A 2026 research study found that feeding young fish a synthetic male hormone (17α-methyltestosterone) for 60 days caused 73% of genetic females to develop mixed male-female reproductive organs. According to Gram Research analysis, this happened because specific genetic pathways controlling sex hormones and cell survival were activated by the treatment. However, scientists still need to test whether these fish can reproduce normally before this method could be used in fish farming.
Scientists studied what happens when young fish are fed a hormone called 17α-methyltestosterone (MT). According to Gram Research analysis, the hormone caused about 73% of genetic female fish to develop mixed male and female reproductive organs. The researchers looked at which genes turned on and off during this process, discovering that specific genetic pathways related to sex hormones and cell survival were involved. This research could help fish farmers control the sex of farmed fish, though more testing is needed to understand if these fish can reproduce normally.
Key Statistics
A 2026 research article on fish development found that 73% of genetic female fish developed intersex reproductive organs when fed a diet containing 17α-methyltestosterone for 60 days starting at 3 days of age.
Research published in 2026 showed that male-associated genes (cyp11b1, sf1, and dmrt1) increased their activity in hormone-treated fish, while the female-associated gene cyp19a1a decreased, indicating partial genetic sex reversal.
A 2026 study identified that FoxO-related and steroid hormone biosynthesis genetic pathways were significantly enriched in fish undergoing hormone-induced intersex development.
According to 2026 research, hormone-treated intersex fish showed increased male hormone levels and reduced female hormone (17β-estradiol) levels compared to control females, though some female genes remained partially active.
The Quick Take
- What they studied: Whether feeding young fish a synthetic male hormone would change their sex development and which genes were responsible for the changes
- Who participated: Baby fish (Trachinotus blochii) that were 3 days old, fed either a normal diet or a diet containing the hormone for 60 days
- Key finding: The hormone treatment caused 73% of genetic females to develop mixed male-female reproductive organs, with specific male genes turning on and female genes turning off
- What it means for you: This research could help fish farmers produce more male fish for farming, but scientists still need to test whether these fish can reproduce normally before using this method widely
The Research Details
Researchers took baby fish just 3 days old and divided them into two groups. One group ate normal food, while the other group ate food containing 17α-methyltestosterone (MT), a synthetic male hormone, for 60 days. The scientists then examined the fish’s reproductive organs under a microscope and tested their hormone levels in the blood. They also used advanced technology to read which genes were active or inactive in the fish’s reproductive tissues, creating a complete map of genetic activity.
This approach allowed the researchers to see both the physical changes (what the organs looked like) and the genetic changes (which genes turned on and off) happening at the same time. By comparing the treated fish to the untreated fish, they could identify exactly which genetic pathways were involved in the sex change process.
Understanding which genes control sex development in fish is important because it helps scientists figure out how to safely control fish sex in farming. This knowledge could help farmers produce more of the sex they want without harming the fish. The study goes beyond just observing changes—it explains the biological mechanisms behind those changes, which is crucial for developing better methods.
This study examined actual genetic activity in fish tissues, which is more reliable than just observing physical changes. The researchers used established scientific methods to measure both hormones and gene expression. However, the study doesn’t specify exactly how many fish were used, and the researchers note that they still need to test whether these fish can actually reproduce, which is an important limitation.
What the Results Show
When young fish ate food containing the male hormone for 60 days, 73% of the genetic females developed mixed reproductive organs containing both male cells (spermatogonia) and female cells. Blood tests showed that these fish had higher levels of the male hormone and lower levels of the female hormone (estradiol) compared to normal females.
The gene analysis revealed that male-associated genes like cyp11b1, sf1, and dmrt1 became more active in the treated fish, while the female-associated gene cyp19a1a became less active. Interestingly, some female genes like hsd17β1 and foxl2 didn’t completely shut down, suggesting the fish had a mixed genetic state rather than a complete sex change.
The researchers identified two main genetic pathways involved in this process: the FoxO pathway (which controls cell survival and growth) and the steroid hormone biosynthesis pathway (which controls how the body makes sex hormones). Changes in genes related to egg cell development also appeared connected to the hormone-induced changes.
