Ovarian development and the reproductive profile of Astyanax altiparanae (Teleostei, Characidae) over one year: Applications in fish farming

Attempts for increasing Astyanax altiparanae spawning rates and percentage of responsive oocytes

In this study, we aimed to propose changes in the protocol of cultured Astyanax altiparanae hypophysation to increase the maximum ovulation rate of 60% registered previously. To that two consecutive experiments were conducted. In the first experiment, three carp pituitary homogenate (CPH) doses (3, 6, and 9 mg/kg) were administered in a single injection, while in the second experiment, the 6 mg/kg CPH dose was tested either in single or double injections. In the first experiment, a single injection of 3 mg/kg CPH did not induce final oocyte maturation or spawning, while a dose of 6 mg/kg CPH resulted in an increase in the plasma level of prostaglandin (PGF_2α) at ovulation. The single higher dose of 9 mg/kg CPH did not improve reproductive performance and even though anticipated the resumption of meiosis it was detrimental to the spawning rate. In the second experiment, the dose of 6 mg/kg CPH fractionated into two injections led to a higher spawning rate, spawning volume per female body mass, frequency of post-ovulatory complexes, and PGF_2α concentration at ovulation compared to the single injection. The most effective treatment remained the 6 mg/kg of CPH fractionated into two injections, but still providing very low proportion of ovulated females (∼40 %). Overall, this study indicates that the spawning protocols for this species need to be improved to induce ovulation in a larger number of females and be more potent in those females that respond positively.

New approaches concerning the testis of Astyanax lacustris (Characidae): immunohistochemical studies

Astyanax lacustris, locally known as lambari-do-rabo-amarelo, is a study model for Neotropical fish. Testis of A. lacustris shows deep morphophysiological changes throughout the annual reproductive cycle. This work analyzed the distribution of claudin-1, actin, and cytokeratin as elements of the cytoskeleton in germinal epithelium and interstitium; the distribution of type I collagen, fibronectin, and laminin as extracellular matrix compounds; and the localization of androgen receptor in the testis of this species. Claudin-1, cytokeratin, and actin were present in the Sertoli cells and modified Sertoli cells, and actin was also detected in peritubular myoid cells. Type I collagen were in the interstitial tissue, laminin in the basement membrane of germinal epithelium and endothelium, but fibronectin was additionally detected in the germinal epithelium compartment. The labeling of androgen receptor was higher in peritubular myoid cells and undifferentiated spermatogonia, and weaker labeling was detected in type B spermatogonia. Therefore, the present work highlights new aspects of the biology of the testis of A. lacustris, and contribute to amplify the understanding of this organ.

Adverse effects polystyrene microplastics exert on zebrafish heart - Molecular to individual level

In the present study the effects of sublethal concentrations of polystyrene microplastics (PS-MPs) on zebrafish were evaluated at multiple levels, related to fish activity and oxidative stress, metabolic changes and contraction parameters in the heart tissue. Zebrafish were fed for 21 days food enriched with PS-MPs (particle sizes 3-12 µm) and a battery of stress indices like DNA damage, lipid peroxidation, autophagy, ubiquitin levels, caspases activation, metabolite adjustments, frequency and force of ventricular contraction were measured in fish heart, parallel to fish swimming velocity. In particular, exposure to PS-MPs caused significant decrease in heart function and swimming competence, while enhanced levels of oxidative stress indices and metabolic adjustments were observed in the heart of challenged species. Among stress indices, DNA damage was more vulnerable to the effect of PS-MPs. Our results provide evidence on the multiplicity of the PS-MPs effects on cellular function, physiology and metabolic pathways and heart rate of adult fish and subsequent effects on fish activity and fish fitness thus enlightening MPs characterization as a potent environmental pollutant.

Factors affecting secondary sex characteristics in the yellowtail tetra, Astyanax altiparanae

This study interrogated factors which affect the appearance of secondary sexual characteristics, namely, fin spinelets (rigid dimorphic structure empirically associated with male sexual maturity in characids), in Astyanax altiparanae. Many variables such as the season of the year and several biotic components, including organism length, sex, phase of maturation, and the presence of gonads, were investigated. These factors were then associated with the physiological development of fin spinelets. The development of this trait is related to reproductive strategies but demonstrates considerable population variability as it is found throughout the year in some species but only during specific periods in others. Seventy-five specimens obtained from spontaneous spawn of farmed fish were arbitrarily grouped into small-, medium-, and large-sized groups in both summer and winter. Gonadal histology was performed to confirm each animal's sex and phase of maturation. Diaphanization of the fish was performed to visualize, count, and measure the fin spinelets. Finally, gonadectomization of some males was utilized to investigate the gonadal effect on the presence of fin spinelets. The present results show that the presence of fin spinelets is a secondary sexual characteristic of males which occurs independently of the season and is always present in males longer than 48 mm. However, in the summer, male specimens presented more rays with fin spinelets than during the winter. Furthermore, since fin spinelets were observed on immature males as well as spawning capable males, their presence cannot be directly associated with sexual maturity in male A. altiparanae, as previously supposed. Finally, gonadectomization resulted in an initial reduction in the length of fin spinelets. However, this trend was eventually normalized with time.

