Leo Margolis, OC FRSC (December 18, 1927 – January 13, 1997) was a Canadian parasitologist. He was a pioneer in the use of parasites for identification of Pacific Ocean fish stocks. His discoveries became a crucial point in negotiations over pacific salmon fisheries, as it could now be determined where each individual fish spawned, in the rivers of Canada or the United States.Born in Montreal, Quebec, he received a B.Sc. in 1948, a M.Sc. in 1950, and a Ph.D in 1952 from McGill University.