Different Stages Of Gonadal Development Research Articles

A Na+ channel receptor of FMRFamide in the cephalopod Sepiella japonica: Identification, characterisation, and expression profiling during different stages of gonadal development

FMRFamide, a member of the neuropeptide family, is involved in numerous physiological processes. FMRFamide-activated sodium channels (FaNaCs) are a family of non-voltage-gated, amiloride-sensitive, Na+-selective channels triggered by the neuropeptide FMRFamide. In the present study, the full-length cDNA of the FaNaC receptor of Sepiella japonica (SjFaNaC) was cloned. The cDNA of SjFaNaC was 3004 bp long with an open reading frame (ORF) of 1812 bp, encoding 603 amino acid residues with no signal peptide at the N-terminus. Sequence analysis indicated that SjFaNaC shared a high identity with other cephalopods FaNaCs and formed a sister clade with bivalves. The protein structure was predicted using SWISS-MODEL with AcFaNaC as the template. Quantitative real-time PCR (qRT-PCR) revealed that SjFaNaC transcripts were highly expressed in both female and male reproductive organs, as well as in the optic lobe and brain of the central nervous system (CNS). Results of in situ hybridisation (ISH) showed that SjFaNaC mRNA was mainly distributed in the medulla and deep retina of the optic lobe and in both the supraesophageal and subesophageal masses of the brain. Subcellular localisation indicated that the SjFaNaC protein was localised intracellularly and on the cell surface of HEK293T cells. In summary, these findings may lay the foundation for future exploration of the functions of SjFaNaC in cephalopods.

Identification and Expression Profile of a Neuropeptide LFRFamide-Like Gene During Different Stages of Gonadal Development in the Cephalopod Sepia pharaonis

Identification and Expression Profile of a Neuropeptide LFRFamide-Like Gene During Different Stages of Gonadal Development in the Cephalopod Sepia pharaonis

Comparative Transcriptome Analysis Reveals the Role of Ribosome Reduction in Impeding Oogenesis in Female Triploid Crassostrea Gigas.

The fecundity of triploid female Crassostrea gigas exhibited significant variation and was lower compared to diploid individuals. Previous studies categorized mature stage triploid female C. gigas into two groups: female α, characterized by a high number of oocytes, and female β, displaying few or no oocytes. To investigate the molecular mechanisms underlying irregular oogenesis and fecundity differences in triploid C. gigas, we performed a comparative analysis of gonad transcriptomes at different stages of gonadal development, including female α, female β, and diploids. During early oogenesis, functional enrichment analysis between female diploids and putative female β triploids revealed differently expressed genes (DEGs) in the ribosome and ribosome biogenesis pathways. Expression levels of DEGs in these pathways were significantly decreased in the putative female β triploid, suggesting a potential role of reduced ribosome levels in obstructing triploid oogenesis. Moreover, to identify regulatory pathways in gonad development, female oysters at the early and mature stages were compared. The DNA repair and recombination proteins pathways were enriched in female diploids and female α triploids but absent in female β triploids. Overall, we propose that decreased ribosome biogenesis in female triploids hinders the differentiation of germ stem cells, leading to the formation of a large number of abnormal germ cells and ultimately resulting in reduced fecundity. The variation in fertility among triploids appeared to be related to the degree of DNA damage repair during female gonad development. This study offers valuable insights into the oogenesis process in female triploid C. gigas.

Evolution and gene expression of matrix metalloproteinase gene family during gonadal development in Scatophagus argus.

