Psilocybin Reduces Aggression in Fish: Groundbreaking Study Reveals Behavioral Shift

Move over, coked-up salmon. A groundbreaking study has revealed that psilocybin—the psychoactive compound found in magic mushrooms—reduces aggression in fish, according to research published on Thursday, June 13, 2024, in Frontiers in Behavioral Neuroscience.

Scientists have long studied psilocybin’s effects on humans and mammals, but fish offer unique advantages due to their diverse social structures and activity levels. This study is the first to demonstrate that psilocybin reduces aggression in any animal model, opening new avenues for research into the neural mechanisms behind these behavioral changes.

Why Mangrove Rivulus Fish? A Model for Behavioral Studies

The research focused on the mangrove rivulus fish (Kryptolebias marmoratus), a highly aggressive species with remarkable adaptations. These fish can survive out of water for months and are rare hermaphroditic species that reproduce through self-fertilization, producing genetically identical clones. This eliminates genetic variation as a factor in experiments.

“Each lineage that we have is essentially genetically identical, and between lineages, they are genetically distinct. So, we eliminate the genetic factor, and just focus on the behavioral effect.”

Dayna Forsyth, research associate at Acadia University in Nova Scotia and lead author of the study, explained in an interview with 404 Media.

The Experiment: Tracking Behavioral Changes

To test psilocybin’s effects, Forsyth and her team placed two undosed fish on opposite sides of a tank, separated by a mesh barrier that allowed visual and olfactory interaction but prevented physical contact. The “focal fish” was then removed, exposed to a low dose of psilocybin for 20 minutes, and returned to the partitioned tank to observe its behavior toward the undosed “stimulus fish.”

“We really had no idea what we were getting ourselves into. We didn't have much to go off of before. My research question throughout was just: ‘does psilocybin affect fish behavior?’ We had no idea when we first started this, because there weren't too many papers out there on fish.”

As it turned out, psilocybin had a noticeable impact. Mangrove rivulus fish typically express aggression through sudden, high-energy darting bursts. However, the dosed fish exhibited significantly fewer of these aggressive charges. Surprisingly, they still engaged in less overtly hostile behaviors, such as lateral and head-on displays used to assess peers.

“We definitely predicted that all aggressive behaviors, including those lateral and head-on displays, would be decreased. We really did not expect it to just target that highly aggressive and more energetically costly behavior, rather than the low-energy behaviors. That was definitely a surprise.”

Dayna Forsyth

Implications and Future Research

This study adds to a growing body of research on psilocybin’s therapeutic potential, particularly in modulating behavior. While the findings are preliminary, they suggest that psilocybin could influence neural pathways related to aggression across species. Researchers are now exploring whether similar effects occur in other animals, including mammals.

The study also highlights the importance of studying aquatic ecosystems, where drug pollution—such as cocaine exposure in salmon—has already raised concerns about behavioral and ecological impacts.