The fish that help each other sense the world

Many animals rely on self-generated signals to take in the world around them. Bats and dolphins, for example, emit auditory signals and analyze the reflections, similar to sonar. Some fish emit and interpret electric signals.

But get enough members of an actively sensing species together and interference can become an issue. Fish that emit electricity continuously have been observed changing the frequency of their emissions to avoid cross talk. Researchers had assumed that fish that emit their signals in pulses must also contend with jamming. But a new study suggests the opposite: Some electricity-emitting fish may benefit from the presence of other fish of the same species.

Federico Pedraja and Nathaniel Sawtell of Columbia University’s Zuckerman Institute studied Gnathonemus petersii, commonly known as the African elephantnose fish, which emits an electric pulse from its tail that eventually returns and induces a current on the fish’s skin. The researchers mapped the electric currents by recording the fish’s brain activity. Using methods laid out in previous work, they created a correlation map between the electric field potentials in regions of the brain and the presence of currents on different areas of the skin. That showed Pedraja and Sawtell a simplified version of the electric image that the fish experience. They also used simple 3D models built from basic electricity-physics principles.

With multiple signals being processed by the fish in quick succession, the researchers classified the electric images by whether they are a self-image, generated by a signal from the same fish that is receiving it, or a cons-image, one based on a pulse from another fish. They found that not only does a fish use cons-images to gather information about the environment, but those images can also lead to improved sensitivity and a greater sensing range.

Pedraja and Sawtell modeled eight arrangements of fish and target objects. One advantageous positioning is two fish with their bodies perpendicular to each other and the object of interest near one of them. The farther fish might not sense the object through a self-image, but it benefits from the cons-image signal, which travels directly from the fish near the object, through the object, and to the farther fish. Although not every arrangement of fish increases their sensing range, additional signals can still help them differentiate an object from noise.

The researchers cannot say for sure whether the fish seek out others to enhance their perception, but the fish’s behavior suggests that they are aware of the benefit. Pedraja, Sawtell, and other researchers have observed the fish swimming to be near each other at night when their vision is worse. Such a strategy might help the elephantnose fish avoid predators. (F. Pedraja, N. Sawtell, Nature, 2024, doi:10.1038/s41586-024-07157-x .)