A11 Electroreception Disruption

Topic

The fish's biogenic electric field is central to this model: it is the specific electrical signal generated by the fish, which its electroreceptors use for orientation and environmental sensing. Disruption of electroreception occurs when artificial electric fields present in the water mask or distort this biogenic field, preventing the fish's electroreceptors from functioning normally. These artificial electric fields originate from diverse sources: stray currents from aquaculture facilities, underwater high-voltage power lines, electrofishing, submarine communication cables, and vessel electrodes. Active electroreceptive fish—known as weakly electric fish—are particularly vulnerable to this electrical pollution because their electroreceptors detect extremely faint electric fields, as weak as one nanovolt per centimeter.

This electrical pollution overlays the fish's biogenic electric field in the same way background noise overlays a signal one wishes to detect. If the strength of the external electric field—concentrated within the same frequency range as the fish's own electric organ discharge—exceeds the fish's detection threshold, the fish completely loses the ability to electrolocate its surroundings. The severity of this disruption can be summarized by a masking index, which compares the strength of the external electric field to that of the fish's own biogenic field at its typical electrolocation range: the higher the index, the more the fish's biogenic field is masked and the less capable the fish is of electrolocating. Alternating current flowing through the electrical grid—with a frequency of fifty or sixty hertz, depending on the region—is particularly disruptive to freshwater fish whose electric organ discharges operate at similar frequencies; this is because the external field falls squarely within the frequency range to which the fish is most sensitive. Electrofishing deliberately exploits this very vulnerability: currents ranging from fifty to three hundred volts per meter applied to river water first induce galvanotaxis—causing the fish to orient itself and swim toward the positive electrode—and, at higher intensities, trigger galvanonarcosis, or complete immobilization. Both effects depend on the amount of electric current that actually passes through the fish's tissues.

Beyond acute events like electrofishing, chronic exposure to electrical pollution also leaves a measurable mark on the fish: it raises the fish's electrolocation threshold in proportion to the ratio between the external field and the biogenic field (described earlier), and reduces its success in hunting prey that requires electrolocation for detection. This reduced hunting success ultimately affects the fish's nutritional status and physical condition; thus, when the biogenic electric field—the very field described at the start of this model as the foundation of the fish's electrosensory system—is persistently masked, it ultimately compromises the fish's ability to feed.

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