apparatus is made of modified pleural ribs of
  first four vertebrae
• Sound waves impinge on swim bladder and make it
  vibrate
• swim bladder vibrations transmitted mechanically
  by W.A. to pars inferior

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Sound Production by fishes

• Stridulatory (grinding) mechanisms
• pharyngeal teeth (grunts)
• spine erection and locking (catfish, triggerfish)
• skull grinding against vertebrae (seahorses)
• resonance of grinding by swim bladder for more
  harmonics (clicks and scratches become croaks and
  grunts)
• Swim bladder sounds
• resonation of stridulatory sounds (catfish)
• belching or gulping physostomes (remember
  pneumatic duct)
• strumming - rubbing muscles against side of
  swim bladder
• whistles - muscles pull against wall of swim
  bladder to cause vibrations

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Ability to make sounds by fishes

• Hydromechanical sound production - low roar
• analogous to air rush associated with passing
  train
• caused by rapid water displacement
• due to undulation or turning
• noise from turbulent flow, e.g. in fast swimming
• especially used by schooling fish

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Acoustic-lateralis system in fishesthe lateral
line

• The feeling IS mutual...

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Only works in water! (Surprise!) Senses movement
of Important for Detecting prey Avoiding
predators Schooling Interpret surroundings

• Locations
• Lateral (side) canal
• Supraorbital (above eye) canal
• Infraorbital (below eye) canal
• Hyomandibular (lower jaw) canal

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Neuromastgroup of hair cells bundled
together Cupulagelatinous sheath over cilia of
hair cells in neuromast

• Hair cellcilia on
• exposed surface of cell
• Kinociliumlong, serves
• as trigger
• Stereociliashorter graded,
• serve to condition
• kinocilium for being
• triggered

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Structure of Lateralis Canals

• Epidermal tunnel
• Pores open from canal to skin surface
• Neuromasts distributed within tunnel
• Fluid in tunnel is more viscous than water
  therefore, more resistant to flow

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Structure of Lateralis Canals

• Movement of water outside fish causes
  displacement of fluid in canal
• Canal fluid motion causes bending of neuromast,
  firing of hair cells, triggers message to CNS
• Sensitive to low freq.
• (10 - 200 Hz)

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More on lateral line...

• Primitive fish lateral line possesses multiple
  branches
• Modern fish reduced to single line along the
  side of the body and isolated pores on the head
• In sharks lateral line present but not obvious
  on the side of the body

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Electroreception

• Sometimes water and electricity DO mix...

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Why do fish need electricity?

• Electrical currents are carried with great
  efficiency in water due to density and salt
  content, water makes an excellent medium for this
  action.
• Used not only in prey detection, navigation, and
  communication, but has been modified for
  defensive purposes in several species.

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Electric Field Production by Fishes

• Electric field produced by modified muscle cells
  (electrocytes) - often much of body musculature
• Electrocytes are disc-shaped and stacked in
  columns
• Stimulation of electrocytes causes depolarization
  of cells - small electric current - stack of
  cells functions like batteries in series

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Uses of electroreception

• Prey detection
• ...detect electromagnetic field produced by
  prey...
• extremely sensitive voltage gradient of 0.01 -
  0.1 microvolts/cm,
• ...or detect prey distortion of self-induced
  field from Electric Organ Discharge (EOD)

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Uses of electroreception

• Navigation
• detect distortion of self-induced field from
  normal body functions by moving through another
  electromagnetic field, including Earths
  Chondrichthyes
• Slight movement of magnetite crystal in skull
  against hair cells similar to otolith function
• - some Osteichthyes

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Electrolocation
If the object is less conductive than the water
(e.g., a rock), electric current will be shunted
around the object. This will give rise to a local
decrease in current density, which in turn
creates an "electrical dark spot" or "electrical
shadow" on the skin. If the object is more
conductive than the water (e.g., a minnow),
electric current will be shunted through the
object because it represents a path of lower
resistance. This will give rise to a local
increase in current density, which in turn create
an "electrical bright spot" on the skin.
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Uses of electroreception

• Communication
• Electrical signals are species-specific
• Used to signal species, sex, size, maturation
  state, location, distance, individual
  recognition, courtship, dominance, warnings, etc.
• Modify pulse frequency, voltage, field shape as
  part of the vocabulary for communication
• Examples
• Mormyrids-elephantfish
• Gymnotids-knifefishes
• Siluriformes-catfish
• Rajidae-skates
• Chondrichthyes-sharks

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Sensory organs used in electroreception

• Ampullary organs (low frequency detection)
• ampullae of Lorenzini in sharks (Chondrichthyes),
  lungfishes (Sarcopterygii), sturgeons
  (Actinopterygii)
• pit organs in some teleosts (catfish, knifefish,
  elephantfish)
• gel-filled canal (conductive)
• lining of canal with closely-spaced, flattened,
  high-resistance cells (no gaps - no current
  leakage)
• receptor cells at base of ampule - depolarization
  causes Ca2 flux, causing release of
  neurotransmitter to sensory neuron

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Ampullae of Lorenzini trivia...

• Canal varies in length relative to the salinity
  of the environment
• -Saltwater elasmobranchs long canals
• -Freshwater elasmobranchs short canals

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Sensory organs used in electroreception

• Tuberous organs
• detect only high frequency low voltage AC
  fields
• found in fishes that produce Electric Organ
  Discharge (EOD)
• knifefishes (Gymnotidae)
• elephantfishes (Mormyridae)

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Sensory organs used in electroreception

• Tuberous organs
• bud-shaped swelling in epidermis
• receptor cells constantly depolarized by
  self-induced EOD, causing release of
  neurotransmitter to sensory neuron
• detects changes in EOD-induced field by change in
  the frequency of sensory impulses to brain -
  PHASIC receptor

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Types of Electric Fields

• Weak electric fields (EOD-induced)
• require intricate coordination - enlarged portion
  of cerebellum (metencephalon)
• measure in millivolts/cm
• used for communication, prey detection

Black ghost knifefish, Apteronotus albifrons
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Electric fish

• Gymnotiforms in S. America (L)
• Mormyriforms in Africa (R)
• Found in muddy or black water
• Note long tail in both groups

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Types of Electric Field

• Strong electric fields (EOD-induced)
• 10s to 100s of volts (stunning)
• torpedo rays (20 - 50 volts)
• electric catfish (300 volts)
• electric eel (500 volts!)
• Enough to knock a human unconscious or at least
  flatten you out...

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Wave vs pulse EOD species
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Vision in Fishes

• 3-dimensional vision in a dim, dense, filtered
  environment

Eye of southern flounder courtesy of David Mowery
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Main Challenges...

• Water density-absorbs light differently than does
  the atmosphere - e.g. parallax at surface (bends
  light)
• Water is a dim medium due to high absorptive
  capacity - 10 or more lost in first meter of
  clear lake water
• Water absorbs long wavelength (low frequency)
  more readily than short wavelengths
• red drops out in shallow water
• blue penetrates to greatest depths

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Visual adaptations...

• Lense specializations
• spherical shape FOCUS
• protruding position ACUITY

• moveable position, off-center
• NEAR- AND FARSIGHTED!

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Adaptations for vision in water

• Retinal specializations
• High density of rodsgood in low light
• Choroid gland maintains elevated O2 levels in
  fish retinal tissue (rete mirabile)
• Shallow species have more cones (why??)
• Specialized pigments for blue end of spectrum
• Tapetum lucidum reflective, enhances low light
  vision

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Smell (Olfaction)
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Taste!!
Fish tast buds are located on head,
mouth Sometimes...all over body for catfish!