The study found that the hormone treatment didn’t completely erase female characteristics—some female genes remained partially active even in the fish with mixed organs. This suggests that the hormone creates an ‘intersex’ state rather than a complete transformation from female to male. The researchers also noted that multiple genetic pathways were involved, not just one simple on-off switch, indicating that sex development is a complex process controlled by many genes working together.
Previous research has shown that male hormones can influence fish sex development, but this study provides new detail about exactly which genes are involved. The finding that FoxO and steroid hormone pathways are central to this process adds to our understanding of how sex hormones work at the genetic level. This research builds on earlier work by showing the complete genetic picture rather than just the end result.
The researchers didn’t specify the exact number of fish used in the study, making it harder to assess how reliable the results are. The study only looked at what happened during the 60-day treatment period and didn’t follow the fish long-term. Most importantly, the scientists haven’t yet tested whether these intersex fish can actually reproduce or produce healthy offspring, which is essential before this method could be used in fish farming. The study was conducted in one specific fish species, so results may not apply to other fish species.
The Bottom Line
This research is primarily useful for scientists and fish farmers interested in sex control methods. The findings suggest that the FoxO and steroid hormone pathways are key targets for understanding sex development in fish. However, this is early-stage research—scientists should not yet use this method in commercial fish farming without additional testing to ensure the intersex fish are healthy and can reproduce normally. Confidence level: Moderate for understanding the genetic mechanisms; Low for practical application until reproduction is tested.
Fish farmers and aquaculture companies interested in controlling fish sex should follow this research. Scientists studying sex determination in animals will find this valuable. General readers interested in how hormones affect development may find it interesting. People should NOT use this information to attempt hormone treatments on pet fish without veterinary guidance.
The genetic changes happened within the 60-day treatment period in this study. However, long-term effects and reproductive success would take much longer to evaluate—likely several months to years of additional research before this could be considered safe for commercial use.
Frequently Asked Questions
Can you change a fish’s sex with hormones?
Research shows that feeding young fish synthetic male hormones can cause genetic females to develop mixed male-female reproductive organs. A 2026 study found this happened in 73% of treated fish, though scientists still need to test if these fish can reproduce normally before using this method commercially.
What genes control sex development in fish?
Multiple genes work together to control fish sex development. A 2026 study identified that genes like cyp11b1, sf1, dmrt1, and cyp19a1a are key players, along with two major genetic pathways: FoxO and steroid hormone biosynthesis pathways that regulate how sex hormones function.
How long does it take for hormones to change fish sex?
In a 2026 study, genetic changes in fish reproductive organs occurred within 60 days of hormone treatment starting at 3 days of age. However, long-term effects on reproduction and offspring health would require additional months or years of testing before practical application.
Why would fish farmers want to control fish sex?
Fish farmers often prefer one sex over another for farming efficiency and growth rates. Understanding how to control sex development through hormones could help farmers produce more of the desired sex, potentially improving farm productivity and profitability.
Are hormone-treated fish safe to eat?
This 2026 study focused on genetic changes, not food safety. The researchers note that reproduction testing is still needed. Before any hormone-treated fish could be sold for food, extensive safety testing would be required to ensure they’re safe for human consumption.
Want to Apply This Research?
- If tracking aquaculture practices: Monitor the percentage of desired-sex fish produced in each batch and correlate with hormone treatment protocols, recording both the treatment duration and resulting sex ratios weekly
- For aquaculture professionals: Document baseline sex ratios in untreated populations, then implement controlled hormone feeding trials with specific dosages and durations, tracking outcomes systematically before scaling up
- Establish a long-term tracking system that monitors not just initial sex changes but also reproductive success rates, offspring viability, and genetic stability across multiple generations of treated fish populations
This research describes experimental hormone treatment in fish and is intended for educational and scientific purposes. This study has not been validated for commercial aquaculture use. The intersex fish produced in this study have not been tested for reproductive capability or long-term health effects. Anyone considering applying these findings to fish farming should consult with aquaculture specialists and regulatory agencies. This information should not be used to treat pet fish without veterinary guidance. The findings are specific to one fish species (Trachinotus blochii) and may not apply to other species.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.