Environmental factors and sexual differentiation in Poecilia sphenops Valenciennes (Pisces: Poeciliidae)

Abstract

Because environmental factors play an important role in the sexual proportions in fish and given that the studies that evaluate the interactions of such factors are scarce, the purpose of this work was to determine the combined effect of pH/temperature (23, 26 and 29 °C; pH 6, 7 and 8) on sex determination of Poecilia sphenops Valenciennes. The trial started with newborn organisms (n = 180) that were maintained in aquaria for 6 months until they could be separated by sex. Afterwards, nine groups of four females (0.81–1.48 g) and two males (0.36–0.63 g) were distributed in 20‐L aquaria until fertilization, gestation and offspring birth took part. The offspring were grown under the same conditions until they reached sexual maturity. The results indicated the strong interaction of the factors (P < 0.05) with a lower male/female ratio at pH 7 both at 23 °C (M/F = 0.12) as well as at 30 °C (M/F = 0.10) and higher ratios at pH 8 at similar temperatures (M/F = 0.7) to 23 °C and (M/F = 0.6) to 26 °C. The females dominated in all the combinations; the least favourable combinations were 23 and 26 °C at pH 8 with 0.7 and 0.6 M/F ratios respectively. The results obtained in the laboratory explain very closely the behaviour of the population of P. sphenops from Oaxaca in the natural environment that can be used in aquaculture for baitfish production and also for aquaculture purposes.

Environmental stress-induced testis differentiation: Androgen as a by-product of cortisol inactivation

“…In these species, acidic and alkaline conditions induced male-and female-biased sex ratios, respectively(Oldfield et al, 2006;Römer and Beisenherz, 1996;Rubin, 1985). In contrast, another Poeciliid (Poecilia sphenops) showed the opposite gender-bias effects in combination with rearing temperature(Barón et al, 2002).2.3. TemperatureAmongthe effectors of ESD, water temperature is the most studied factor in teleosts (Temperature-dependent sex determination or TSD) (Baroiller et al, 2009; Kobayashi et al, 2013; Ospina-Álvarez and Piferrer, 2008; Sandra and Norma, 2010).…”

Gonad Ontogeny and Sex Differentiation in a Poeciliid, Gambusia holbrooki: Transition from a Bi- to a Mono-Lobed Organ

“…Hence, an effective masculinisation treatment must be administered via the mothers, i.e., before female embryos have undergone sex differentiation in G. holbrooki. However, in poeciliid species such as P. sphenops [79], post-natal treatment of testosterone is sufficient for effective masculinisation, suggesting species-specific differences.…”

Sex Determination and Differentiation in Teleost: Roles of Genetics, Environment, and Brain

“…In some environmental sex determination species, the pH of the water can influence sex differentiation. Acidic water induces masculinization in the Poecilia melanogaster [26], Poecilia sphenops [170], and Pelvicachromis pulcher [70]. The tambaqui (Colossoma macropo-mum), native species to Brazil, has a vast range of pH (4-7.2) as natural habitat [171], and in farming conditions, it sustains pH 4.0-8.0.…”