During the reproductive cycle of Scatophagus argus (S. argus), their gonads undergo degeneration and re-maturation including the degradation of proteins in the extracellular matrix (ECM). Matrix metalloproteinases (MMPs), a family of zinc proteases, play a crucial role in ECM degradation. Our aim was to identify the MMP gene family of S. argus and determine their gene expression levels across various stages of gonadal development. The MMP gene family of S. argus in the genome was identified by using basic Local Alignment Search Tool (BLAST) and HMMER. Phylogenetic tree and synteny analysis were performed to investigate the evolutionary past of the MMP gene family. The gonads of 18 S. argus (9 males and 9 females) were dissected and a quantitative reverse transcription polymerase chain reaction (RT-qPCR) was conducted to investigate the expression levels of MMP genes across different stages of gonadal development. Twenty-three MMP family genes were identified in the genome of S. argus. We divided the MMP gene family into 4 categories and found that teleosts exhibit a higher MMP gene copy number relative to other vertebrates. By sampling S. argus at different stages of gonadal development, we observed an upregulation in relative expression levels of 11 MMP genes in the testis or ovary. Ten MMP genes (mmp2, 9, 14a, 15a, 15b, 16a, 17a, 23b and 24) showed higher mRNA expression in the testis compared to the ovary and mmp28 had higher expression during ovarian development. The tissue distribution results demonstrated that the gills exhibited the lowest relative expression level among all tissues examined. However, 6 genes (mmp2, 9, 14a, 15a, 15b, and 16a) had relatively high expression in all tissues. The result suggested that teleost-special whole genome duplication was mainly responsible for the formation of the MMP gene family in teleosts. Expression patterns of MMP genes indicated that mmp2, 9, 14a, 15a, 15b, 16a, 17a, 23b and 24 played a vital role in testicular development while mmp28 was more important for ovarian development. Limitaion: Further studies are needed to determine their protein expressions in gonadal development and precise mechanism in gonadal differentiation. The study enhances our understanding of the MMP gene family in evolution of teleost and provides valuable insights for further research on MMPs in S. argus.

Genome-wide identification, evolution and expression of TGF-β signaling pathway members in mandarin fish (Siniperca chuatsi)

Members of the transforming growth factor β (TGF-β) signaling pathway regulate diverse cellular biological processes in embryonic and tissue development. We took mandarin fish (Siniperca chuatsi) as the research object to identify all members of the TGF-β signaling pathway, measure their expression pattern in the key period post hatching, and further explore their possible role in the process of sex regulation. Herein, we identified eighty-three TGF-β signaling pathway members and located them on chromosomes based on the genome of mandarin fish. TGF-β signaling pathway members were highly conserved since each TGF-β subfamily clustered with orthologs from other species. Transcriptome analysis, qRT–PCR and in situ hybridization demonstrated that most mandarin fish TGF-β signaling pathway members presented stage-specific and/or sex-dimorphic expression during gonadal development, and different members of the TGF-β signaling pathway participated in different stages of gonadal development. Taken together, our results provide new insight into the role of TGF-β signaling pathway members in the sex regulation of mandarin fish.

Use of quantitative real-time PCR to select reference genes in the testis and ovary of Apostichopus japonicus during the breeding period

Gonads play a critical role in the reproduction of sea cucumbers, and their development is regulated by a large number of genes. To date, the ideal reference genes (RGs) for studying sea cucumber gonadal development have not been reported. In this study, we selected ten RGs and conducted quantitative real-time PCR analysis to identify the most stable among Apostichopus japonicus gonads at four different stages of gonadal development. We used ∆Cq, GeNorm, NormFinder, BestKeeper, and RefFinder to evaluate the stability of candidate genes. EF1β and Grb2 together were the preferred combination of stable RGs among all of the gonad samples and for the ovaries alone. UBQ combined with RPS4 was the best combination of stable RGs in the testes. This study aimed to provide a basis for analysis of differences in gene expression related to gonadal development in sea cucumbers, and the results provide valuable information for further studies of the molecular mechanisms involved in sea cucumber gonadal development.

