RESEARCH ARTICLE

A novel sex-determining Q n2 di content [1]. Instances of both XX/XY male heterogam- even sex ratio can be expected in species with genetic Palaiokostas et al. BMC Genomics (2015) 16:171 DOI 10.1186/s12864-015-1383-xMany species of farmed fish exhibit sexual dimorph-ism in a range of traits of commercial importance, Stirling FK9 4LA, Scotland, UK Full list of author information is available at the end of the articleetic and WZ/ZZ female heterogametic sex-determining systems can be found in fish, while the fact that spon-taneous sex-reversed XX males are generally fully fertile indicates that sex-determining regions can also be lo-cated on autosomes. Even though the YY genotype is sex determination. However, departures from an equal sex ratio have been observed both in population and family studies, stressing the complexities of sex-determination in fish. Distorted population or family sex ratios are likely to be due to hormonal effects, complex genetic sex deter-mination or interaction between genetic and environmen-tal factors [4,5]. Environmental effects on sex ratios may vary even within species [6]. * Correspondence