Genetic Variability in Natural Populations of Fishes

Intraspecific variation encompasses variability at the genetic as well as phenotypic level and is found within and among populations. The documentation of below-species-level (intraspecific) variations is important for conservation and management. The FAO’s Commission on Genetic Resources for Food and Agriculture (CGRFA) has underscored the significance of biodiversity conservation for posterity. Advancements in molecular markers have enabled the delineation of genetic diversity (intra-and interspecific), which has applications in stock characterization, parentage assignment, and genetic rescue/stock enhancement programs. This chapter highlights the importance and need for revealing intraspecific genetic variations, their quantification, and neutral as well as adaptive divergence. Evolutionary forces that shape the patterns of genetic diversity are also described. Threats emanating from various anthropogenic causes, especially loss of natural genetic diversity due to the unintended mixing of farm-bred stock are worth mentioning in the current scenario. The genetic information, below-species-level plays a significant role in resource management, registration of genetic stocks and the elite germplasm.