Environmental Factors and Genetic Diversity as Drivers of Early Gonadal Maturation: A Gonadosomatic Index Based Investigation on Indian Shad, Tenualosa ilisha Population of Bangladesh

In recent years, attaining gonadal maturation in smaller Hilsa (Tenualosa ilisha) has become a burning issue for Hilsa fishery of Bangladesh. Causes of early maturation are not yet clearly understood. Along with environmental parameters, genetic differentiation within the population was hypothesized as the main driver, and therefore, assessing the correlation between gonadosomatic index (GSI) and environmental factors and analyzing genetic diversity were set as objectives of the present study. To address these complex issues, six diverse habitats across Bangladesh were chosen for Hilsa sample collection. For GSI, gonad was dissected from fresh fish and preserved in Bouin’s fluid for histological observation. Water quality parameters such as temperature, dissolved oxygen, pH, and salinity were also assessed. 35 fish from each habitat were used to extract and amplify DNA through the PCR technique, and genetic diversity was examined. Further, to draw a firm conclusion, the phylogenetic tree of the Hilsa population was developed by the unweighted pair-group method of arithmetic mean method based on the Cyt b gene of mitochondrial DNA. Results of GSI studies revealed that peak spawning months of T. ilisha were in October and February, where October showed the highest values in all six habitats. Histological examination showed different stages of gonadal development in different sizes and ages of Hilsa. Among all sampling sites, no statistical difference was observed for GSI value; however, smaller sized and aged Hilsa being ripped were evident in Gaglajur Haor and Kali River. Among the observed water quality parameters, temperature correlated with GSI strongly. Increased GSI was observed with temperature augmentation from downstream to upper stream, irrespective of body size and age. A perplex correlation between dissolved oxygen of observed habitats and GSI was executed. Other physico-chemical parameters viz. pH and salinity exhibited weak and moderate positive association with the GSI, respectively. Haplotype diversity of mitochondrial DNA divided the Hilsa population into three possible sub-populations, where the most distant group (Gaglajur Haor and Kali River) was subjected to early gonadal maturity. Results of this study make clear conclusions regarding the role of environmental and genetic factors on early gonadal maturations, pointing fingers at the curse of climate change and anthropogenic stressors for the migration of the Hilsa fishery of Bangladesh.

Dimorphic Expression of Selected Genes in Lepidocephalus thermalis using Cross-Specific Primers

Background: The existence of two distinct forms within a species that differ in one or more characteristics is known as dimorphism. The gonads are the primary organs in teleost to show sexual dimorphism. Lepidocephalus thermalis belongs to the Cobitidae family. No expression study on the developmental stages was done on this species. Since there is no specific primers reported for L. thermalis, the study has been carried out with the help of the specific primers of catfish. Methods: qRT- PCR is an acknowledged method for gene expression analysis due to its precision and reproducibility. In the current study, the expression of 14 different transcription factors involved in sex differentiation of Indian spiny loach during different developmental stages was analyzed using qRT- PCR and has been compared among the different stages of gonadal development for that transcription factor. Results: Gene expression patterns have been obtained from the total RNA isolated from MSG (Meso nephric gonadal complex), medium stage ovary, medium stage testis, large stage ovary and large stage testis. From the study, it has been analyzed that only sf1 has higher expression in testis and all the other transcription factors has shown higher expression in ovary.

Gnrh1-Induced Responses Are Indirect in Female Medaka Fsh Cells, Generated Through Cellular Networks.

Reproductive function in vertebrates is stimulated by GnRH that controls the synthesis and release of the two pituitary gonadotropins, FSH and LH. FSH and LH, which regulate different stages of gonadal development, are produced by two different cell types in the fish pituitary. This is in contrast to the situation in mammals and birds, and it enables investigation of their differential regulation. In the present study, we used fluorescence in situ hybridization to show that Lh cells in adult female medaka express Gnrh receptors, whereas Fsh cells do not. This result was confirmed by patch-clamp recordings and by cytosolic Ca2+ measurements on dispersed pituitary cells, where Lh cells, but not Fsh cells, responded to Gnrh1 by biphasic alteration in action-potential frequencies and cytosolic Ca2+ levels. In contrast, both Fsh and Lh cells are able to respond to Gnrh1 in brain-pituitary tissue slices both electrically and by elevating the cytosolic Ca2+ levels. Using Ca2+ uncaging in combination with patch-clamp recordings and cytosolic Ca2+ measurements, we show that Fsh and Lh cells form homotypic and heterotypic networks in the pituitary. Taken together, these results show that the effects of Gnrh1 on Fsh release in adult female medaka are indirect and probably mediated via Lh cells.

