block 3- electric fish lol Flashcards
(23 cards)
different types of electric sense
-Passive sense (detect external electric fields)= if something touches you and you feel it you didn’t have to do anything to elicit that feeling
Active sense- Some fish create a weak electric field around themselves. When an object (like a rock or another fish) enters this field, it distorts the electricity. Special sensors on the fish’s skin detect these changes, helping them “see” their surroundings, even in dark or murky water. This works like feeling ripples in water without seeing them
how do fish generate electric discharge (EOD)
Electric fish generate electricity using electric organs made of modified muscle cells called electrocytes, which don’t contract but instead produce electric signals. When activated by the nervous system they produce an electric field.
different types of fish have evolved differently and so location of electric organs differ e,g, some its their tail muscle but not the same for others.
movement of current in the electric discharge organ- CHEAT SHEET
Pacemaker Control
A special area called the pacemaker in the brain generates rhythmic electrical signals.
These signals travel down the spinal cord to motor neurons.
Activation of the Electric Organ
The motor neurons send signals through the peripheral nervous system to the electrocytes (modified muscle or nerve cells in the electric organ).
When an action potential (electrical signal) reaches the electrocytes, they become excited.
Current Flow and Electric Discharge
Electrocytes are stacked in series like batteries. When excited, ions move across their membranes, creating a voltage difference.
Since thousands of electrocytes are aligned, this voltage adds up, generating a current that flows through the entire electric organ.
This produces an electric field around the fish, used for sensing or stunning prey.
Structure of an electric discharge organ?
-Stacks of flattened (muscle) cells
(electrolytes) forming
‘Electroplaques’ or ‘electroplax’.
* An insulating connective sheath surrounds the whole thing.
differences in electric discharge (EOD) in the different types of electric fish
Strongly Electric Fish (e.g., Electric Eels, Electric Catfish)
They have a monopolar discharge, meaning electricity flows in one direction without leaking.
Their entire electric organ is insulated, so all the current is focused on stunning prey effectively.
Weakly Electric Fish (e.g., Knife Fish, Elephant Fish)
Their electric signals are bipolar or more complex, meaning the current flows in two directions or has a wave-like pattern.
These signals aren’t strong enough to stun prey but help with navigation and communication.
how do we measure an electric discharge
-we get a generation of different waves
-we have a tone and the frequency is measured. amplitude can change,. see the lecture slide for different images
evolution of different electric discharge systems
-they change over type
-different diversity in the morphology over time based on different adaptations at the time.
iso-voltage curves (μV)
- what we use to plot the voltage discharge through the environment. voltage diminishes with distance
- can also be used to measure the current flow through the environment
Electroreceptive sense organs
Ampullary receptors:
– Have a jelly-filled opening (canal) through the epidermis to the
outside. Low resistance, and high sensitivity to low frequencies.
– Are found in many fish including weakly electric fish, and in
elasmobranchs (sharks & rays)
* Tuberous receptors:
– Canal loosely ‘plugged’ with
epidermal cells which means:
– 100x less sensitive,
– Only respond to high
frequencies (high-pass filter).
– Are only found in electric fish.
ampullary electroreceptors structure
Dorsal Branch – A nerve pathway that carries electrical signals from the electroreceptors to the brain.
Posterior Lateral Line – A sensory system along the fish’s body that includes electroreceptors, helping detect electric fields in the environment.
Brain – Processes signals from the electroreceptors and controls the electric organ’s discharge.
Electric Organ – Generates electric discharges used for communication, navigation, or stunning prey.
Receptor Areas – Regions in the skin containing electroreceptors that detect changes in electric fields and send signals to the brain= don’t need to know about in details lol
-you can measure the impulse of electric impulses when there is high risk the intensity will be higher polarity can be measures
tuberous electroreceptors
Found only in Gymnotids and Mormyrids, which produce
electric signals.
* Respond to the discharges of electric organs (therefore
respond to high frequency signals).
* Fall into two types:
– Time markers with high sensitivity and fixed latency.
