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

Dernière mise à jour : Mai 2018

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NeoBio

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

NeoBio
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

Partners:

Fundings from :

  • FranceAgriMer
    france agrimer
  • Union européenne
    UE