Genetic architecture of sex determination in fish: applications to sex ratio control in aquaculture

Abstract

Controlling the sex ratio is essential in finfish farming. A balanced sex ratio is usually good for broodstock management, since it enables to develop appropriate breeding schemes. However, in some species the production of monosex populations is desirable because the existence of sexual dimorphism, primarily in growth or first time of sexual maturation, but also in color or shape, can render one sex more valuable. The knowledge of the genetic architecture of sex determination (SD) is convenient for controlling sex ratio and for the implementation of breeding programs. Unlike mammals and birds, which show highly conserved master genes that control a conserved genetic network responsible for gonad differentiation (GD), a huge diversity of SD mechanisms has been reported in fish. Despite theory predictions, more than one gene is in many cases involved in fish SD and genetic differences have been observed in the GD network. Environmental factors also play a relevant role and epigenetic mechanisms are becoming increasingly recognized for the establishment and maintenance of the GD pathways. Although major genetic factors are frequently involved in fish SD, these observations strongly suggest that SD in this group resembles a complex trait. Accordingly, the application of quantitative genetics combined with genomic tools is desirable to address its study and in fact, when applied, it has frequently demonstrated a multigene trait interacting with environmental factors in model and cultured fish species. This scenario has notable implications for aquaculture and, depending upon the species, from chromosome manipulation or environmental control techniques up to classical selection or marker assisted selection programs, are being applied. In this review, we selected four relevant species or fish groups to illustrate this diversity and hence the technologies that can be used by the industry for the control of sex ratio: turbot and European sea bass, two reference species of the European aquaculture, and salmonids and tilapia, representing the fish for which there are well established breeding programs.

Heat-induced masculinization in domesticated zebrafish is family-specific and yields a set of different gonadal transcriptomes

“…In other species, such as Nile tilapia, which can also tolerate high temperatures, the presence of neomales has been strongly suggested in Kpandu and Koka natural populations (75). If they reach adulthood and reproduce, neomales can produce sex-biased (75% females) progeny in a ZZ/ZW system, if the WW genotype is viable (76), or 100% females in a XX/XY system (22). Severely biased sex ratios may have potentially detrimental consequences for population viability (77).…”

Single nucleotide polymorphism markers with applications in aquaculture and assessment of its impact on natural populations

“…Females and males can differ in growth rate, which has implications for aquaculture. Sex manipulation is commonly practiced in aquaculture for example in Nile tilapia, Oreochromis niloticus (Mair et al, 1991;Garcia et al, 2016;Sansuwan et al, 2017), (Calhoun and Shelton, 1983), gilthead sea bream, S. aurata (Loukovitis et al, 2012), European sea bass, Dicentrarchus labrax (Martinez et al, 2014) and turbot, S. maximus (Robledo et al, 2015). Early sexual maturation (grilsing) retards growth, increases production times and affects flesh quality in aquaculture.…”

Neuroendocrine disruption of organizational and activational hormone programming in poikilothermic vertebrates

“…While there is ample evidence and reviews of organizational-activational effects in mammals and birds (Adkins-Regan 1999; Balthazart et al 1996; 2009; Morris, et al 2004; Arnold and Breedlove 1985; Phoenix et al 1959; Ottinger and Dean 2011), this concept has not been fully considered in poikilothermic species that may exhibit a wide range of developmental and reproductive strategies. Most of these species also lack sex chromosomes, yet still have genotypic sex determination (GSD) and some possess environmental sex determination (ESD) dependent upon temperature (TSD) or behavior to determine whether the brain and gonads differentiate along male or female pathways (Blazquez and Somoza 2010; Kohno et al 2014; Merchant-Larios and Diaz-Hernandez 2013; Devlin and Nagahama 2002; Martinez et al 2014; Godwin 2010). Some examples of poikilothermic species with TSD include Atlantic silverside fish ( Menidia menidia ), painted turtles, ( Chrysemys picta ), and all crocodilians (Blazquez and Somoza 2010; Kohno et al 2014; Merchant-Larios and Diaz-Hernandez 2013).…”