Warmer temperatures may induce sex change in ricefield eels: new study suggests

Asian swamp eels are on display for sale at a market in the Chinatown neighborhood of the Manhattan borough of New York on Tuesday, Oct. 13, 2020, (AP Photo/Mary Altaffer)

The sex change mechanism in ricefield eels remains a mystery to scientists to this day. However, warmer temperatures may play a role in inducing the sex change, according to a new study from a team of researchers in China.

The study, published in Water Biology and Security, provides new insights into the molecular mechanisms underlying the sex change of this species.

The ricefield eel, also known as the Asian swamp eel, is a freshwater fish originating from areas near India and China but has also been known to be introduced into areas in the U.S., according to the Texas Invasive Species Institute.

These scaleless and finless eels are all born female and transform into males when they mature, due to a process known scientifically as sequential hermaphroditism.

According to researchers, warmer temperatures caused the ovarian tissue to start producing male sex determination genes.

“Temperature-induced up-regulation of male genes depends on Trpv4, a cation channel protein that controls calcium flux into a cell,” said Yuhua Sun, the author said in the study.

Older research revealed that the sex reversing of the ricefield eel is accompanied by changes in the levels of sex hormones and the “expression of sex determination genes.” They found that environmental factors like temperature, light and the potential of hydrogen, or pH, can influence the onset of the sex change.

Sun told CTVNews.ca that some studies have shown a correlation between these factors but adds that experimental data is still lacking.

He said that the eels undergo sex reversal from female to males after around two years, prior to which the females produce eggs.

Sun says the timing of this sex reversal is not synchronized, Sun says, which makes breeding difficult. Basically, the ovary tissues of the females changed to male genes when the temperature is increased from 26 C to 34 C, Sun explained.

If the complexity of the sex reversal -- including the potential role of sex hormones -- could be identified, artificial breeding would be easier and would potentially lead to a lower market price, Sun says.

However, researchers point out that some fundamental questions have still not been answered, like what environmental factor is the most important driver, or how environmental cues are captured and sensed, then converted to the sex determination.