Francis Talbot Day CIE (2 March 1829 – 10 July 1889) was an army surgeon and naturalist in the Madras Presidency who later became the Inspector-General of Fisheries in India and Burma. A pioneer ichthyologist, he described more than three hundred fishes in the two-volume work on The Fishes of India. He also wrote the fish volumes of the Fauna of British India series. He was also responsible for the introduction of trout into the Nilgiri hills, for which he received a medal from the French Societe d'Acclimatation. Many of his fish specimens are distributed across museums with only a small fraction deposited in the British Museum (Natural History Museum, London), an anomaly caused by a prolonged conflict with Albert Günther, the keeper of zoology there.