Psilocybin, the psychedelic substance found in more than 200 species of mushrooms, appears to have an unexpected effect on aggressive fish. Most mushrooms containing this compound belong to the gilled mushroom genus Psilocybe. In mammals, psilocybin interacts with serotonin receptors in the brain, influencing emotions and behaviors such as mood, appetite, and aggression.
However, scientists still know relatively little about how the substance affects social interactions among animals. To investigate this question, researchers in Canada examined the effects of psilocybin on the amphibious mangrove rivulus fish (Kryptolebias marmoratus). Their findings, published in Frontiers in Behavioral Neuroscience, suggest that even a brief exposure to a low dose can significantly reduce aggressive behavior without disrupting normal social interactions.
"We show that an acute, low dose of psilocybin significantly reduces activity and aggressive attack behavior during social interactions in adult mangrove rivulus fish, a species that is naturally highly aggressive," said first author Dayna Forsyth, a research associate and former MSc student at Acadia University in Nova Scotia. "These findings provide the first evidence that psilocybin can selectively reduce escalated aggression in a vertebrate model without suppressing social interaction," added senior author Dr. Suzie Currie, a biologist at The University of British Columbia.
Why Scientists Studied Aggressive Mangrove Rivulus Fish Mangrove rivulus fish are naturally combative, particularly when they encounter another member of their species. Their aggressive responses are easy to recognize and measure, allowing researchers to detect even small changes in behavior. These fish also have an unusual reproductive ability.
They can fertilize themselves, producing offspring that are genetically identical. This makes them especially useful for experiments because scientists can minimize genetic variation and more confidently attribute behavioral differences to psilocybin rather than inherited traits. For the experiment, the researchers worked with three genetically distinct lines of fish bred in the laboratory.
One group received psilocybin, another provided the fish used to provoke social interactions, and the third helped researchers measure how much psilocybin entered and accumulated in the animals' bodies. The researchers first established a baseline for each fish's behavior. They placed a fish into a tank already occupied by another fish, with the two separated by a fiberglass mesh barrier and an opaque cover.
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