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Electric fish

Electric fish. 746 Lecture 3. Aim. How fish Sense electric signals Generate electric signals Use in Prey detection Communication Electrolocation Self v non-self. Electroreception. Electric field properties Electroreception Bioelectric field production Electrolocation

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Electric fish

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  1. Electric fish 746 Lecture 3

  2. Aim • How fish • Sense electric signals • Generate electric signals • Use in • Prey detection • Communication • Electrolocation • Self v non-self

  3. Electroreception • Electric field properties • Electroreception • Bioelectric field production • Electrolocation • Electrocommunication

  4. Electric field Electric field indicates direction and magnitude of force Electric potential indicates whether a charge is attracted or repelled

  5. Electric field properties • Field shows which way an electron would move • Electric potential (measured in volts) is always perpendicular to electric field • Electric fields around a dipole fall off with the cube of distance • Electric fields are, therefore, not useful over long distances. Electro-communication operates over a few meters, electrolocation over a distance of less than 1 m.

  6. Bioelectric fields • All living animals produce very weak electric fields. • e.g. from heartbeat • These can be detected by a variety of predatory animals, • sharks, platypus, lungfish.

  7. Lungfish use bioelectric cues

  8. derived from hair cells sensitive to 0.01 µV/cm in marine species, 0.01 mV/cm in freshwater; DC fields or to frequencies less than 50 Hz Ampullary receptors

  9. Summary so far • Electric field in water • Sense for prey • Next: production of EOD • electric organ discharge

  10. Weakly electric fish

  11. EOD production • Electric organs contain 10-1000 electrocytes in series • Electrocytes • modified muscle or nerve cells • surrounded by connective tissue (insulator)

  12. Electric organs- control • Synchronized discharge makes EOD • Controlled by pacemaker nucleus

  13. Electric organ shapes

  14. EOD movies http://alumni.caltech.edu/~rasnow/qtmov.html

  15. Innervation • Electrocytes innervated on one face • EPSP followed by action potential

  16. Evolution

  17. Electric eel • Electrophorus electricus • Electric organ has up to 6000 electrocytes and produces 720 volts

  18. Summary so far • Electric field in water • Sense for prey • Generate electric field • electric organ discharge • Next: weakly electric fish

  19. Weakly electric fish • Much smaller voltages • use signals to • locate objects • communicate • Mormyrids • Gymnotids

  20. Wave vs pulse • puilses in African and some S American spp • waves in Eigenmannia Gnathonemus

  21. Geography

  22. Mormyrids • single pulses of signal • 2 time scales • very consistent

  23. Pulse shape = owner

  24. species sex status Shape indicates…

  25. JAR in Eigenmannia • Jamming avoidance response • both at 400Hz….

  26. How ? • signals originating inside, all in phase • signals from another fish, left and right in opposite phase

  27. Simulation

  28. EOD & courtship

  29. Electrolocation

  30. Field modification • The left frame shows the 3-d fish body. • The middle frame depicts the head-negative peak of the EOD • The rightmost frame shows the difference that the object makes:

  31. distance / size • small object • far off – big, weak shadow • close by – dense shadow “mexican hat” illusion

  32. Summary so far • Electric field in water • Sense for prey • Generate electric field • electric organ discharge • use for object location • use for social communication • Next: What do we know of the physiology of this behaviour ?

  33. Mormyrids have 3 kinds of electroreceptors knollenorgans mormyromasts ampullary - too small to see Electroreceptors

  34. Electroreceptors • different • anatomy • physiology - curarised fish • role in behaviour ampullary mormyromast knollenorgan

  35. Response to EOD A - variable K - 1 spike/EOD M - depends on strength

  36. EOD + object control + object no object ampullary mormyromast

  37. Central response • Electroreceptors project to ELL • Electrosensory Lateral Line Lobe

  38. ELL - Knollenorgan NB no ELL response zap Ko ELL - 1 ELL - 2 ELL - 3 EOCD

  39. ELL- mormyromast intra- ELL extra EOCD zap Mm zap Mm just after EOCD

  40. ELL - ampullary • Count ELL spikes with / without object near + + 5 min

  41. Efference copy • http://www.proberts.net/PROBERTS/CNS00/source/10.htm

  42. 3 receptors, 3 functions • Knollenorgan - • turn off at own EOCD • always signals someone else • Mormyromast • enhance at time of own EOCD • measure strength of electric field • find objects nearby • Ampullary • find objects by comparing expected with mirror image - efference copy

  43. Self v non-self

  44. Summary • Electric field in water • Sense for prey • Generate electric field • electric organ discharge • use for object location • use for social communication • control of receptor input to distinguish self from non-self, • using 3 different mechanisms

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