Reproductive cycle of the tetra Astyanax bimaculatus (Characiformes: Characidae) collected in Amazonian streams

A histological characterization of gonadal development in the tetra Astyanax bimaculatus was performed, aimed at determining its reproductive cycle in streams localized inside the Amazonian forest. Collections were carried out monthly from August 2017 to July 2018 at the Zoobotânica Foundation of Marabá, PA. Collected specimens were weighed and measured, and their gonads and liver were removed and weighed to calculate gonadosomatic and hepatosomatic indexes. Gonads were fixed and treated for routine histology for light microscopy. Materials were stained with toluidine blue and haematoxylin and eosin. The Amazonian A. bimaculatus species presented two reproductive periods in the year, one at the end of the winter season and another during the summer. Females showed an asynchronous development of their oocytes and only two reproductive phases of development were observed during the whole period 'developing' and 'spawning capable'. Males presented cystic spermatogenesis, with an anastomosing tubular testis containing spermatogonia spread along the germinal epithelium (unrestricted spermatogonial). These morphological characteristics are considered phylogenetically more primitive. Male specimens were observed to have five different phases during the period: immature, initial maturation, mid maturation, final maturation and regression. The huge fluctuations in Amazonian streams was observed, in which water volumes varied considerably across seasons, culminating even in total drought. In spite of this, A. bimaculatus could be found during all seasons, showing its impressive reproductive adaptation to its conditions.

Effects of GnRH and the dual regulatory actions of GnIH in the pituitary explants and brain slices of Astyanax altiparanae males

The pituitary gonadotropins, Fsh (follicle-stimulating hormone) and Lh (luteinizing hormone), regulate testicular development and functions in all vertebrates. At the pituitary, different signaling systems regulate the synthesis and secretion of the gonadotropins, such as the hypothalamic neuropeptides GnRH (gonadotropin-releasing hormone) and GnIH (gonadotropin-inhibitory hormone). While GnRH exerts stimulatory roles, the actions of GnIH remain controversial for many teleost species. Therefore, the aim of this study was to evaluate the in vitro effects of chicken GnRH2 (cGnRH2) and zebrafish GnIH-3 (zGnIH-3) on the male gonadotropin and GnRH system expression using pituitary explants and brain slices from a neotropical species with economical and ecological relevance, Astyanax altiparanae. Our results showed that in males, cGnRH2 increased fshb and lhb mRNA levels in the pituitary explants. Interestingly, zGnIH-3 has no effect on basal gonadotropin expression, however zGnIH-3 decreased the cGnRH2-induced fshb and lhb transcripts in male pituitary explants. In the male brain slices, zGnIH-3 showed stimulatory effects, increasing gnrh2 mRNA levels. Overall, our results suggested that GnIH seems to have dual regulatory actions on gonadotropin and GnRH2 expression of A. altiparanae males. This study provided basic information on endocrine regulation of A. altiparanae reproduction, and the obtained results will expand our knowledge, improving the reproductive management of this economically important freshwater species.

Oocyte growth, follicular complex formation and extracellular-matrix remodeling in ovarian maturation of the imperial zebra pleco fish Hypancistrus zebra

This contribution describes the growth of oocytes, addressing the formation of structures that compose the follicular complex, as well as the remodeling of the extracellular matrix, specifically laminin, fibronectin and type IV collagen during gonadal maturation. Thirty-seven females of the Acari zebra fish, Hypancistrus zebra were captured and the ovaries were submitted to histological processing for light and electron microscopy and immunohistochemistry techniques. Oogonia and four stages (I – IV) of oocytes were distinguished, and structures such as the postovulatory follicle and atretic oocytes (initial and advanced atresia) were observed. The follicular complex consists of the mature oocyte, zona radiata (Zr1, Zr2 and Zr3), follicular cells, basement membrane and theca. During oocyte growth, proteins of the extracellular matrix showed different intensities of staining. Based on these observations, a model of oocyte growth is proposed to define specific characteristics of the oocyte and the remodeling of the extracellular matrix in the ovary of H. zebra. This model of oocyte growth can be extended to other species of ornamental fishes. This study contributes data for induced fertilization and eventual conservation of this species.

Ovarian cycle in Devario aequipinnatus with emphasis on oogenesis

SummaryThis study aimed to understand how germ cell development occurs in females of Devario aequipinnatus, by morphologically describing oogenesis and the reproductive phases. Sexually mature females of D. aequipinnatus (n = 70) were obtained from commercial fisheries and delivered to the Laboratório de Ictiologia Neotropical, UNESP, Ilha Solteira, SP, Brazil. The ovaries were removed, fragmented and fixed following the usual techniques for light microscopy. The stages of ovarian development in D. aequipinnatus begin with the oogonia, which proliferate into new cells or differentiate into prophasic oocytes that, at the end of this process, form the ovarian follicle and end folliculogenesis. In the previtellogenic stage, the oocytes were characterized mainly by the gradual loss of basophilia and an increase in oocyte diameter. Vitellogenesis was marked mainly by the incorporation of yolk granules. Mature oocytes were defined by their migration from the nucleus to the micropyle. Postovulatory follicles and atresic oocytes were also observed. The reproductive phases were classified as: immature, early and final developing, spawning capable, regressing and regenerating. Therefore, the development of an understanding of cell modifications that occurs up to oogenesis is a basic step that is essential for the description of the reproductive biology of D. aequipinnatus, given the lack of information about the reproductive aspects of this species.