Monday, August 11, 2014

Methysergide fish surfacing reaction

Methysergide, also referred to as UML-491, causes the fish surfacing reaction in the same way that LSD does, but a higher dose is needed. In goldfish, methysergide is about 250X less potent than LSD at eliciting the reaction. The figure below shows the fish surfacing curve for methysergide. A concentration of 50 ug/mL of UML-491 in the outside liquid gave approximately the same per cent of goldfish reacting as 0.2 ug/mL LSD.

Methysergide is considered to be a hallucinogenic drug in humans. Just as a larger dose of methysergide is needed to elicit the fish surfacing reaction, a larger dose of methysergide is needed for human effect.

The LSD-like fish surfacing reaction is also observed for MLD-41, which is similar in its structure to LSD, the only difference being that MLD-41 contains one methyl group more than LSD.


Gettner H. H., A. Rolo and H. A. Abramson (1965). Lysergic acid diethylamide (LSD 25). 36. comparison of effect of methysergide (UML 491) on goldfish and siamese fighting fish. The Journal of Psychology 61, 87-92.