Scotophobin (from ancient Greek σκότος skótos "darkness" and φόβος phóbos "fear") is a peptide  discovered by neuroscientist Georges Ungar in 1965 and reported in 1968. The results of Ungar and his collaborators seemed to show that scotophobin induces fear of the dark in various mammals and fish. It was discovered  in the brain of laboratory rats  conditioned to have a fear of darkness. Moreover, it was claimed that its injection could transfer fear to unconditioned rats.  It was the core argument for the hypothesis about memory transfer: that memories are molecularly stored in the brain. Chemical memory transfer was a subject of conferences and books. According to the current knowledge, scotophobin cannot have the effect attributed to it.
The history of scotophobin is covered in the 2006 book Scotophobin: Darkness at the Dawn of the Search for Memory Molecules, a personal account of Louis Neal Irwin, who participated in this research.