Sex ratios in offspring of sex‐reversed sea bass and the relationship between growth and phenotypic sex differentiation

Abstract

Groups of sexually undifferentiated sea bass Dicentrarchus labrax were fed with the androgen 17 -methyltestosterone (MT) during sex differentiation. MT treatment increased males from 79 3% in the controls (the usual 3 : 1 male : female sex ratio of cultured sea bass) to 100 0%, implying that in the treated groups one out of each five resulting males was a masculinized female (neomale). Thirteen males from the MT treated groups were taken as the parental generation and their sperm used to individually fertilize a pool of eggs from unrelated females. The probability of having at least one neomale was 95% and most probably two or three of the males used were neomales. The offspring from each family were reared separately under the same environmental conditions. Samples were taken at 11 and 15 months of age, during and after sex differentiation, respectively. Results showed that females predominated among the larger fish whereas males and undifferentiated fish predominated among the smaller ones. Intersexes exhibited an intermediate size. All fish with a body length smaller than 12 cm were undifferentiated. These results suggest that sex differentiation is more dependent on length than on age. At 15 months, sex ratios were male-biased in all families, except one (females ranged from 5 to 50%) and only two families had sex ratios not significantly different from 1 : 1, suggesting that the mechanism of sex determination in the sea bass is not of a XX/XY or ZW/ZZ type since no family exhibited a female-biased progeny, as would be expected from both types. Results support the hypothesis that factors other than genetic, i.e., environmental, may act epigenetically on the sex determination mechanisms of sea bass, as has been demonstrated in other fishes. 1999 The Fisheries Society of the British Isles

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

“…European sea bass females differentiate earlier, are bigger, and mature later than males (Blázquez et al, 1999; Navarro-Martín et al, 2009a; Díaz et al, 2013). While still sexually undifferentiated, European sea bass gonads can be influenced by environmental abiotic factors or external factors such as sex steroids (Navarro-Martín et al, 2009a), but once sex is determined remains throughout life (Zanuy et al, 2001).…”

“…As in most teleosts, sea bass does not show sex chromosomes (Devlin and Nagahama, 2002). Female homogamety (XX) has been ruled out since sex ratios of normal diploid and gynogenetic offspring are equivalent (Felip et al, 2002), and offspring from masculinized females is not female-biased (Blázquez et al, 1999). Other data from hormone-treated fish suggested that male homogamety with environmentally male-biased sex ratio would still be a possibility (Vandeputte et al, 2007).…”

“…In the European sea bass, gonads remain undifferentiated during post-larval stages until fish attain about 8 cm standard length, usually at about 5–6 months of age (Bruslé and Roblin, 1984; Blázquez et al, 1999; Navarro-Martín et al, 2009a; Díaz et al, 2013). European sea bass females differentiate earlier, are bigger, and mature later than males (Blázquez et al, 1999; Navarro-Martín et al, 2009a; Díaz et al, 2013).…”

Can Myxosporean parasites compromise fish and amphibian reproduction?

“…In sea bass, the presence of ovarian tissue in the testes of non-parasitized males (ovo-testis) has been described (Blázquez et al 1999). However, a higher percentage of ovo-testis is found in males infected by S. testicularis than in uninfected ones under the same conditions (A. Sitjà-Bobadilla 1991, unpublished data).…”

Genomic Approaches to Study Genetic and Environmental Influences on Fish Sex Determination and Differentiation

“…7), where sex ratios are the product of both genetic (polygenic sex determination mechanism) (Vandeputte et al 2007) and environmental (temperature) influences (Piferrer et al 2005). In this species, several studies have shown that there is an early association between growth rates and sex (Blázquez et al 1999), with females being among the largest fish and males being among the smallest ones (Blázquez et al 1999; Saillant et al 2001; Vandeputte et al 2007). In addition, sexual growth dimorphism is present at the time of marketing when animals reach 300–400 g (Saillant et al 2001; Navarro-Martín et al 2009a).…”