21. The elephant-nosed weakly electric fish generate electric fields to locate and identify
nearby objects. They detect distortion of their own electric organ discharge to identify
nearby objects. Consider the two following statements:
i. An object is detectable if its specific resistance is different from that of water
ii. An object is detectable if its specific capacitance is different from that of water
a. Both statements i and ii are true.
b. Only statement i is true.
c. Only statement ii is true.
d. Neither statement i nor statement ii are true.
Elephant-Nosed Fish Electrolocation: Both Statements i and ii are True (Option a).
Elephant-nosed weakly electric fish, such as Gnathonemus petersii, generate electric organ discharges (EODs) that create a self-generated electric field around their body. Nearby objects distort this field, and specialized electroreceptors (mormyromasts) detect changes in local EOD amplitude and waveform, enabling active electrolocation. Low-resistance (conductive) objects increase local EOD amplitude compared to water, while insulators (high resistance) decrease it; capacitive objects further distort the waveform beyond pure resistance effects.
Option Analysis
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Option a (Both true): Correct, as objects differing in specific resistance alter EOD amplitude, and those differing in specific capacitance modulate both amplitude and waveform, making them detectable. Fish discriminate resistive vs. capacitive properties via these perturbations.
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Option b (Only i true): Incorrect, ignores capacitance detection shown in behavioral and neural studies.
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Option c (Only ii true): Incorrect, as resistance differences alone suffice for detection via amplitude changes.
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Option d (Neither true): Incorrect, as both properties contrast with water’s baseline impedance for reliable object identification.
Introduction
Elephant-nosed fish electrolocation relies on detecting electric field distortions caused by objects with specific resistance or capacitance differing from water, enabling precise object identification in murky environments. This mechanism, key for CSIR NET Life Sciences, involves self-generated electric organ discharges (EODs) sensed by electroreceptors.
