Animal development begins with an egg fertilization and growth of the one-celled zygote, progressing towards the complex multi-cellular organism. During embryogenesis, many variables, including inherent genetic mutations and environmental stimuli, could impact the developmental outcome. Understanding how a single or combined variation(s) contribute to this process and manipulating them could result in treatments for many developmental diseases. Zebrafish (Danio rerio), as a model organism with over 70% genetic similarity to humans, is used to study genetic mutations and consequential diseases and disorders. With high sensitivity to environmental factors, including water temperature, pH, salinity, DO, pollution, laboratory model zebrafish and natural killifish (Fndulus heteroclitus) populations grant opportunities to investigate numerous genetic and environmental factors and their effects on critical stages of vertebrate development.