Molecular cloning and characterization of a gonadotropin-releasing hormone receptor homolog in the Chinese mitten crab, Eriocheir sinensis

As an essential mediator in the Gonadotropin-releasing hormone (GnRH) signaling pathway, GnRH receptor (GnRHR) coupled to GnRH, plays an important role in activating the downstream pathway after stimulating a series of cascades to regulate reproduction. To detect the existence of GnRHR and potential GnRH signaling pathway, we cloned and characterized GnRHR in the Chinese mitten crab, Eriocheir sinensis (named EsGnRHR). The full-length EsGnRHR cDNA is 2038 bp in length, including an open reading frame (ORF) of 1566 bp, a 57 bp 5′-untranslated region (5′-UTR) and a 415 bp 3′-UTR. Prediction of transmembrane domains in protein sequence revealed that the EsGnRHR protein contained seven hydrophobic transmembrane regions (TMs). Reverse transcription PCR revealed that EsGnRHR was mainly expressed in the thoracic nerve group and ovary, and weakly distributed in the testis and brain. In situ hybridization further demonstrated that EsGnRHR mRNA was localized at the protocerebrum and deutocerebrum. In the ovary and testis, the hybridization signal was dominantly at the earlier developmental stages. The signal was mainly localized in the cytoplasm cell in the ovary, and in the epithelium cell in the testis. During the different stages of gonadal development, EsGnRHR displayed increasing trends in both female and male when analyzed by quantitative real-time PCR, suggesting that EsGnRHR was involved in controlling gonadal development. Our study provides important information for further research on the molecular mechanisms underlying crab development.

Changes in tissue composition in Brazilian mojarraEugerres brasilianus(Cuvier, 1830) females at different stages of gonadal development as a starting point for development of broodstock diets

Summary Thie study evaluated the changes in proximate composition and fatty acid profile in the muscle, liver and ovarian tissues of wild-caught Brazilian mojarra Eugerres brasilianus females during sexual maturation as a starting point for the development of broodstock diets. A total of 114 females captured in the Santa Cruz Canal, Itapissuma, PE, north-eastern Brazil, from August 2012 to April 2013, were classified into four stages of gonadal development by histological analyses. Ovarian protein and total lipid levels increased with maturation, and a simultaneous decrease in liver protein and lipid levels was observed. The levels of arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) also increased in the ovary as the gonadal development proceeded; they represented 96.4% of the total highly unsaturated fatty acids (HUFA) in the ovaries of fully mature females. These findings highlight the need to include protein and lipid-rich sources containing n-6 HUFA, particularly ARA, and n-3 HUFA (EPA, DPA and DHA) in the diets of Brazilian mojarra breeders.

Fatty acid and proximate composition of wild male and female king angelfish (Holacanthus passer) gonads during the ripe and spent developmental stages

