RESUMEN
Among anurans, Bufonids are recognized for their retarded sex differentiation. However, few studies have addressed gonadal morphogenesis in this family. Here, we analyzed the early gonadogenesis in laboratory-reared Rhinella arenarum. Few germ cells were identified in the genital ridge at Gosner stage 26. At metamorphosis, somatic cells and germ cells were observed in the outer region of the undifferentiated gonad, whereas the central region was occupied by stromal tissue. A cortico-medullary organization was first recognized on Day 7 postmetamorphosis. The cortex was composed of germ cells and encompassing epithelial cells, whereas the medulla contained cells presumptively derived from the coelomic epithelium. Medullary somatic cells formed metameric knots along the length of the undifferentiated gonad. Consequently, a series of 12-14 gonomeres became recognizable externally. The first sign of ovarian differentiation was observed on Day 15 postmetamorphosis, when a cavity was formed within each gonomere. In contrast, testes were recognized by a uniform distribution of germ cells and intermingled somatic cells, as the division into cortex and medulla was lost. By Day 50 postmetamorphosis, the gonadal metameric organization was still apparent both in the ovaries and testes. Follicles containing diplotene oocytes were observed within the ovary. In the testis, an incipient lobular architecture was recognized without initiation of meiosis within the seminiferous cords. These observations reveal an extremely delayed gonadal development in R. arenarum, not reported previously for other anuran species. In addition, the late differentiation of the gonads contrasted with the early appearance of follicles in the Bidder's organ. Lastly, we observed that delayed metamorphs exhibited an undifferentiated gonad, demonstrating that gonadogenesis in this species is more dependent on somatic development than on age.
Asunto(s)
Bufonidae , Diferenciación Sexual , Masculino , Femenino , Animales , Gónadas , Testículo , Morfogénesis , América del SurRESUMEN
We studied the reproductive strategy, sexual system and growth of dientudo paraguayo Acestrorhynchus pantaneiro. After 2 years of monitoring in shallow areas of a floodplain lake from the lower Paraná basin (Argentina), it was evidenced that water temperature modulated gonadal maturation, but it was the river water level the synchronising stimulus that triggered spawning. This species exhibited a single annual breeding period from October to January, with most spawning activity in November. According to the von Bertalanffy growth curve, fish would reach autumn to winter months with LS of ~120 mm, already mature males. The first mature females were found at LS of 210 mm, becoming sexually mature between the second and third breeding seasons. This is the first integrative study that includes the body-length frequency distribution and sex differential size at first maturity and growth, and reports the presence of intersex gonads questioning its sexual pattern from gonochoristic to sequential hermaphrodite species. The sexual pattern, the multiple spawning behaviour and a medium to high absolute fecundity support the opportunistic and invasive behavior observed in previous contributions for this characiform species.
Asunto(s)
Characiformes , Femenino , Masculino , Animales , Maduración Sexual , Reproducción , Fertilidad , Gónadas , Estaciones del Año , BiologíaRESUMEN
Ivermectin (IVM) is one of the most widely used antiparasitics worldwide. It is a potent and effective drug for treatment and prevention of internal and external parasitic infections of livestock and humans. IVM is excreted unchanged in manure of treated animals. Thus, residues of IVM may reach aquatic systems, affecting non-target organisms such as fish. Although the presence of IVM in aquatic environments has been reported, a multilevel approach (from cellular to behavioral responses) is necessary to determine the health of exposed organisms and the environmental risks associated. The aim of the present study was to investigate the response of the Neotropical fish Prochilodus lineatus, one of the main target species of South American freshwater fisheries, exposed to environmental concentrations of IVM: low (0.5 µg L-1) and high (1.5 µg L-1). Behavioral responses were assessed in juvenile fish and included water column use, routine swimming, total distance travelled, total activity time and Maximum swimming speed achieved during the escape response. Biochemical/oxidative stress responses assessed included brain acetylcholinesterase (AChE), catalase (CAT) and glutathione S-transferase (GST) activities; total antioxidant competence against peroxyl radicals (ACAP) and lipid oxidative damage (TBARs). Hematological biomarker responses included blood glucose levels, hematocrit, hemoglobin concentration, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and mean corpuscular volume. Condition factor and hepatosomatic index were also calculated. The lowest IVM concentration caused a significant decrease in GST activity and maximum swimming speed during the escape response. Multivariate analysis with biochemical/stress and behavioral data revealed overall effects of IVM treatments. This multilevel analysis shows detrimental effects related to swimming behavior and predator avoidance which could affect population size and size-structure of P. lineatus. To our knowledge this is the first attempt to assess the effects of IVM on Neotropical fishes using an integrative approach based on biomarkers from different levels of biological organization.
