Electric fish Flashcards
What is passive electrolocation? Example animals
Animal is electroreceptive only
Sharks, rays, catfish
What is active sense electrolocation? Examples
Animal generates its own electric field and can detect changes
Weakly electric fish and some strongly electic such as electric eel, ray and catfish
Animate source
Biological e.g. conspecifics, predators, prey of active sense animals
Inanimate source
Naturally occurring electric fields e.g. geomagnetic, electrochemical
Examples of elecroreceptive amphibians and a mammal
Salamanders and caecilians
Platypus
Evolutionary development and losses of electroreception…
Evolved by common ancestor of fish
Lost by many including teleoists
Re-evolved separately by mormyriforms and gymnotiforms
Re-evolved by monotremes (platypus)
How many groups of fish have convergently evolved electroreception? 4 examples and their names
Mormyriforms - african elephantfish
Gymnotiforms - south american knifefish
Malapteruidae - catfish
Torpediniformes - ray
Relative proportions of electroreceptive and electrogenic fish
25% electroreceptive
0.7% electrogenic
(out of 32000 species)
Examples within the two main groups of electric fish
Strongly electric
Electric eel, catfish and ray (~500-600V) to stun prey
Weakly electric
south american knifefish, african elephantfish (~10V) communication
Two types of electrical discharge. Which uses which?
Mormyriforms (african elephantfish) use pulse
Gymnotiforms (s.american knifefish) us wave
How is the EOD generated?
Electrocytes have -ve potential
Na/K exchanger pumps Na out
Impulse arriving causes ACh release
LGNCs open, Na influx is responsible for current
How are electrocytes arranged?
Into series to form electroplaques
Current flows +ve to -ve
How does stacking of electroctes aid function?
Formation of electroplaques allows for synchronous discharge and summation of current
They are insulated by connective tissue to force current through water (instead of body)
Which muscles generate EOD?
Tail muscle in weakly electric fish
Branchial muscles in electric rays
How do tentacled snakes bypass electroreception to catch fish?
They adopt a J shape and startle fish as they approach
Fish attempts to swim away but often swims into snakes mouth
How is EOD controlled?
By pacemaker nucleus in brain
Waveform is dependant on complexity of innervation of electrocyte
Monopolar in strongly electric
Bipolar or more in weakly electric fish
2 categories of electroreceptors
Ampullary (evolved in ancestral fish)
Tuberous (only in weak electric fish)
All are hair cells, mechanoreceptors
Describe the structure of an ampullary receptor (for passive electroreception)
A pit (lined with apical cells) filled with conductive gel and exposed sensory neurones at the bottom (on basement membrane)
Describe the functioning of ampullary receptors
Spontaneously active and sensitive to weak fields (1V in 2000km - marine. 1V in 10km - fresh water. Difference due to salt conductance in ocean)
Low frequency detection
Signal transmission from ampullary receptors
Receptor cell depolarised
NT released
Causes EPSP in sensory neurone
Describe the tuberous electroreceptor (for active electroreception)
Sensory cells within basement membrane Loose epidermal cover Time markers detect frequency Amplitude coders detect change in amplitude (high frequency detection)
Decribe the time marker in the tuberous electroreceptor
Single AP per EOD with fixed latency
1-35 receptor cells to one neurone
Used in passive electrolocation to detect fields of prey
Amplitude coders
Bursts of spikes produced
Latency of first spike encodes the amplitude
Latency = time between EOD and first spike
Key points of paper by Kalmijn
Shark put into agar chamber with covered flatfish
Shark located fish without vision
Little response to whiting pieces, none when smell removed with film
Bioelectric field of flatfish simulated with electrodes, eliciting same response
Shark preferred buried electrodes to visible whiting
Which fish families engage in active electrolocation?
Mormyrids (amplitude coders) and gymnotids (amplitude and time-marker coders)
Modification of brain areas for EOD
Reduction in other sensory areas
Somatotropic maps of electrosensitive body surface
Challenges with electrocommunication
Mormyrids experience interference with own EOD: corollary discharge inhibition of timing marker in pulse fish
Gymnotiforms experience interference from conspecifics: jamming avoidance response
Describe the jamming avoidance response
Two fish with similar frequencies will shift their frequencies to increase the difference between them, stopping the jamming of their electroreception
What does curare do and what is its use?
Blocks mAChRs to silence self EOD
Allows fish to assess neighbor fish EOD and respond by changing pacemaker firing frequency
Results of JAR
Self EOD frequency altered
Self fish monitors EOD frequency, not pacemaker firing for JAR
Uses receptors on body, not head to monitor EOD
How do receptors respond differently to self and neighbour EOD?
Receptors are present to detect same strength and different strengths of EOD
Strength of neighbor EOD will vary as distance from source and angle of receptors will differ (receptors perpendicular to field least activated)
Why is position of EOD source important to JAR?
Neighbour EOD electronically added to self EOD and played through self electrodes
Can’t perform JAR
Fish relies on differen filed characteristics cause by different EOD sources
Role of ampullary receptors
Tuned into DC and low frequency
AC signals are not in EOD range
e.g. sharks use to detect low freq. DC fields of prey
How do weakly electric fish use ampullary and tuberous receptors?
Detect the weakly electric fields produced by other fish
What do tuberous receptors encode?
Frequency and amplitude of EOD
Two types: time markers, T, and amplitude coders, P
Interpretation of self EOD
Time marker ‘T receptor’
Summation onto spherical cells
Convergence of info into Laminae of Torus semicircularis
Sharks use specialised ampullary receptors to
Detect prey’s low frequency DC fields
Weakly electric fish use their ampullary and tuberous receptors to
Detect weakly electric fields produced by neighbours
What is an efferent copy?
Internal copy of outflowing movement-producing signal generated by the motor system. This inhibits expected sensory feedback. The EOD inhibits knollenorganes as the EOD is expected to hit them so don’t detect own EOD
What is somatotopy?
Correspondence of an area of the body to a specific point on CNS. Receptor location represented as 4 somatotopic maps. Ampullary: 1. Tuberous projects to 3 maps.
How do fish use active electrolocation for location?
Objects cause change in current flow. Area of active receptors indicate objects location relative to body
Insulators reduce current and conductors increase, forming somatotopic maps
How do fish use active electrolocation for conductance?
Objects distort electric field created by EOD (amplitude increased or decreased)
How do fish use active electrolocation for distance?
Closer objects cause a larger change in amplitude
Far object produces large image with low contrast
Near object produces small image with high contrast
Uses single stationary array of receptors
How do fish use active electrolocation to determine capacitance?
Ability to store electrical charge
Organisms have high capacitance
Mormyrid (pulse) amplitude coders compare responses of A and B cells to determine capacitance
Gymnotids (wave) T receptors compare timing distortions at different positions on the body to determine capacitance
How does capacitance change the EOD
Modifies shape but not timing of EOD pulses in pulse-type mormyrids
In wave time gymnotids, it modified timing of field relative to emission
Other uses for EOD
Gender identification - males and females have different freq. ranges
Males modify EOD during courtship
Short low freq. chirps indicate aggression - long high freq. chirps indicate submissions