Overfishing of king angelfish Holacanthus passer reduced populations in the Gulf of California. This study aimed to determine the fatty acid and proximate composition of male and female gonads, and the E2 concentration in plasma of wild organisms with different stages of gonadal development captured during early and mid-summer at El Datil, near Kino Bay, Sonora, Mexico, to help establish basic reproductive aspects and possibly to help develop the aquaculture of this ornamental species. Out of the 45 adult specimens analyzed, 66.7% were females and 33.3% were males; 16.7% of the females had ripe gonads while 83.3% had spent gonads, and 20% of males had ripe gonads while 80% had spent gonads, indicating they were reproducing earlier, likely in the spring. Females had smaller size but numerically greater gonadosomatic index (GSI) and condition factor (K) than males. Ripe and spent females showed no statistical differences in weight, length or K; however, ripe females showed significantly higher GSI (P = 0.0005) than spent females, 3.43 vs. 0.87%. Lipid content was higher in ripe gonads, with higher content of fatty acids. In both sexes, DHA was quantitatively the major fatty acid, (10.83-16.28 mg of DHA g-1 of gonad wet weight). The n-3/n-6 ratios varied from 1.99 to 3.54, lower for ripe organisms due to a higher content of ARA and n-6 derivatives. Gonad DHA content changed in relation to its developmental stage and it might serve as an additional maturation index. Information on the chemical composition and fatty acid profile of the gonads can be used as indicators of dietary lipid and essential fatty acid requirements of broodfish, which may contribute to the formulation of a balanced diet for the culture of this ornamental species.

Nutrient allocation in the gonads of the sea urchin Arbacia dufresnii in different stages of gonadal development

This study reports nutrient allocation in different stages of gonadal development for two populations of the sea urchin Arbacia dufresnii off the Patagonian coast of Argentina (Nuevo Gulf and San Jorge Gulf). The biochemical composition of gonads was used to assess nutrient allocation by measuring ash, soluble protein, lipid and trichloroacetic acid-soluble carbohydrate concentrations, and absolute contents over a 24-month period. Reproductive output in terms of energy was calculated for females. Results were correlated with histological stage of the gonads. Soluble proteins were the main component for the Nuevo Gulf population while unmeasured organic material (i.e. insoluble proteins and nucleic acids, especially in testes) was prevalent in gonads from San Jorge Gulf. Soluble protein and lipid concentrations followed the gonadal cycle, while carbohydrate concentration was almost negligible, especially in the Nuevo Gulf population. The different patterns in the gonadal cycle in the two populations were reflected in the biochemical composition of gonads. Concentrations and contents of the biochemical components and reproductive output were higher in the population from San Jorge Gulf owing to the larger size of gonads and gametes. These findings contribute to the better understanding of the plasticity of the reproductive biology of A. dufresnii in different environments.

Rapid Estimation of Gonad‐to‐Body Ratio in Eastern Oysters by Image Analysis

AbstractThe goal of this study was to develop a rapid and reliable method of quantifying the gonadal condition of eastern oysters Crassostrea virginica based on a gonad‐to‐body ratio (GBR). The objectives were to compare a previously established transect method with three alternative computer‐based image analysis (IA) methods based on acquisition time, composite GBR values, and GBR values at different stages of gonadal development. The first IA method calculated the area of the gonad and body while eliminating the dorsal and ventral curvature of the gonad, the second calculated the area of the gonad and body while eliminating the gill area, and the third calculated the total area of the gonad and body. The GBR values from the first and third IA methods were not different from those from the transect method. The second IA method resulted in higher GBR values in 80% of the measurements compared with the other three methods. However, measuring the gonadal area and total body area was five times faster than with the transect method and, excluding the curvature, was nine times faster but susceptible to visual error. Based on the speed and comparability with the transect method, the third IA method was the most useful for quantifying gonadal development.

Caloric density of Loricariichthys platymetopon (Osteichthyes, Loricariidae) in the Upper Paraná River floodplain, Brazil

This study analyzed the muscle energy content (caloric density) of L. platymetopon captured at different sites of the Upper Paraná River floodplain, and potential relationships between the content and various environmental variables (water temperature, oxygen dissolved in water, food availability, relative numeric abundance) and biological variables (body size and reproductive cycle). Quarterly samplings from September 2006 to June 2007 in the lakes and rivers resulted in a sample of 739 specimens, whose muscle caloric density was determined using a calorimeter. Differences between the caloric averages of the males and females and among the different stages of gonadal development were not significant. Caloric density varied over time and space, with two seasonal variation trends. The intensity of the correlation between the caloric density and each environmental variable, as well as the type of correlation, varied according to the sampled site. Body size and reproductive cycle were not correlated with caloric density.

