text: Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. It is observed in reptiles and teleost fish, with some reports of it occurring in species of shrimp. TSD differs from the chromosomal sex-determination systems common among vertebrates. It is the most studied type of environmental sex determination (ESD). Some other conditions, e.g. density, pH, and environmental background color, are also observed to alter sex ratio, which could be classified either as temperature-dependent sex determination or temperature-dependent sex differentiation, depending on the involved mechanisms. As sex-determining mechanisms, TSD and genetic sex determination (GSD) should be considered in an equivalent manner, which can lead  to reconsidering the status of fish species that are claimed to have TSD when submitted to extreme temperatures instead of the temperature experienced during development in the wild, since changes in sex ratio with temperature variation are ecologically and evolutionally relevant.
  While TSD has been observed in many reptile and fish species, the genetic differences between sexes and molecular mechanisms of TSD have not been determined. The cortisol-mediated pathway and epigenetic regulatory pathway are thought to be the potential mechanisms involved in TSD.
  The eggs are affected by the temperature at which they are incubated during the middle third of embryonic development. This critical period of incubation is known as the thermosensitive period. The specific time of sex-commitment is known due to several authors resolving histological chronology of sex differentiation in the gonads of turtles with TSD.