Not all animals retain the sex they had during embryonic development throughout their lives.
For example, some fish, such as clownfish, are initially born as males and then transform into females, remaining so for the rest of their lives. Other species can change sex in the opposite direction, while some possess both male and female reproductive organs, behaving either as males or females at different periods of their lives.
The reasons that prompt fish to change sex can be diverse. For instance, Japanese rice fish, born as genetic males or females, can change their sex in response to fluctuations in water temperature.
Researchers from Nagoya University mention another environmental factor in the journal Biology Open — it turns out that rice fish can become males under conditions of starvation. When females were kept without food for five days, they developed testes, and their fins took on a shape characteristic of males. These changes were observed in only 20% of the females. Subsequent experiments demonstrated that starving fish undergo metabolic changes — they synthesize fewer fatty acids, which, in turn, affects the activity of genes responsible for sex determination.