Identification of multiple dmrt1s in catfish: localization, dimorphic expression pattern, changes during testicular cycle and after methyltestosterone treatment

The double sex and mab-3 related (DM) transcription factor 1 (dmrt1) plays an important role in testicular differentiation. Here, we report cloning of multiple dmrt1s, a full-length and two alternative spliced forms from adult catfish (Clarias gariepinus) testis, which encode predicted proteins of 287 (dmrt1a), 253 (dmrt1b) and 233 (dmrt1c) amino acid residues respectively. Interestingly, dmrt1c lacks the majority of the DM domain. Multiple dmrt1s (dmrt1a and dmrt1c) were obtained from Clarias batrachus as well. Tissue distribution (transcript and protein) of catfish dmrt1 revealed exclusive expression in testis. Semi-quantitative RT-PCR revealed the presence of multiple dmrt1s with high levels of dmrt1a in adult testis but not in ovary. Real-time RT-PCR analysis during testicular cycle showed higher levels of dmrt1 transcripts in preparatory and pre-spawning when compared with spawning and post-spawning phases. Immunocytochemical and immunofluorescence localization revealed the presence of catfish Dmrt1 protein in spermatogonia and spermatocytes, which indicates plausible role in spermatogenesis. Histological analysis indicated initiation of gonadal sex differentiation in catfish around 40-50 days after hatching. The potential role for dmrt1 in testicular differentiation is evident from its stage-dependent elevated expression in developing testis. Furthermore, dimorphic expressions of dmrt1s were evident at different stages of gonadal development or recrudescence in catfish. Treatment of methyl testosterone (MT) during early stages of gonadal sex differentiation resulted in adult males. Interestingly, we also obtained MT-treated fishes having ova-testis gonads. Analysis of dmrt1, sox9a, foxl2 and cyp19a1 expression patterns in MT-treated gonads revealed tissue-specific pattern. These results together suggest that multiple dmrt1s are testis-specific markers in catfish.

Molecular characterization and expression of three GnRH forms mRNA during gonad sex-change process, and effect of GnRHa on GTH subunits mRNA in the protandrous black porgy ( Acanthopagrus schlegeli)

Gonadotropin-releasing hormone (GnRH) plays a pivotal role in control of reproduction and gonadal maturation in teleost fish. To investigate the action GnRH in black porgy ( Acanthopagrus schlegeli), we examined the mRNA expression of GTH subunits (GTHα, FSHβ, and LHβ) in the pituitary as well as plasma estradiol-17β (E 2) level following treatment with a GnRH analog (GnRHa) in immature fish. The expression levels of GTH subunits mRNA and plasma E 2 level were increased after GnRHa injection. We were also able to identify three GnRH forms: salmon GnRH (sGnRH), seabream GnRH (sbGnRH) and chicken GnRH-II (cGnRH-II) by cDNA cloning in the ovary of the black porgy. Black porgy gonadal development is divided into seven stages, involving sex change from male to female (immature testis, mature testis, testicular portion of mostly testis, ovarian portion of mostly testis, testicular portion of mostly ovary, ovarian portion of mostly ovary, and mature ovary). In the present study, we investigated the expression pattern of three GnRH molecular forms in the black porgy gonads at different stages of gonadal development by quantitative polymerase chain reaction (QPCR). The mRNA expressions of sGnRH, sbGnRH and cGnRH-II were found to be higher in mature testis and ovary, compared to gonads at different stages of maturity. The findings support the hypothesis that the three forms of GnRH play important roles in the regulation of hypothalamic–pituitary–gonadal axis, and are likely involved also in gonadal development and sex change in black porgy.

