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 Electrocommunication

Electric field

Electric field indicates direction and magnitude of forceElectric potential indicates whether a charge is attracted or repelled

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.

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.

Lungfish use bioelectric cues

Ampullary receptors 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

Summary so far Electric field in water Sense for prey Next: production of EOD

electric organ discharge

Weakly electric fish

EOD production Electric organs contain 10-1000

electrocytes in series Electrocytes

modified muscle or nerve cells

surrounded by connective tissue (insulator)

Electric organs- control

Synchronized discharge makes EOD Controlled by pacemaker nucleus

Electric organ shapes

EOD movies

http://alumni.caltech.edu/~rasnow/qtmov.html

Innervation Electrocytes innervated on one face EPSP followed by action potential

Evolution

Electric eel Electrophorus electricus Electric organ has up to 6000

electrocytes and produces 720 volts

Summary so far Electric field in water Sense for prey Generate electric field

electric organ discharge Next: weakly electric fish

Weakly electric fish Much smaller voltages use signals to

locate objects communicate

Mormyrids Gymnotids

Wave vs pulse puilses in African

and some S American spp

waves in Eigenmannia

Gnathonemus

Geography

Mormyrids single pulses of signal

2 time scales very consistent

Pulse shape = owner

Shape indicates… species sex

status

JAR in Eigenmannia Jamming avoidance response

both at 400Hz….

How ? signals originating inside, all in phase signals from another fish, left and right

in opposite phase

Simulation

EOD & courtship

Electrolocation

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:

distance / size small object

far off – big, weak shadow close by – dense shadow

“mexican hat” illusion

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 ?

Electroreceptors Mormyrids have 3 kinds of

electroreceptors knollenorgans mormyromasts ampullary -

too small to see

Electroreceptors different

anatomy physiology - curarised fish role in behaviour

ampullary mormyromast knollenorgan

Response to EOD

K - 1 spike/EOD M - depends on strength

A - variable

EOD + object

control

+ object

no object

ampullary mormyromast

Central response Electroreceptors project to ELL

Electrosensory Lateral Line Lobe

ELL - Knollenorgan

EOCD

ELL - 3ELL - 2ELL - 1

zap Ko

NB no ELL response

ELL- mormyromast

zap Mm

EOCD

intra-ELL extra

zap Mm just after EOCD

ELL - ampullary Count ELL spikes with / without object

near

+

+ 5 min

Efference copy http://www.proberts.net/PROBERTS/CNS00/source/

10.htm

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

Self v non-self

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