He took a special interest in seasonal phenomena and is considered as a founder of phenology studies in Austria.
After school he studied philosophy and law (1833–1836) and during his internship he met Karl Kreisl at the Prague Observatory who supported him.
When the Central Institute for Meteorological and Earth Magnetism was established in Vienna in 1851, Fritsch joined as an adjunct.
He established a network of observers who provided him data on the first appearance of bees in spring, the flowering of plants, as well as other seasonal phenomena.
He presented the work on the long term studies on periodical phenomena in animals and plants at the London Statistical Congress of July 1860.