Guppy behavior remained abnormal for as long as one week after LSD treatment. From the Science paper that published their discovery,
“The aberrant behavior consisted of periods of normal behavior interspersed at intervals (perhaps every 10-20 minute) with periods of LSD-type behavior.” (Keller,D.L. 1956)The authors reported that reserpine dissolved in the water (20 ug/mL for 3 days) restored normal guppy behavior, but this reserpine-LSD antagonism has not been found in all studies. For example, meal worms fare worse on a reserpine-LSD diet and human beings have reported an unpleasant intensification of LSD effects when combined with reserpine.
The researchers hinted at an underlying problem with their study.
"We have so far been unable to devise a quantitative method for study of the behavior pattern and are therefore limited at the moment to descriptions of its nature." (Keller,D.L. 1956)
KELLER D. L. and W. W. UMBREIT (1956). Chemically altered permanent behavior patterns in fish and their cure by reserpine. Science 124, 407. DOI:10.1126/science.124.3218.407