Know more

Our use of cookies

Cookies are a set of data stored on a user’s device when the user browses a web site. The data is in a file containing an ID number, the name of the server which deposited it and, in some cases, an expiry date. We use cookies to record information about your visit, language of preference, and other parameters on the site in order to optimise your next visit and make the site even more useful to you.

To improve your experience, we use cookies to store certain browsing information and provide secure navigation, and to collect statistics with a view to improve the site’s features. For a complete list of the cookies we use, download “Ghostery”, a free plug-in for browsers which can detect, and, in some cases, block cookies.

Ghostery is available here for free:

You can also visit the CNIL web site for instructions on how to configure your browser to manage cookie storage on your device.

In the case of third-party advertising cookies, you can also visit the following site:, offered by digital advertising professionals within the European Digital Advertising Alliance (EDAA). From the site, you can deny or accept the cookies used by advertising professionals who are members.

It is also possible to block certain third-party cookies directly via publishers:

Cookie type

Means of blocking

Analytical and performance cookies

Google Analytics

Targeted advertising cookies


The following types of cookies may be used on our websites:

Mandatory cookies

Functional cookies

Social media and advertising cookies

These cookies are needed to ensure the proper functioning of the site and cannot be disabled. They help ensure a secure connection and the basic availability of our website.

These cookies allow us to analyse site use in order to measure and optimise performance. They allow us to store your sign-in information and display the different components of our website in a more coherent way.

These cookies are used by advertising agencies such as Google and by social media sites such as LinkedIn and Facebook. Among other things, they allow pages to be shared on social media, the posting of comments, and the publication (on our site or elsewhere) of ads that reflect your centres of interest.

Our EZPublish content management system (CMS) uses CAS and PHP session cookies and the New Relic cookie for monitoring purposes (IP, response times).

These cookies are deleted at the end of the browsing session (when you log off or close your browser window)

Our EZPublish content management system (CMS) uses the XiTi cookie to measure traffic. Our service provider is AT Internet. This company stores data (IPs, date and time of access, length of the visit and pages viewed) for six months.

Our EZPublish content management system (CMS) does not use this type of cookie.

For more information about the cookies we use, contact INRA’s Data Protection Officer by email at or by post at:

24, chemin de Borde Rouge –Auzeville – CS52627
31326 Castanet Tolosan CEDEX - France

Dernière mise à jour : Mai 2018


Home page


2016 - 2020 (47 months) Rainbow trout (Oncorhynchus mykiss)

sex differencation and genetic bases for temperature-controlled sex control of trout breeders

Scientific objectives :

  • Test in rainbow trout the possibility of exploiting hot heat treatments (18°C) as an alternative to hormonal treatments to obtain neomales for the production of female monosex populations,
  • To specify the conditions for the implementation of this thermal method of sexual inversion in the long-term management of rainbow trout stocks.

Roles of SYSAAF :

  • Involved in the definition of the experimental scheme
  • Sampling organisation at national level, from diploid and triploid populations
  • Analyses of the genetic origins of spontaneous neomales
  • Dissemination of the results and technical know-how to the French producers of rainbow trout

Program completed October 31st, 2020

NeoBio Project Briefing Note

The production of rainbow trout is mainly based on the production of female monosex herds. However, the presence of undesirable male animals in monosex populations is reported on a recurring basis. The NeoBio project explored the genetic and zootechnical bases of this spontaneous masculinization, with a double objective:

propose methods for controlling the phenomenon,

and possibly, to exploit it to develop an alternative method of production of neomales by application of an early heat treatment that would benefit the production of organic trout.

INRAE, SYSAAF and a private fish farm (Les fils de Charles Murgat) worked together to :

  • sample different French populations and a precise description of the phenomenon,
  • validate the effect of early heat treatment on the frequency of spontaneous masculinization,
  • specify the genetic basis for masculinization sensitivity and identify genetic markers associated with this trait.

The lessons of this joint work are :

- spontaneous masculinization is a phenomenon observed in different trout populations, at generally limited frequencies (of the order of one percent). Some individuals are only partially affected (intersex). Genetic controls confirm that totally or partially masculinized animals are indeed genetic females.

- the frequency of masculinized individuals depends on the thermal regime received by the fry during the early stages (from hatching to a few weeks of feeding). In the study population, depending on when it is applied, the same high temperature (18°C) was associated with a reduction or increase in the frequency of masculinized animals compared to the alevinated control lot at a lower standard temperature (approximately 12°C).

- spontaneous masculinization has a complex genetic basis, independent of the major sex determinant carried by sex chromosomes (XX- XY). It’s a very inheritable character. By combining medium-density (30,000 SNP markers) genotyping of male or female individuals, and complete genomic sequencing of their mothers, it was possible to identify several genomic zones associated with masculinization, including one zone on chromosome 1, carrier of few mutations present preferentially in masculinized individuals (males and intersex). Within this region, several candidate genes potentially involved in spontaneous masculinization have been identified. Although this area of chromosome 1 appears to play a major role in several populations, it is not systematically found, and different zones have been identified according to populations, illustrating the complexity of the underlying genetic determinism.

These results show that spontaneous masculinization in female trout is controlled by both environmental factors (rearing temperature) and genetic factors that coexist with the major sex determinant. They are a first step towards understanding the underlying mechanisms. They also open up applied perspectives for the use of genetic markers to identify individuals with mutations conducive to masculinizationand more efficiently select XX trout lines, with almost all female offspring, which is sought because females have more interesting production performance and flesh quality.

See also


Fundings from :

  • FranceAgriMer
    france agrimer
  • Union européenne