Anabas testudineus (Bloch, 1792) is locally known as koi, familiar to people for its exceptional taste. Although koi is listed by IUCN as data deficient, its abundance in natural water bodies of Bangladesh is reduced at a severe scale in comparison to a decade before. Considering the present biodiversity status of A. testudineus in nature, the author conducted this work for conservation of the genetic resources of the fish through cryopreservation of spermatozoa. The book will explain different steps in sperm cryopreservation protocol chronologically which can be applied further in relevant fish species.