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

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

2. 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)

3. 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

4. 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

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

6. 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

8. 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

9. 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

10. 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

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

12. 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

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 Kinocilium—long, serves as trigger Stereocilia–shorter graded, serve to condition kinocilium for being triggered

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. (10 - 200 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. Electroreception Sometimes water and electricity DO mix...

18. 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.

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 0.01 - 0.1 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. 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

29. 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

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

32. Types of Electric Field • Strong electric fields (EOD-induced) • 10’s to 100’s 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...

33. Wave vs pulse EOD species

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

35. 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

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

37. 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??) • Specialized pigments for blue end of spectrum • Tapetum lucidum reflective, enhances low light vision

38. Smell (Olfaction)

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