Cryopreservation is the science in which biological material is preserved at a very low temperature in such a way that germplasms are viable. The germplasm conservation ensures the availability of useful genetic material. Sperm and embryo cryopreservation are important technological tools for ex situ conservation. Sperm of several finfish species has been successfully cryopreserved by developing species-specific protocols. The development of species-specific protocol of cryopreservation is essential, because rapid variations in eco-physiological conditions of fishes have imparted species-specific variations in metabolic pattern of sperm activity during evolution. This book is intended to provide a systematic introduction of cryopreervation of fish sperms/milt which is important technological tools for ex situ conservation of declining populations of fishes.