The previous chapters have summarized, reviewed, and presented published and original data on the work being done across various disciplines to understand the overall biology and evolution of annual shes. The term “annual shes” was coined to apply to sh species living in temporary freshwater biotopes, which dry seasonally (Myers, 1952). This term also describes the atypical, among vertebrates, short lifespan of this group of shes that would have evolved as an adaptation to inhabit ephemeral pools of water that vanish during the dry season. Adults of Neotropical annual shes usually live in temporal ponds less than 1 year (e.g., Austrolebias), whereas in some species of African annual shes lifespan may be as low as 17 weeks (e.g., Nothobranchius furzeri). The annual condition was described by two characteristics: (1) a unique stage during early development, the dispersion-reaggregation of deep blastomeres that separates epiboly to embryonic axis formation, and (2) the possibility of the embryo to enter in developmental arrests or diapauses before hatching (Myers, 1952; Wourms, 1972a,b,c).