Sensory SystemsSensory Systems

Sound, Lateral line, Electroreception, etc.Sound, Lateral line, Electroreception, etc.Chapter 6Chapter 6

MechanoreceptionMechanoreception

• Mechanoreception in fishes is largely involved in Mechanoreception in fishes is largely involved in the detection of motion of water. the detection of motion of water.

• PermitsPermits

“ “hearing” hearing” “balance” “balance”

“ “touch/feel” touch/feel” “gravity detection”“gravity detection”• System is divided into two basic components:System is divided into two basic components:

inner earinner ear lateral linelateral line• Sensory Sensory hair cellshair cells -basic unit (sensory apparatus -basic unit (sensory apparatus))

Inner ear structure & functionInner ear structure & function

• Pars superior - Pars superior - semicircular semicircular canalscanals– 3 canals arranged in three 3 canals arranged in three

dimensions (x, y, z axes)dimensions (x, y, z axes)– filled with viscous fluidfilled with viscous fluid– inner walls lined with naked inner walls lined with naked

hair cellshair cells– function to detect function to detect positionposition and and

movementmovement (inertia) (inertia)– input integrated with input input integrated with input

from utricle organ (utriculus - from utricle organ (utriculus - lapillus) for balancelapillus) for balance

• Pars superior - semicircular canalssemicircular 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

Inner ear structure & function

Inner Ear of FishesInner Ear of Fishes Lateral View. SC= Lateral View. SC= Semicircular Semicircular Canals, U= Canals, U= Utriculus, Utriculus, UO=Utricular UO=Utricular Otolith or Lapillus, Otolith or Lapillus, M=Macula, M=Macula, SU=Sulcus, SU=Sulcus, S=Sacculus, S=Sacculus, SO=Saccular SO=Saccular Otolith or Sagitta, Otolith or Sagitta, L=Lagena, L=Lagena, LO=Lagenar LO=Lagenar Otolith or Otolith or Asteriscus. Asteriscus. Modified from Modified from Popper and Coombs Popper and Coombs (1982). (1982).

Inner Ear: OtolithInner Ear: Otolith

• Pars inferior - Pars inferior - otolithotolith organs organs– Three chambers, arranged anterior Three chambers, arranged anterior

to posterior, filled with viscous fluid.to posterior, filled with viscous fluid.– Within each chamber is a suspended Within each chamber is a suspended

otolith otolith – inner walls of chambers lined with inner walls of chambers lined with

naked hair cellsnaked hair cells• Composed of CaCOComposed of CaCO33 and protein and protein• Used in determining growth rateUsed in determining growth rate

– Translucent (mineral) – slow growthTranslucent (mineral) – slow growth– Opaque (organic) – fast growthOpaque (organic) – fast growth– Daily rings – rapid growing fishDaily rings – rapid growing fish

• Shape is species specificShape is species specific• Highly resistant to digestionHighly resistant to digestion

micrograph of anglefish ootolithsmicrograph of anglefish ootoliths

Weberian Apparatus - enhanced sensitivity of Weberian Apparatus - enhanced sensitivity of hearinghearing

• Found only in Ostariophysi Found only in Ostariophysi (minnows, catfishes, (minnows, catfishes, characins)characins)

• Apparatus is made of Apparatus is made of modified pleural ribsmodified pleural ribs of first of first four vertebraefour vertebrae

• Sound waves impinge on Sound waves impinge on swim bladder and make it swim bladder and make it vibratevibrate

• swim bladder vibrations swim bladder vibrations transmitted mechanically by transmitted mechanically by W.A. to pars inferiorW.A. to pars inferior

Sound Production by fishesSound Production by fishes

• StridulatoryStridulatory (grinding) mechanisms (grinding) mechanisms– pharyngeal teeth (grunts)pharyngeal teeth (grunts)

– spine erection and locking (catfish, triggerfish)spine erection and locking (catfish, triggerfish)

– skull grinding against vertebrae (seahorses)skull grinding against vertebrae (seahorses)

– resonance of grinding by swim bladder for more harmonics (clicks and resonance of grinding by swim bladder for more harmonics (clicks and scratches become croaks and grunts)scratches become croaks and grunts)

• Swim bladderSwim bladder sounds sounds– resonation of stridulatory sounds (catfish)resonation of stridulatory sounds (catfish)

– belching or gulping – physostomes (remember pneumatic duct)belching or gulping – physostomes (remember pneumatic duct)

– ““strumming” - rubbing muscles against side of swim bladderstrumming” - rubbing muscles against side of swim bladder

– ““whistles” - muscles pull against wall of swim bladder to cause whistles” - muscles pull against wall of swim bladder to cause vibrationsvibrations

Ability to make sounds by fishesAbility to make sounds by fishes

• Hydromechanical sound production - low roarHydromechanical sound production - low roar– analogous to air rush associated with passing analogous to air rush associated with passing

traintrain– caused by rapid water displacementcaused by rapid water displacement

• due to undulation or turningdue to undulation or turning• noise from turbulent flow, e.g. in fast noise from turbulent flow, e.g. in fast

swimmingswimming– especially used by schooling fishespecially used by schooling fish

Acoustic-lateralis system in fishesAcoustic-lateralis system in fishes“the lateral line”“the lateral line”

““The feeling IS mutualThe feeling IS mutual...”...”

