The magic of mushrooms: psilocybin influences behavior in the mangrove rivulus fish, Kryptolebias marmoratus

Non-human models, including fish, are increasingly important for investigating how pharmacological agents such as hallucinogens influence behavior, physiology, and cellular processes. These models help to reveal underlying mechanisms and to support assessments of toxicological impact, efficacy, and safety. In this study, we used isogenic lineages of the amphibious mangrove rivulus ( Kryptolebias marmoratus ), an emerging model fish known for high activity and socially dynamic interactions. This species often display aggression towards conspecifics making it well-suited to study behavioral effects of low doses of the psychoactive compound, psilocybin. We determined whether psilocybin could induce calming effects and reduce social aggression and activity. We socially stimulated fish using pairs of size-matched fish from different isogenic lineages and compared baseline social behavior following a waterborne dose of psilocybin. Waterborne psilocybin treatment resulted in a significant decrease in activity levels and in the frequency of swimming bursts (an aggressive behavior) towards a conspecific fish from a different lineage, with modest alterations on other behaviors. Our results also revealed considerable intraspecific variation in the behavioral response of these homozygous fish, suggesting the effects of psilocybin were largely independent of genotype. This study demonstrates that psilocybin reduces aggression and activity in an emerging fish model, adding to the evidence supporting its potential as a therapeutic agent for future clinical translation.