Testicular involution prior to sex change in gilthead seabream is characterized by a decrease in DMRT1 gene expression and by massive leukocyte infiltration

BackgroundLeukocytes are found within the testis of most, if not all, mammals and are involved in immunological surveillance, physiological regulation and tissue remodelling. The testis of seasonal breeding fish undergoes a regression process. In the present study, the second reproductive cycle (RC) of the protandrous seasonal teleost fish, gilthead seabream, was investigated and the presence of leukocytes analysed. Special attention has been paid to the testicular degenerative process which is particularly active in the last stage of the second RC probably due to the immediacy of the sex change process.MethodsSexually mature specimens (n = 10–18 fish/month) were sampled during the second RC. Some specimens were intraperitoneally injected with bromodeoxyuridin (BrdU) before sampling. Light and electron microscopy was used to determine the different stages of gonadal development and the presence of leukocytes and PCR was used to analyse the gene expression of a testis-differentiating gene and of specific markers for macrophages and B and T lymphocytes. Immunocytochemistry and flow cytometry were performed using a specific antibody against acidophilic granulocytes from the gilthead seabream. Cell proliferation was detected by immunocytochemistry using an anti-BrdU antibody and apoptotic cells by in situ detection of DNA fragmentation.ResultsThe fish in the western Mediterranean area developed as males during the first two RCs. The testis of all the specimens during the second RC underwent a degenerative process, which started at post-spawning and was enhanced during the testicular involution stage, when vitellogenic oocytes appeared in the ovary accompanied by a progressive increase in the ovarian index. However, only 40% of specimens were females in the third RC. Leukocytes (acidophilic granulocytes, macrophages and lymphocytes) were present in the gonad and acidophilic granulocyte infiltration occurred during the last two stages. At the same time DMRT1 gene expression decreased.ConclusionsThe results demonstrate that innate and adaptive immune cells are present in the gonads of gilthead seabream. Moreover, the whole fish population underwent a testicular degenerative process prior to sex change, characterized by high rates of apoptosis and necrosis and accompanied by an infiltration of acidophilic granulocytes and a decrease in DMRT1 levels.

Ovarian development in the Amazonian red discus, Symphysodon discus Heckel (Osteichthyes: Cichlidae)

The Neotropical red discus fish, Symphysodon discus, originates from the Amazonian basin and has a discoid body. Although this species is popularly used in aquaria and is exported as an ornamental fish, it has not been intensively studied. The purpose of this work was to study the morphological and histological aspects of the ovarian development in the red discus. Forty females of S. discus of varying body sizes and different stages of gonadal development were used in this study. The ovaries were weighed and examined macroscopically in order to observe the maturation stages. Histological staining of hematoxilin-eosin was used for microscopic observations of the ovaries. Macroscopic observations showed immature, maturing, mature and partially spent stages of ovarian development. Microscopic examination of the ovaries revealed five stages and five phases of ovarian development. The ovaries of the mature females showed all the different phases of oocyte development, indicating the multiple spawning habit of this species.

Reproductive cycle of Geukensia demissa (Bivalvia: Mytilidae) on a beach at Nazaret, El Moján, Zulia State, Venezuela

The mytilid Geukensia demissa invaded Lake Maracaibo and since it is a new species at this location, little is known about its reproductive biology. We describe the reproductive cycle of this bivalve mollusk on a beach (Nazaret) located along the straight that leads into Lake Maracaibo. During 12 months (January to December), 80 specimens were collected monthly from this beach. The animals were dissected and samples of their gonadal fluid were microscopically examined to detect gametes. The different stages of gonadal development are described according to Shafee, (1989). The gonad index was calculated by the equation IG = Σ(n × V)/N. Results indicated that G. demissa presents a continuous reproductive cycle, with mature, spawning animals occurring throughout the year. Two gametogenic processes occurred, one beginning during the dry season and extending until the onset of the rainy season, and another beginning during the rainy season and extending until late November, when the animals are once again mature. Two spawning peaks were observed, one in July and the other in December; 100% spawning in the population was not observed. Synchrony was found in spawning and maturation in both male and female mussels.