Hallucinogenic Fish

Sarpa salpa (above) is a type of sea bream found in the Mediterranean as well as in temperate areas of the Indian and Pacific Oceans. It has one unusual quality. Eating it can cause hallucinations. For this reason, it's sometimes called the "dreamfish."
People have known about this for a long time. Apparently Sarpa salpa was occasionally eaten for recreational purposes during the Roman Empire.
A 2006 article in the journal Clinical Toxicology describes some medical case reports involving dreamfish consumption. For instance, in 1994 a 40-year-old man on vacation in the French Riviera ate some, and the next day the hallucinations began:

he began to experience blurring of vision and hallucinations involving aggressive and screaming animals. Agitation and disorientation led him to seek medical assistance (he was not able to drive anymore as he was seeing giant arthropods around his car). Physical examination upon arrival at the hospital emergency room demonstrated no notable abnormalities: no fever, no sign of focalization or sensory-motor deficit, and normal hemodynamic status except for sinusal tachycardia linked directly to the mental disturbances. During hospitalization, the patient recovered rapidly with complete resolution of symptoms within 36 h post ingestion. He was unable to recall the hallucinatory period.

Similarly, in 2002 a 90-year-old retiree ate some sea bream, again in the French Riviera, and experienced hallucinations involving "human screams and bird squealing."
A case described on Wikipedia seems to have been far more pleasurable. In 1960, National Geographic photographer Joe Roberts purposefully ate some broiled dreamfish: "he experienced intense hallucinations with a science-fiction theme that included futuristic vehicles, images of space exploration, and monuments marking humanity's first trips into space."
The authors of the Clinical Toxicology article note that cases of hallucinogenic fish poisoning (ichthyoallyeinotoxism) are often confused with ciguatera poisoning — the latter caused by fish flesh contaminated by "various toxins produced by the benthic dinoflagellate Gambierdiscus toxicus."
Ciguatera can also cause hallucinations. However, it may also kill you, whereas you should recover from the dreamfish hallucinations within 36 hours.