To investigate this question, Canadian researchers examined how psilocybin affected mangrove rivulus fish (Kryptolebias marmoratus), an amphibious species known for aggressive social behavior. Their findings, published in Frontiers in Behavioral Neuroscience, suggest that even brief exposure to a low dose of psilocybin can reduce aggressive behavior without eliminating normal social interactions.

“We showed that acute, low-dose psilocybin significantly reduced activity and aggressive behavior during social interactions in adult mangrove rivulus, a naturally highly aggressive species,” said lead author Dana Forsyth, a researcher and former master’s 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 interactions,” added co-lead author Dr. Susie Currie, a biologist at the University of British Columbia.

Why Scientists Studied Aggressive Mangrove Rivulus Fish

Mangrove rivulus fish are naturally aggressive, particularly when they encounter members of their own species. Their aggressive responses are easy to observe and measure, allowing researchers to detect relatively small changes in behavior.

The fish also have unusual reproductive abilities. They can fertilize themselves and produce genetically identical offspring. This makes them useful for experiments because researchers can minimize genetic variation and have greater confidence that behavioral differences are related to psilocybin rather than inherited traits.

For the experiment, the researchers used three genetically distinct strains of fish raised in the laboratory. One group received psilocybin, another included stimulus fish to trigger social interactions, and a third group helped researchers measure how much psilocybin entered the animals’ bodies and accumulated.

The researchers first established each fish’s behavioral baseline. They placed a fish in a tank containing another fish, separating them with a fiberglass mesh barrier and an opaque cover. The mesh prevented physical contact while allowing the fish to see and smell each other once the cover was removed.

After five minutes, the fish had become accustomed to their shared environment. The researchers then removed the opaque cover and recorded their interactions.

The following day, 24 hours after the initial observation, the same fish were placed in water containing dissolved psilocybin. After 20 minutes of exposure, they were returned to an aquarium containing the fish they had previously encountered. The researchers removed the cover again and recorded any changes in behavior.

Low-Dose Psilocybin Reduced Aggressive Attacks

The results showed notable behavioral changes. Fish exposed to psilocybin moved less and displayed fewer aggressive swimming behaviors than fish that did not receive the compound.

To measure these changes, the scientists recorded overall activity, including the amount of time the fish spent swimming, as well as several signs of aggression. These included rapid bursts of swimming, which can indicate that an interaction is escalating toward an attack even when the fish cannot make physical contact.

“Swimming bursts are high-energy aggressive behaviors that represent an escalation of aggression toward a stimulus fish without physical contact,” Currie explained. “Other types of aggressive behavior, such as head-on displays, are focused on communication and social evaluation and require little energy.”

Psilocybin did not suppress every form of aggressive or social behavior. Treated fish were less likely to engage in vigorous, energy-intensive attacks, while their less physically demanding social displays remained largely unchanged.

“The sedative effects of psilocybin appear to selectively reduce energetically costly escalating behaviors, while low-energy social display behaviors remain largely unchanged,” Forsyth said. “This suggests that this compound can selectively attenuate escalating social conflict rather than completely silencing the behavior.”

The compound also reduced general activity. When placed alongside other fish of the same species, psilocybin-treated fish spent less time swimming than untreated control fish.

Taken together, the findings suggest that psilocybin may affect specific aspects of aggressive behavior rather than simply making the animals less responsive to their surroundings.

What the Findings Mean for Psychedelic Research

The researchers believe animal studies such as this one could help scientists better understand how psychedelic compounds influence behavior and identify possible directions for future therapeutic research.

By examining which social responses are most sensitive to psilocybin, researchers may be able to investigate biological mechanisms that are difficult to study directly in humans. These findings could eventually inform research into potential clinical applications.

However, the researchers emphasized that the study does not show that psilocybin can treat aggression in humans. The experiment involved fish, and no clinical intervention was evaluated. It is therefore impossible to determine whether similar effects would occur in people.

Important questions also remain about how long the behavioral changes last. The researchers examined only a single dose and a short exposure period. They did not study repeated treatments, long-term behavioral changes, or whether the fish adapted to psilocybin over time.

Additional experiments are needed to determine whether psilocybin’s ability to reduce escalating aggression can continue beyond the short period examined in this study.

“Future research could build on this work to explore how psilocybin alters neural signaling, which serotonin pathways are involved, and why some aspects of social behavior are affected while others are not,” Currie concluded. “These are questions that are difficult or impossible for humans to answer directly.”