• Locations:– Lateral (side) canal

– Supraorbital (above eye) canal

– Infraorbital (below eye) canal

– Hyomandibular (lower jaw) canal

Only works in water! (Surprise!)

Senses movement of Important for:

Detecting prey Avoiding predators Schooling Interpret surroundings

Hair cell—cilia on

exposed surface of cell

Kinocilium—long, serves

as trigger

Stereocilia–shorter graded,

serve to condition

kinocilium for being

triggered

Neuromast—group of hair cells bundled together

Cupula—gelatinous sheath over cilia of hair cells in neuromast

Structure of Lateralis CanalsStructure of Lateralis Canals

• Epidermal tunnelEpidermal tunnel

• Pores open from canal to Pores open from canal to skin surfaceskin surface

• NeuromastsNeuromasts distributed distributed within tunnelwithin tunnel

• Fluid in tunnel is Fluid in tunnel is moremore viscous than water; viscous than water; therefore, more resistant therefore, more resistant to flowto flow

Structure of Lateralis CanalsStructure of Lateralis Canals

• Movement of water Movement of water outside fish causes outside fish causes displacement of fluid in displacement of fluid in canalcanal

• Canal fluid motion Canal fluid motion causes bending of causes bending of neuromast, firing of hair neuromast, firing of hair cells, triggers message to cells, triggers message to CNSCNS

• Sensitive to low freq. Sensitive to low freq.

(10 - 200 Hz)(10 - 200 Hz)

More on lateral line...More on lateral line...

• Primitive fish = lateral line possesses multiple Primitive fish = lateral line possesses multiple branchesbranches

• Modern fish = reduced to single line along the side Modern fish = reduced to single line along the side of the body and isolated pores on the headof the body and isolated pores on the head

• In sharks: lateral line present but not obvious on In sharks: lateral line present but not obvious on the side of the bodythe side of the body

Sometimes water and electricity DO mix...Sometimes water and electricity DO mix...

Why do fish need electricity?Why do fish need electricity?

• Electrical currents are carried with great efficiency in Electrical currents are carried with great efficiency in water due to density and salt content, water makes an water due to density and salt content, water makes an excellent medium for this action.excellent medium for this action.

• Used not only in prey detection, navigation, and Used not only in prey detection, navigation, and communication, but has been modified for defensive communication, but has been modified for defensive purposes in several species.purposes in several species.

Electric Field Production by FishesElectric Field Production by Fishes

• Electric field produced by Electric field produced by modified muscle cellsmodified muscle cells (electrocytes) - often much of body musculature(electrocytes) - often much of body musculature

• Electrocytes are disc-shaped and stacked in columnsElectrocytes are disc-shaped and stacked in columns

• Stimulation of electrocytes causes depolarization of Stimulation of electrocytes causes depolarization of cells - small electric current - stack of cells functions cells - small electric current - stack of cells functions like batteries in serieslike batteries in series

Uses of electroreceptionUses of electroreception

• Prey detectionPrey detection

...detect electromagnetic field produced by ...detect electromagnetic field produced by prey...prey...

• extremelyextremely sensitive: voltage gradient of sensitive: voltage gradient of 0.01 - 0.1 microvolts/cm,0.01 - 0.1 microvolts/cm,

...or detect prey distortion of self-induced ...or detect prey distortion of self-induced field from Electric Organ Discharge field from Electric Organ Discharge (EOD)(EOD)

Uses of electroreceptionUses of electroreception

• NavigationNavigation

– detect distortion of self-induced field from normal body detect distortion of self-induced field from normal body functions by moving through another electromagnetic functions by moving through another electromagnetic field, including Earth’s – Chondrichthyesfield, including Earth’s – Chondrichthyes

– Slight movement of magnetite crystal in skull against hair Slight movement of magnetite crystal in skull against hair cells – similar to otolith function cells – similar to otolith function

- some Osteichthyes- some Osteichthyes

ElectrolocationElectrolocation

Uses of electroreceptionUses of electroreception• CommunicationCommunication

– Electrical signals are species-specificElectrical signals are species-specific

– Used to signal species, sex, size, maturation state, location, distance, Used to signal species, sex, size, maturation state, location, distance, individual recognition, courtship, dominance, warnings, etc.individual recognition, courtship, dominance, warnings, etc.

