Sex determination is a fundamental process for organisms. There are two mechanisms for sex determination; genotypic sex determination and environmental sex determination. We, human beings, apply the environmental sex determination for the benefits of aquaculture production in some cases, but on the other hand, anthropogenic climate change, global warming, causes the changes of biomass and/or biodiversity which decrease the fishery production in the sea. In this paper, this bilateral character of the effect of heat and temperature on the sex determination in marine organisms is described and provided an explanation.