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← Theoretical A

Q42 — Electric Eel Prey Detection

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Foraging & Anti-Predator Behavior

Electric eels (Electrophorus electricus) are predatory fish that utilize electrical and mechanical signals during hunting. They emit two types of electrical impulses: low-voltage, which induces sudden muscle contraction of the prey, and high-voltage, which paralyzes the prey, aiding in capture and consumption.

In the experiment conducted for studying electrolocation mechanisms of eels, a container with two compartments was used, as shown in Figure 1. The lower compartment contained an isolated fresh fish corpse attached to electrodes, connecting it to the upper compartment’s environment. Additionally, several electrically non-conductive rods and one conductive rod were placed beneath the transparent, perforated divider.

Results of the experiment indicated that upon placement in the container, the eel began attacking the conductive rod, but not the fish corpse (Figure 2). Assume that the fish corpse was supplied with a sufficient amount of ATP.

Diagram of the experimental setup: a two-compartment container with the eel in the upper compartment above a transparent perforated divider, electrodes connecting to an isolated fish corpse below, and conductive and non-conductive rods placed near the corpse. Figure 1. Experiment setup; black arrow - conductive rod.

Recorded low- and high-voltage electrical impulses from the eel over time, alongside video frames from bottom and side views showing the eel attacking the conductive rod. Figure 2. A Impulses recorded from the upper compartment (x-axis - time, y-axis - voltage); LW - low voltage impulse, HW - high voltage impulse. B Frames shot from the experiment (BV - bottom view, SV - side view); black arrow - conductive rod, red arrow - attack. The fish corpse is highlighted in red.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Only low-voltage impulses are required for prey electrolocation.
B. The divider blocked the movement of water between the compartments.
C. The first frame in Figure 2B was taken before the corpse began to contract.
D. Eels prefer to rely on their mechanoreceptors rather than electroreceptors when localizing the exact location of their prey.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)