Mechanisms of the animal reproductive development are an important research field in life sciences. The study of the reproductive development and regulatory mechanisms in fishes is important for elucidating the mechanisms of animal reproduction. This paper summarizes recent advances in the mechanisms of fish sex determination and differentiation, of fish gonad development and maturation, and of fish germ cell development, as well as the according regulating strategies. Fishes comprise an evolutionary stage that links invertebrates and higher vertebrates. They include diversiform species, and almost all vertebrate types of reproduction have been found in fishes. All these will lead to important advances in the regulatory mechanisms of animal reproduction by using fishes as model organisms. It will also enable novel fish breeding techniques when new controllable on-off strategies of reproduction and/or sex in fishes have been developed.