Sex determination and sex control in salmonidae

The Salmonidae family comprises three sub‐families (Coregoninae, Thymallinae and Salmoninae), with 11 genera and about 66 species. Salmonid farming has grown considerably in the last fifty years, with Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) being the main farmed species, and with an increasing production of large size fish that has required the development of all‐female or sterile populations. Salmonids are gonochoristic fishes with a genotypic sex determination (GSD) system, classically described as male heterogametic (XX/XY). Some temperature effects (GSD + TE) have been reported in a limited number of cases. The master sex determining gene, sdY (sexually dimorphic on the Y chromosome), has been characterized in rainbow trout, and is conserved in many salmonid species. sdY is expressed very early (around hatching in rainbow trout) during gonadal differentiation, long before the initiation of histological sex differentiation. In addition, other genes exhibit a sex‐dimorphic expression, particularly those involved in steroid synthesis, leading to a hypothesis in favor of a key role of estrogens in inducing and maintaining ovarian differentiation in salmonids. Sex control in salmonids is mostly carried out by producing XX neomales that give rise to all‐female populations after crossing with wild‐type females. These XX neomales are usually produced by masculinization of females, using an androgen treatment (the most commonly used being 17α‐methyltestosterone) administered in the food from the first feeding of larvae. Limits and concerns of such methods are discussed, and other potential approaches are foreseen