Ontogeny and Dynamics of the Gonadal Development, Embryogenesis, and Gestation in <b><i>Xenotoca eiseni</i></b> (Cyprinodontiformes, Goodeidae)

Abstract

We characterized the ontogeny and dynamics of gonadal development, embryogenesis, and gestation in captive stocks of the viviparous redtail splitfin,&lt;i&gt; Xenotoca eiseni&lt;/i&gt;. Using histology, we showed that gonads were fully differentiated at the time of birth with a male:female sex ratio of 1:1 in the captive stock. External secondary sex features included a modified anal fin and a distinctive orange tail coloration. These features first appeared at 4 weeks after birth and were discriminative for males thereafter. There was no sex-related dichotomy in body size, and &lt;i&gt;X. eiseni&lt;/i&gt; reached sexual maturity at approximately 12 weeks of age. We found no evidence for sperm storage in females. Gestation normally took 6 weeks, and there was a positive correlation between female body size and the number of offspring produced, with up to 27 offspring for a single pregnancy. Yolk is the main food source for developing embryos for the period up to 2 weeks, and thereafter, trophotaeniae in embryos act as nutrient exchange surfaces in the ovarian lumen, which subsequently undergo complete regression within 2 weeks of birth. In our final analysis, we discuss the great potential of &lt;i&gt;X. eiseni&lt;/i&gt; as a model for studying the effects of chemicals on sexual development.

Effects of maternal exposure to environmentally relevant concentrations of 17α-ethinyloestradiol in a live bearing freshwater fish, Xenotoca eiseni (Cyprinodontiformes, Goodeidae)

“…The timing of the gonadal sexual differentiation process has not been determined for X. eiseni and therefore we do not know if sexual differentiation had started in the developing offspring before the start of the EE2 exposure. However, this is likely to have been the case if we compare the ontogeny of sexual differentiation in this species (Tinguely et al, 2020) with the barred splitfin, another goodeid with a similar gestation period of 6-8 weeks (Guerrero-Estévez and Moreno-Mendoza, 2012).…”

“…The eelpout, least killifish and mosquitofish all have relatively long gestation periods of between four to more than six months (Brande-Lavridsen et al, 2013;Klerks, 2015, 2014;Hedman et al, 2011;Rasmussen et al, 2002;Skov et al, 2010) and highly complex reproductive strategies including sperm storage and superfetation, which complicates their use as models in ecotoxicological studies. In contrast, the redtail splitfin (Xenotoca eiseni), a goodeid fish, has a gestation time of a few weeks only (Parenti, 2005;Tinguely et al, 2020) and is potentially practically more suitable as a species for testing effects of maternally transferred toxicants. A shorter gestation however does mean a shorter time window for assessing the bioaccummulative effects of contaminants.…”

Cubam receptor-mediated endocytosis in hindgut-derived pseudoplacenta of a viviparous teleost Xenotoca eiseni

“…The family Goodeidae is a freshwater small teleost distributed in Mexico, which includes approximately 40 viviparous species [6]. They possess trophotaenia, which is a hindgut-derived pseudoplacenta that absorbs the maternal component [7,8]. Trophotaenia is a ribbon-like structure consisting of a single epithelial layer, internal blood vessels, and connective tissues [9,10].…”

“…The family Goodeidae is a freshwater small teleost distributed in Mexico, which includes approximately 40 viviparous species [6]. They possess trophotaenia, which is a hindgut-derived pseudoplacenta that absorbs the maternal component [7,8].…”

Cubam receptor-mediated endocytosis in hindgut-derived pseudoplacenta of a viviparous teleost Xenotoca eiseni

“…The family Goodeidae comprises freshwater small teleosts distributed in Mexico, and includes approximately 40 viviparous species ( Foster and Piller, 2018 ). They possess trophotaeniae, which are hindgut-derived pseudoplacentas that absorb the maternal component ( Turner, 1940 ; Tinguely et al, 2019 ). The trophotaenia is a ribbon-like structure consisting of a single epithelial layer, internal blood vessels and connective tissues ( Turner, 1933 , 1937 ).…”