Asunto(s)
Characiformes , Contaminantes Químicos del Agua , Acetilcolinesterasa , Animales , Explotaciones Pesqueras , Glutatión Transferasa , Ivermectina/toxicidad , Hígado , Contaminantes Químicos del Agua/toxicidadRESUMEN
Estrogenic chemicals are often detected in the aquatic environment and can negatively affect animal development and reproduction. In teleost fishes, the hormonal regulation during a critical period of larval development has a strong influence on gonadal sex differentiation; thus this process may be affected by the exposure to environmental estrogens. In this study, we first assessed the lethal acute toxicity of the natural estrogen 17ß-estradiol (E2) and the weaker estrogen mimics 4-tert-octylphenol (OP) and 4-nonylphenol (NP) on larval stages of the South American cichlid fish Cichlasoma dimerus. In a further experiment, we analyzed the effects of chronic waterborne exposure to E2 and OP on gonad development and sex differentiation. Exposure to high concentrations of E2 had a pronounced feminizing effect directing sex differentiation towards ovarian development, while testis development was inhibited at a lower, environmentally relevant concentration. Among OP-exposed fish, 15-38.5% of the males exhibited testicular oocytes (TOs), a commonly reported biomarker of estrogenic exposure. However, since TOs were also recorded in control males and the proportion of males with TOs was not significantly higher in OP treatments, their occurrence could not be attributed to OP exposure. In addition, TOs did not seem to impair male gonad development and functionality since normal spermatogenesis was observed in testes of OP-treated fish. These results indicate that E2 occurring in the South American aquatic environment may affect male reproductive development and pose a risk for wild C. dimerus, especially under prolonged exposure, while the effects of weaker xenoestrogens such as OP would be negligible for gonad development in this species. As illustrated by this study, the natural occurrence of TOs indicates that conclusions concerning the causes of this phenomenon must be drawn with care.
Asunto(s)
Cíclidos/crecimiento & desarrollo , Estradiol/toxicidad , Estrógenos/toxicidad , Fenoles/toxicidad , Animales , Femenino , Larva/efectos de los fármacos , Larva/crecimiento & desarrollo , Masculino , Ovario/efectos de los fármacos , Ovario/crecimiento & desarrollo , Diferenciación Sexual/efectos de los fármacos , Testículo/efectos de los fármacos , Testículo/crecimiento & desarrolloRESUMEN
Endosulfan (ES) is an organochlorine pesticide widely used in agriculture despite its high toxicity towards non-target organisms such as fish. It has been demonstrated that ES can cause negative effects on aquatic animals, including disruption of hormonal systems. However, the alterations produced by this pesticide on the reproductive axis of fish prior to sexual maturity, as well as possible modes of action have hardly been studied. This study aimed at assessing the effect of waterborne exposure to the pesticide ES on the reproductive axis during sexual differentiation of juveniles of the South American freshwater cichlid fish Cichlasoma dimerus. No mortality was observed due to ES subchronic exposure (90 days post-fertilization). Exposure to ES did not affect body weight nor morphometric parameters, indicating that larvae nutritional state was not affected. Timing of sexual differentiation, gonadal morphology and sex ratio were likewise not altered by ES. However, ES acted as an endocrine disrupting chemical in this species as the morphometry of gonadotropin-releasing hormones (GnRH) producing cells was altered. Exposure to ES altered nuclear area, cell area and nucleus/cytoplasm ratio of GnRH II neurons, and cell and nuclear area and diameter of GnRH III neurons. Interestingly, in our previous study, exposure before sex differentiation (30 day exposure) caused no alteration to GnRH II and III, and did alter GnRH I and FSH cells. These alterations could lead to changes in circulating hormone levels, especially when fish are exposed for prolonged periods, ultimately impairing reproductive fitness. C. dimerus juveniles can be an interesting biological model to perform toxicological studies with the intent to assess early disruption endpoints in the reproductive axis during development.
Asunto(s)
Cíclidos/fisiología , Endosulfano/toxicidad , Insecticidas/toxicidad , Neuronas/efectos de los fármacos , Diferenciación Sexual/efectos de los fármacos , Contaminantes Químicos del Agua/toxicidad , Análisis de Varianza , Animales , Disruptores Endocrinos/toxicidad , Agua Dulce , Hormona Liberadora de Gonadotropina/metabolismo , Gónadas/efectos de los fármacos , Hidrocarburos Clorados/toxicidad , Larva/efectos de los fármacos , Precursores de Proteínas/metabolismoRESUMEN
Endosulfan (ES), a persistent organochlorine pesticide, is widely used despite its toxicity to non-target animals. Upon reaching water bodies, ES can cause negative effects on aquatic animals, including disruption of hormonal systems. However, the action of ES on fish reproductive axis has been hardly studied thus far. The aim of the present work was to assess the endocrine disruptive potential of endosulfan on the pituitary gonadotropins levels and on the testes function due to ES in the South American freshwater fish Cichlasoma dimerus, using in vitro and in vivo approaches. In vitro experiments showed that ES inhibited the LH-stimulated steroidogenesis in gonads; no change was observed in gonadotropins release from pituitaries in culture. Laboratory waterborne ES (0.1, 0.3 and 1 µg/L) exposure for two months caused decrease in ßFSH pituitary content and γGT activity in the testes (Sertoli cell function marker). Testicular histology revealed pathologies such as scarce intermediate stages of spermatogenesis, release of immature germ cells into the lobular lumen, presence of foam cells and interstitial fibrosis. As FSH and FSH-mediated steroidogenesis regulate spermatogenesis and Sertoli cell function, the effect of ES on FSH could be responsible for the morphological alterations observed in testes. In vitro, ES disrupted steroidogenesis in gonads, therefore similar effects in vivo cannot be ruled out. Based on this evidence, ES exhibits an endocrine disruptive action on the reproductive axis of C. dimerus, causing disruption at the pituitary and/or at the gonad level. These effects could acquire ecological significance under prolonged exposure to the pesticide in nature.