– Modify pulse frequency, voltage, field shape as part of the Modify pulse frequency, voltage, field shape as part of the “vocabulary” for communication“vocabulary” for communication

Examples: Examples:

Mormyrids-elephantfishMormyrids-elephantfish

Gymnotids-knifefishesGymnotids-knifefishes

Siluriformes-catfishSiluriformes-catfish

Rajidae-skatesRajidae-skates

Chondrichthyes-sharksChondrichthyes-sharks

Sensory organs used in electroreceptionSensory organs used in electroreception

• Ampullary organsAmpullary organs (low frequency detection) (low frequency detection)

– ampullae of Lorenziniampullae of Lorenzini in sharks (Chondrichthyes), in sharks (Chondrichthyes), lungfishes (Sarcopterygii), sturgeons (Actinopterygii)lungfishes (Sarcopterygii), sturgeons (Actinopterygii)

– pit organspit organs in some teleosts (catfish, knifefish, in some teleosts (catfish, knifefish, elephantfish)elephantfish)

– gel-filled canal (conductive)gel-filled canal (conductive)

– lining of canal with closely-spaced, flattened, high-lining of canal with closely-spaced, flattened, high-resistance cells (no gaps - no current leakage)resistance cells (no gaps - no current leakage)

– receptor cells at base of ampule - depolarization receptor cells at base of ampule - depolarization causes Cacauses Ca2+2+ flux, causing release of neurotransmitter flux, causing release of neurotransmitter to sensory neuronto sensory neuron

Ampullae of Lorenzini trivia... Ampullae of Lorenzini trivia...

• Canal varies in length relative to the salinity of the Canal varies in length relative to the salinity of the environmentenvironment

-Saltwater elasmobranchs = long canals-Saltwater elasmobranchs = long canals-Freshwater elasmobranchs = short canals-Freshwater elasmobranchs = short canals

Sensory organs used in electroreceptionSensory organs used in electroreception

• Tuberous organsTuberous organs

– detect only detect only highhigh frequency & low voltage AC fields frequency & low voltage AC fields

– found in fishes that produce Electric Organ found in fishes that produce Electric Organ Discharge (EOD):Discharge (EOD):

• knifefishes (Gymnotidae)knifefishes (Gymnotidae)

• elephantfishes (Mormyridae)elephantfishes (Mormyridae)

Sensory organs used in electroreceptionSensory organs used in electroreception

• Tuberous organsTuberous organs

– bud-shaped swelling in epidermisbud-shaped swelling in epidermis

– receptor cells constantly depolarized by self-induced receptor cells constantly depolarized by self-induced EOD, causing release of neurotransmitter to sensory EOD, causing release of neurotransmitter to sensory neuronneuron

– detects changes in EOD-induced field by change in detects changes in EOD-induced field by change in the frequency of sensory impulses to brain - the frequency of sensory impulses to brain - PHASIC receptorPHASIC receptor

Types of Electric FieldsTypes of Electric Fields

• WeakWeak electric fields (EOD-induced) electric fields (EOD-induced)

– require intricate coordination - enlarged portion require intricate coordination - enlarged portion of cerebellum (metencephalon)of cerebellum (metencephalon)

– measure in millivolts/cmmeasure in millivolts/cm

– used for communication, prey detectionused for communication, prey detection

Black ghost knifefish, Black ghost knifefish, Apteronotus albifronsApteronotus albifrons

Electric fishElectric fish

•Gymnotiforms in S. America (L)Gymnotiforms in S. America (L)

•Mormyriforms in Africa (R)Mormyriforms in Africa (R)

•Found in muddy or black waterFound in muddy or black water

•Note long tail in both groupsNote long tail in both groups

Types of Electric FieldTypes of Electric Field

• StrongStrong electric fields (EOD-induced) electric fields (EOD-induced)

– 10’s to 100’s of volts (stunning)10’s to 100’s of volts (stunning)

torpedo rays (20 - 50 volts)torpedo rays (20 - 50 volts)

electric catfish (300 volts)electric catfish (300 volts)

electric eel* (500 volts!)electric eel* (500 volts!)

*Enough to knock a human unconscious or *Enough to knock a human unconscious or at least flatten you out...at least flatten you out...

Wave vs pulse EOD speciesWave vs pulse EOD species

Vision in FishesVision in Fishes

3-dimensional vision in a dim, dense, filtered environment3-dimensional vision in a dim, dense, filtered environment

Eye of southern flounder: courtesy of David Mowery

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 absorbs long wavelength (low frequency) more readily than short wavelengthsreadily than short wavelengths• red drops out in shallow water

• blue penetrates to greatest depths

Visual adaptations...Visual adaptations...• Lense specializationsLense specializations::

– spherical shapespherical shape FOCUSFOCUS

– protruding positionprotruding positionACUITYACUITY

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

Adaptations for vision in waterAdaptations for vision in water

• Retinal specializations:

– High density of rods—good in low lightHigh density of rods—good in low light

– Choroid gland maintains elevated OChoroid gland maintains elevated O22

levels in fish retinal tissue (levels in fish retinal tissue (rete mirabile)rete mirabile)

– Shallow species have more cones (why??)Shallow species have more cones (why??)

– Specialized pigments for blue end of Specialized pigments for blue end of

spectrumspectrum

– Tapetum lucidum reflective, enhances low

light vision

Smell (Olfaction)

Taste!!Taste!!

Fish tast buds are located on: head, mouthFish tast buds are located on: head, mouthSometimes...all over body for catfish!Sometimes...all over body for catfish!