– Amplitude coders with low overall sensitivity but very high
sensitivity to tiny changes in the amplitude of a fish’s own EOD
time markers
Detect the timing of a fish’s own EOD or that of a
conspecific.
amplitude coders
Detect the amplitude of a fish’s own EOD
These receptors together permit:
- Detection of EODs generated by conspecifics – and
thus electrocommunication. - The presence of objects in the environment
– and thus electrolocation.
type of time coders in mormyrids fish: knollenorgane,k receptors
Each organ has 1 to 35 receptor cells, but they all send signals through just one nerve fiber (called a sensory afferent neuron).
→ Many sensors, one output wire to the brain.
Each receptor cell fires only one action potential (nerve signal) for every Electric Organ Discharge (EOD).
→ One zap = one response from each receptor.
The receptor cells are connected to the nerve fiber by electrical synapses, not chemical ones.
→ This makes the signal transfer very fast and accurate (high fidelity).
Types of amplitude codes in mormyrid fish: mormyromasts (amplitude coders,D receptors)
This is the most complex kind of receptor organ.
It has two different types of receptor cells (A and B), and each type is connected to its own nerve fiber.
→ Two kinds of sensors, each with its own wiring.
The organ has extra structural features compared to simpler receptors.
→ More built-in complexity for better processing.
These receptors respond with bursts of spikes (multiple action potentials).
The timing of the first spike tells the brain how strong the signal is:
→ Stronger signal = faster first spike (shorter delay).
→ Weaker signal = slower first spike (longer delay).
time markets in gymnotid fish
Wave Fish
(Wave = they emit continuous wave-like electric signals)
T (Time) receptors
→ Also similar to Knollenorgane
→ Code for precise timing of signals
P (Probability) receptors
→ Like mormyromasts
→ Respond based on how likely a signal is to occur (signal strength = higher probability of response)
how to visualise active electrolocation
- produces an electric image
-see lecture slide as its uper complicated and I too tired to comprehend
how to analyse the information of an electric image
-Different parameters of the ‘electric image’
provide different types of information about the
object:
– The location of receptors detecting a distortion
indicates the location of the object relative to the body.
– The sign of the distortion indicates conductance.
– Changes to the waveform or timing indicate the capacitance.
* Object size, shape and distance –is a complex process that is not yet fully understood in electric fish
ignoring dont thin you will need
can electric fish detect the distance of an object without knowing its size and electrical properties beforehand?
Yes, they can.
How?
Electric fish sense objects using their electric field. When an object enters this field, it alters the electric signal, creating what’s called an electric image.
Far objects = create a large, blurry (low contrast) image
Near objects = create a small, sharp (high contrast) image
what is capacitance and how do fish use capactitance estimation to detect objects
Capacitance = the ability of a material to store electrical charge
Living organisms generally have high capacitance
Inanimate objects generally have low capacitance
Pulse-type electric fish (like mormyrids) emit electric organ discharges (EODs)
They detect objects by analyzing the shape of the returning EOD pulse
High-capacitance objects (like living tissue) cause greater distortion in the EOD pulse
Low-capacitance objects (like rocks or metal) cause less distortion
By comparing pulse shape changes, fish can estimate object capacitance
This helps them distinguish between living and non-living targets in their environment
how do Mormyrid and gymnotid undergo electrocommunication?
~~~
`There are two main types of electric fish based on how they produce signals:
🟠 Pulse-type fish (like Mormyrids)
They send out brief, spaced-out pulses of electricity.
Problem: If many fish are nearby, pulses could overlap, causing interference.
Solution 1: They use sparse signals—meaning, they space them out more so they don’t overlap with others.
Solution 2: They use something called corollary discharge inhibition:
When the fish sends out its own pulse, it temporarily shuts off its own electric receptors (specifically the Knollenorgans).
This prevents the fish from being confused by its own signal.
Think of it like wearing noise-canceling headphones when you talk—you avoid hearing your own voice as a signal.
🔵 Wave-type fish (like Gymnotids)
They produce a continuous electric wave, not pulses.
Each individual fish has a slightly different frequency, typically between 300–600 Hz.
Problem: If two fish have similar frequencies, their waves can interfere with each other (like radio signals crossing).
Solution: They use the Jamming Avoidance Response (JAR):
When two fish get too close in frequency, each fish shifts its own frequency up or down to avoid overlap.
It’s like two radio stations tuning themselves to avoid static.``