Asunto(s)
Cíclidos , Endosulfano/toxicidad , Ovario/efectos de los fármacos , Testículo/efectos de los fármacos , Contaminantes Químicos del Agua/toxicidad , Animales , Células Cultivadas , Endosulfano/análisis , Femenino , Gonadotropinas Hipofisarias/metabolismo , Masculino , Hipófisis/química , Hipófisis/efectos de los fármacos , Contaminantes Químicos del Agua/análisisRESUMEN
The aim of this study was to describe the time-course of estrogen-induced gene expression, corresponding plasma protein detection and histological alterations after cessation of octylphenol (OP) exposure of Cichlasoma dimerus, to test differential responses of biomarkers suitable for environmental monitoring. Male fish were exposed to a nominal concentration of 150 µg/L OP for 28 days, and later transferred to OP-free water aquaria for 1, 3, 7, 14, 21 or 28 days. Blood and mucus samples were obtained in order to analyze vitellogenin (VTG) and zona pellucida (ZP) proteins by Western blot; liver samples were used for gene expression and to assess tissue damage and further recovery of all the analyzed endpoints. Partial sequences of C. dimerus VTG and Naâº/Kâº-ATPase were obtained. Comparison with VTGs of several teleosts supports that the partial sequence obtained for C. dimerus belongs to VTGAb type. ZP and VTG expression was highly up-regulated by OP. Immunoreactive (ir-) bands of 62, 52 and 50 kDa for ZP and 140, 103, 75 and 64 kDa for VTG, were detected after 28 days of OP exposure in plasma and mucus samples. After transfer of treated fish to clean water, ZP ir-bands in plasma disappeared rapidly (day 3), while VTG ir-bands decreased gradually; no ir-bands were detected on day 28 of recovery. Similarly, ZPB transcripts abruptly returned to background levels (day 3), earlier than for ZPC (day 7) or VTG (day 14). Liver from OP treated fish showed tissue disarrangement, eccentric and euchromatic hepatocytes nuclei and intense perinuclear basophilia. After the recovery period, these changes were still evident though less pronounced, accounting for irreversibility of tissue damage or the requirement for a longer period of depuration. The present results confirm that for biochemical and molecular biomarkers, such as induction of female proteins in male fish exposed to OP, complete recovery is achieved after adequate time of depuration (28 days). Male ZPB expression reflects a recent exposure to estrogenic contaminants, while VTG may reveal past exposures. The combination of biomarkers with different temporal responses such as C. dimerus ZP and VTG provides a more comprehensive interpretation of pollution status.
Asunto(s)
Cíclidos/fisiología , Estrógenos/metabolismo , Fenoles/toxicidad , Contaminantes Químicos del Agua/toxicidad , Secuencia de Aminoácidos , Animales , Proteínas del Huevo/genética , Proteínas del Huevo/metabolismo , Disruptores Endocrinos/toxicidad , Estradiol/administración & dosificación , Estradiol/farmacología , Femenino , Regulación de la Expresión Génica/efectos de los fármacos , Masculino , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , Datos de Secuencia Molecular , Filogenia , Isoformas de Proteínas , Subunidades de Proteína , ARN Mensajero/genética , ARN Mensajero/metabolismo , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , ATPasa Intercambiadora de Sodio-Potasio , Glicoproteínas de la Zona PelúcidaRESUMEN
Endocrine-disrupting chemicals can influence the hypothalamus-pituitary-gonad axis and possibly affect reproduction in vertebrates. We analyzed the effect of 30-day endosulfan (ES) exposure in sexually undifferentiated larvae of the cichlid fish Cichlasoma dimerus. The number, area, mean cytoplasmic and nuclear diameter, and mean cytoplasmic optical density of gonadotropin-releasing hormone (GnRH) I, II, and III immunoreactive (ir-) neurons and ß follicle-stimulating hormone (ßFSH) ir-cells were measured. Animals exposed to the highest ES concentration (0.1 µg/l) showed a decrease in GnRH I nucleus/cytoplasm area ratio upon exposure. Nuclear area and mean nuclear diameter of ßFSH ir-cells was higher in ES treated fish. ßFSH nucleus/cytoplasm area ratio was high in exposed animals, and animals exposed to 0.1 µg/l ES showed smaller mean cytoplasmic optical density. These findings suggest that ES affects GnRH I and ßFSH protein synthesis/release. However, these responses seem to be insufficient to affect gonadal differentiation at this stage of development.