Dynamics of ovarian maturation throughout the reproductive cycle of the Neotropical cichlid fishCichlasomadimerus(Teleostei, Cichliformes)

Abstract

In this study, we analyzed gene expression profiles, plasma steroids concentrations, and gonadal morphology throughout the reproductive cycle of female Cichlasoma dimerus (Heckel, 1840), a monogamous cichlid fish exhibiting social hierarchies. Fish were analyzed at six phases encompassing their annual cycle, namely resting (during the nonreproductive period), prespawning, 30 h post spawning, 4 days post spawning, 10 days post spawning, and subordinate (during the reproductive period). The histological and histomorphometric analysis showed that C. dimerus exhibits asynchronous ovarian development. Similar to resting females, subordinate females showed low gonadosomatic index, reduced expression levels of vitellogenin (vtgAb), zona pellucida (zpB), gonadal aromatase (cyp19a1A), and low concentrations of plasma sex steroids, thus indicating that social intimidation by dominant conspecifics elicited reproductive arrest. In reproductively active females, a direct positive correlation between plasma estradiol, vtgAb expression, percentage of late vitellogenic oocytes, and gonadosomatic index was observed. These parameters were maximal at the prespawning phase, decreased at 30 h post spawning and 4 days post spawning, and then reached a peak at 10 days post spawning. Our results indicate that female C. dimerus become spawning capable after 10 days post spawning, coincidently with the shortest time interval between successive spawns recorded in captivity.

Gonadosomatic index as a confounding variable in fish‐based screening assays for the detection of anti‐estrogens and nonaromatizable androgens

“…Thus the first objective of the present study was to assess the relationship between GSI and baseline vtg and erα expression in female fathead minnows. The positive, significant correlations between GSI and vtg and erα expression identified in present study suggest that GSI influences the baseline expression of estrogen‐responsive genes, congruent with the relationship previously shown in the literature (Panprommin et al ; Nagler et al ; Tingaud‐Sequeira et al ; Varela et al ). Because exposures to anti‐estrogens and nonaromatizable androgens typically lead to decreases in hepatic expression of vtg and erα in female fish (Villeneuve et al ; Zhang et al ; Dorts et al ; Sun et al ), it is reasonable to expect that differences in female GSI values may influence the magnitude of vtg and erα down‐regulation following exposures to anti‐estrogens and nonaromatizable androgens.…”

“…The hypothesis that the reproductive status of an organism can influence their response to REDC exposure is based on previous evidence across multiple teleost species showing that reproductive status, as assessed via a variety of different metrics including GSI, is associated with baseline vtg and erα expression (Funkenstein et al ; Burki et al ; Panprommin et al ; Pousis et al ; Nagler et al ; Tingaud‐Sequeira et al ; Varela et al ). Thus the first objective of the present study was to assess the relationship between GSI and baseline vtg and erα expression in female fathead minnows.…”

“…Although the influence of organism sex is taken into account in most REDC screening assays, it is not the only biological variable known to influence baseline gene expression of vtg and erα . Several studies have provided evidence suggesting that the expression of estrogen‐responsive genes in female fish is related to various measures of reproductive status, including gonadosomatic index (GSI), oocyte diameter, and ovary stage (Funkenstein et al ; Burki et al ; Panprommin et al ; Pousis et al ; Nagler et al ; Tingaud‐Sequeira et al ; Varela et al ). Thus it is hypothesized that the reproductive status of female fathead minnows influences their response to REDCs.…”

Ovarian cycle in Devario aequipinnatus with emphasis on oogenesis

“…Resumption of the meiotic process initiates the maturation stage (Abascal & Medina, 2005), which is completed with fertilization (Quagio-Grassiotto et al ., 2013). In this stage, the germ vesicle (nucleus) migrates towards the micropyle region (Honji et al ., 2006; Quagio-Grassiotto et al ., 2011; Cassel et al ., 2017a; Varela et al ., 2017), as observed for D. aequipinnatus . However, for D. aequipinnatus , the presence of lipid droplets was not observed.…”

“…Stain: haematoxylin and eosin. Quagio-Grassiotto et al, 2011;Cassel et al, 2017a;Varela et al, 2017), as observed for D. aequipinnatus. However, for D. aequipinnatus, the presence of lipid droplets was not observed.…”