Glass knifefish

Sensorimotor integration: The Jamming avoidance response of weakly electric fish, Eigenmannia

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What is an electric fish?

Electric fishes: have the ability to generate an electric field---Electrogenic.Knifefish, Torpedo, ElephantnoseElectrogenic are also electroreceptive.

Fishes that are able to detect electric field but are not able to generate an electric field. Electroreceptive : Ability to detect electric field. Sharks, Skates, Rays and Catfish

What is not an electric fish?Apteronotus albifrons

Eigenmannia virescens

Electric fish species can be found both in the sea and in freshwater rivers of South America and Africa.

Electric fishes:(Based on the voltage of EOD)

Weakly electric fish (several hundred millivolts)

Strongly electric fish (several hundred volts)

Electric fishes:(Based on the discharge pattern)Pulse type: Brief electrical pulses followed by

variable intervals of silence.Elephant nose (Gnathonemus petersii)

Wave type: Sinusoidal with duration of electric pulses comparable to duration of interpulse intervals.

Knifefish (Eigenmannia sp)

Electric Organs

Myogenic: Derived from various types of musclesNeurogenic: Derived from modified spinal motor axons(oder Gymnotiformes)

Number of electric organs may be one or more

than one.

Electrocytes are arranged in series. Simultaneous firing of electrocytes results in the electric organ discharges (EODs) which are emitted in the surrounding water.

Composed of electrocytes

The regularity of the electric organ discharge is determined by an endogenous oscillator in medulla oblongata called the pacemaker nucleus (PN).

Electric organ is innervated by electromotoneuronsInnervation site has distinct evagination---stalk

PN

EO

Electromotoneuron

ElectroreceptorsSpecific sensory cell that mediates the perception of electric signal

Senses • own EOD • EOD of other fishes

• Abiotic sources

Electroreceptors are abundant in the head region

Electroreceptors

Ampullary Tuberous

P type (Amplitude) T type (Phase)

Mark Nelson

Electrolocation is the ability of electric fish to detect and localize objects around them. It allows electric fish to hunt and navigate in the absence of visual cues at night or in turbid water.

Conducting object

An object with higher or lower conduc-tivity than the surrounding water causesdistortion of the electric field lines. This causes the area of the skin nearest to the object to have different voltage thanthe rest of the body, which the fish canmonitor by its electroreceptors. Thus, it locates the object.

Electric Current

Electric organElectric organ

Jamming Avoidance Response (JAR)

The most intensively studied behavior of electric fish is the JAR of high frequency wave type species.

The fish’s ability to electrolocate is affected in the presence of another fish with similar EOD frequency. The two electric fields interfere with each other resulting in phase and amplitude modulation of each of the two electric signals. This impairs the fish’s ability to electrolocate.

In order to avoid such detrimental interference of the two electric fields the fish shifts its own frequency away from that of its neighbor.

This behavior is called JAR

What is JAR ?

Eigenmannia virescens

JAR leads to two distinct behavioral patterns

If the neighbor’s EOD frequency is higher than the the fish’s own frequency then the fish lowers its EOD frequency.

If the neighbor’s EOD frequency is lower than the the fish’s own frequency then the fish raises its EOD frequency

BEFORE JARfA=300Hz, fB=304Hz

AFTER JARfA=292Hz, fB=312Hz

DF(frequency difference) = Neighbor(f) – Own(f)Lowers its frequency if DF=(+)ve

Raises its frequency if DF=(-)ve

Frequency shift evoked when DF < 20Hz

Silencing of electric organ with curare.

EOD replaced by electric sine wave of similar amplitude and frequency

Mimic of neighbor’s electric field

Result: Correct jamming avoidance behaviorLowers its pacemaker frequency if DF=(+)veRaises its pacemaker frequency if DF=(-)ve

Do not tell much about the behavioral mechanism involved in determining the sign of DF.

Frequency of the EOD mimic was decreased to a frequency50 Hz below the frequency of the pacemaker nucleus

When confronted with neighbor’s EOD mimic it responded as if this 50 Hz lower frequency was its own frequency.

Pacemaker (f) =100 HzEOD mimic (f)= 50 HzNeighbor’s EOD mimic (f)=54 Hz

Uses the electrical field frequency rather than internal frequency of the pacemaker nucleus----- NO INTERNAL REFERENCE

Fish placed in two compartment chamberPectoral region sealedNo EOD could be detected by head regionJamming stimulus presented to the head

No JAR

JAR elicited when EOD leaked into head chamberJamming signal entered the tail chamber

Fish needs a mixture of its own signal and neighbor’s signal to execute JAR

Electroreceptor

www.trilon.com/electricfish/

A

Mimics of two EODs were added and presented.Electrical fields had differentFrequency, but identical geometryNO VARIATION IN MIXINGRATIO OVER BODY SURFACE----NO JAR

Under natural situationelectrical fields vary both infrequency and geometryVARIATION IN MIXING RATIO-----JAR

The amplitude and the phase of the mixed electric field signalis different from the amplitudes and the phases of the individualsignals. Moreover, the amplitude and phase of the mixed signal aremodulated over the body surface of the electric fish.

By sensing this modulation of the amplitude and phase, the fish candetermine if the other signal has a lower or higher frequency.

Important requirements for JAR:

1. Absolute value of the difference in frequency less than 20 Hz

2. Mixing of signals

3. Variation in mixing ratio

4. Modulation of phase and amplitude of the mixed signal