1. Sensory Systems Sound, Lateral line, Electroreception, etc. Chapter 6

2. Mechanoreception
Mechanoreception in fishes is largely involved in the detection of motion of water.
Facilitates: “hearing” “balance”
“touch/feel” “gravity detection”
System is divided into two basic components:
inner ear lateral line

3. Inner ear structure & function
Pars superior - semicircular canals
3 canals arranged in three dimensions (x, y, z axes)
contain viscous fluid
canal lined w/ hair cells
detects position and movement (inertia)

4. Inner Ear: Otolith Otolith organs
Within each chamber is a suspended otolith
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

7. Weberian Apparatus - enhanced sensitivity of hearing
Found only in Ostariophysi (minnows, catfishes, characins)
Modified pleural ribs first four vertebrae
Sound waves impinge on swim bladder and make it vibrate
Swim bladder vibrations transmitted mechanically by W.A. to otolith

8. Sound Production by fishes
Stridulatory (grinding) mechanisms
pharyngeal teeth (grunts)
spine erection and locking (catfish, triggerfish)— “popping”
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

9. More sounds… Hydromechanical - low roar
-caused by rapid water displacement
due to undulation or turning
noise from turbulent flow, e.g. in fast swimming
especially used by schooling fish

10. Different Fish Sounds…
Different Fish Sounds…
Obeta
“Creaking”
Barge (topsail catfish)
Seacat
Toadfish pulse!!
“Grunt” “Drumming”

11. Acoustic-lateralis system in fishes “the lateral line”
“The feeling IS mutual...”

12. Only works in water! (Surprise!) 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

13. Neuromast—group of hair cells bundled together
Cupula—gelatinous sheath over cilia of hair cells in neuromast
Hair cell—cilia on
exposed surface of cell
Basic funcional unit of lateral line.

14. 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

15. 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.
( Hz)

16. 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

17. Sometimes water and electricity DO mix...
Electroreception
Sometimes water and electricity DO mix...

18. Why do fish need electricity?
Electrical currents are carried with great efficiency
Salt content of water also helps.
Water advantageous!
Prey detection
Navigation
Communication
Defense

19. 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

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

21. Uses of electroreception
Navigation
detect distortion of self-induced field from normal body functions by moving through another electromagnetic field, including Earth’s – Chondrichthyes
Slight movement of magnetite crystal in skull against hair cells – similar to otolith function
- some Osteichthyes

22. 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.

23. 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

24. 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

26. Ampullae of Lorenzini trivia...
Canal varies in length relative to the salinity of the environment
-Saltwater elasmobranchs = long canals
-Freshwater elasmobranchs = short canals

27. 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)

28. Types of Electric Fields
Weak electric fields (EOD-induced) (millivolts)
require intricate coordination - enlarged portion of cerebellum (metencephalon)
used for communication, prey detection
Black ghost knifefish, Apteronotus albifrons

30. Electric fish Gymnotiforms S. America (L) Mormyriforms African (R)
Found in muddy or “black”
water
Note long tail in both
groups

31. Types of Electric Field
Strong electric fields (EOD-induced)
10’s to 100’s of volts (stunning)
torpedo rays ( volts)
electric catfish (300 volts)
electric eel* (500 volts!)
*Enough to knock a human unconscious or at least flatten you out...

32. 3-dimensional vision in a dim, dense, filtered environment
Vision in Fishes
3-dimensional vision in a dim, dense, filtered environment
Eye of southern flounder: courtesy of David Mowery

33. 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

34. Visual adaptations... Lense specializations: spherical shape FOCUS
protruding position ACUITY
moveable position, off-center
NEAR- AND FARSIGHTED!

35. Adaptations for vision in water
Retinal specializations:
High density of rods—good in low light
Choroid gland maintains elevated O2 levels in fish retinal tissue (rete mirabile)
Shallow species have more cones (why??)

36. together to provide maxium visual accuity over a maximum
Rods and cones work
together to provide maxium
visual accuity over a maximum
range of light conditions.
Specialized pigments for blue end of spectrum
Tapetum lucidum reflective, enhances low light vision

37. Smell (Olfaction)

38. Taste!! Fish tast buds are located on: head, mouth
Sometimes...all over body for catfish!