Scientists Used Psilocybin To Calm One of Nature’s Meanest Fish
Psilocybin reduced aggressive attacks in territorial fish while preserving normal social behavior.
Even the most naturally aggressive fish can find a sense of calm when exposed to the compounds found in magic mushrooms.
Researchers from Acadia University and The University of British Columbia recently tested these effects on the mangrove rivulus fish. The study found that low doses of psilocybin reduced high-energy attacks while leaving normal social interactions intact.
The role of psilocybin in social behavior research
Psilocybin, found in over 200 species of magic mushrooms, is gaining traction in clinical research for its ability to bind to serotonin receptors and influence mood.
While its effects on individual human psychology are well documented, science still knows very little about how it influences the way animals interact in social groups.
To understand this, researchers are turning to a unique model: the mangrove rivulus (Kryptolebias marmoratus). This amphibious fish is a self-fertilizing hermaphrodite that produces genetically identical offspring.
These fish are also notoriously aggressive; they are territorial and react strongly when paired with others, making them perfect for testing anti-aggression treatments. The new study aimed to determine if an acute, low dose of psilocybin could selectively reduce social aggression and activity in a highly territorial vertebrate without causing total sedation.
How psilocybin selectively reduces social aggression
The team used three genetically distinct laboratory lines for the study: DAN, PAN, and HON. To deliver the treatment, they immersed each fish in a water bath containing 5 μg/L of psilocybin for 20 minutes.
Before the treatment, the researchers established a baseline for each focal fish by placing it in a tank with a stimulus fish. A focal fish refers to the specific individual being treated and observed, while the stimulus fish was used to prompt a social reaction.
A mesh barrier allowed them to see and smell each other without physical contact. This setup ensured the researchers could quantify the natural levels of aggression before any intervention took place. The barrier was then removed after the adjustment period.
Aggression was measured through two distinct behaviors: swimming bursts and head-on displays.
“Swimming bursts are high‑energy attack behaviors that represent an escalation of aggression towards the stimulus fish without making physical contact,” explained senior author Dr. Suzie Currie, the vice principal and associate vice president of research and innovation and a professor of biology at the University of British Columbia. “Other types of aggressive behaviors, like head‑on displays, are more about communication and social assessment and require very little energy.”
After exposure to psilocybin, the fish spent significantly less time moving and performed far fewer of these high-energy bursts when in the tank with a stimulus fish.
“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 at Acadia University.
However, psilocybin did not shut down all activity; while the fish became more mellow, they remained socially engaged.
“Psilocybin’s calming effect appears to selectively reduce energetically costly, escalated behaviors while lower‑energy social display behaviors remained largely unchanged,” said Forsyth. “This suggests that this compound can selectively dampen escalated social conflict rather than shutting down behavior altogether.”
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Clinical implications and future psilocybin studies
By targeting high-energy conflict without suppressing basic social interaction or communication, psilocybin offers a nuanced way to manage behavior. This has potential implications for human therapy, where researchers are looking for ways to treat pathological aggression without the sedation often associated with traditional medications.
The fact that psilocybin works this way in a fish also points to the deeply conserved nature of serotonin pathways across the animal kingdom, from aquatic life to mammals.
However, the researchers are careful to note the study's constraints. The experiment used only a single, acute dose and did not track long-term adaptation or the effects of repeated exposure. There is also the inherent challenge of translating results from a 3 cm fish to a human patient.
The study did confirm that psilocybin was present in both the brain and body tissues, but more work is needed on the specific pharmacokinetics involved.
“Future studies can 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,” concluded Currie. “These are questions that are difficult or impossible to answer directly in humans.”
Reference: Forsyth D, Faraone N, Lamarre SG, Currie S. The magic of mushrooms: psilocybin influences behavior in the mangrove rivulus fish, Kryptolebias marmoratus. Front Behav Neurosci. 2026;20:1767175. doi: 10.3389/fnbeh.2026.1767175
This article is a rework of a press release issued by Frontiers. Material has been edited for length and content.
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