This study evaluated the effect of pejerrey Odontesthes bonariensis (Valenciennes, 1835) broodstock age on gamete and spawning quality and its relationship with sex steroid plasma levels. Sperm was analysed using a computer‐assisted sperm analysis (CASA) developed for pejerrey. Semen samples were taken from all fish from mid age groups (5‐ and 7‐year fish), but it was not possible to obtain stripped semen samples from all fish of younger (3‐year) or older (10‐year) groups. The highest relative sperm weight and sperm concentration were recorded in 5‐ and 7‐year groups respectively, while viability was not different between age groups. It was not possible to identify an effect of age on sperm quality by CASA. Non‐viable spawned eggs were obtained in the 3‐year group and, the relative fecundity and the relative number of fertilized eggs decreased with age in other groups. Fertilization and hatching rates showed the highest values in the 10‐year group. However, the estimated number of hatched larvae was similar in 5‐, 7‐ and 10‐year fish. A clear effect of age on 11 ketotestosterone (11‐KT) and estradiol (E2) levels was identified, with the highest values in the 5‐ and 7‐year groups. These results might be related to the onset of puberty in the 3‐year group and ageing in the 10‐year group. Considering that the estimated number of larvae obtained was similar among age groups, the results of this study suggest that broodstock maintenance cost could be reduced by using mid‐age fish rather than older fish in pejerrey hatcheries.
17β-Estradiol (E2) and synthetic 17α-Ethinylestradiol (EE2) are estrogenic compounds present in surface waters as a consequence of municipal sewage discharges. The aim of this study was to evaluate the effects of E2, EE2 and its mixtures on different reproductive parameters and embryo-larval survival in pejerrey fish (Odontesthes bonariensis). In order to analyze the effect of these compounds on sperm quality, fertilization%, embryo-larval survival (%), and the point of no return (PNR), different assays were performed using concentrations 175, 350, 700 and 1400 ng/L of E2; 22.5, 45, 90 and 180 ng/L of EE2 and mixtures M1 (175 E2+22.5 EE2, ng/L), M2 (350 E2+45 EE2, ng/L), M3 (700 E2+90 EE2, ng/L) and M4 (1400 E2+180 EE2 ng/L). No significant differences in motility parameters were observed between E2 and EE2 treatments and the control group. However, a significant decrease in motility% was recorded for all mixtures tested compared with the control samples. For fertilization%, only sperm activated with M4 showed a significant decrease compared with the control group. In the case of embryo survival, there was only a significant decrease in the highest concentration of EE2 compared with the control group. For the mixtures, M3 is the one that had the most adverse effect on embryo survival. In larval survival, there was a significant decrease in concentration 175 and 700 ng/L of E2 compared with the control group. In EE2 treatments, the ones with a significant reduction in larval survival were concentration 45 and 90 ng/L. And for the mixture treatments, M1, M3 and M4 had a significantly lower larval survival than the control group. In comparison to other treatments, M1 demonstrated a significant difference in PNR when compared with the control group. The results obtained demonstrated that the exposure to mixtures of E2 and EE2 affected fish sperm motility, fertilization% and, embryo and larval survival even at relevant environmental concentrations highlighting the necessity of considering the effects of pollutants mixtures in ecotoxicological studies.
Some species of fish have been used as bioindicators of aquatic environmental pollution all over the world. Pejerrey (Odontesthes bonariensis) was selected for the current study due to its sensitivity to pollutants and because is one of the emblematic fish species that inhabits shallow lakes of the Pampa region (Argentina). Recently, in Chascomús lake were recorded concentrations of Cd, Cr, Cu and Zn with values above the Argentine National Guidelines for the Protection of the Aquatic life. Regarding this, the aim of the present study was to investigate the effects of environmental concentrations of these metals on the sperm quality, fertilization and hatching rates, and embryo and larval survival of pejerrey. Also, the same endpoints were analyzed with concentrations ten times higher to simulate a polluted worst-case scenario. The results showed that the presence of some metals in aquatic environments reduced pejerrey sperm motility (in~50%) and velocity (in~30%). These results were obtained using a computer assisted sperm analyzer enforcing the application of this analysis as a tool or bioindicator of aquatic pollution. In addition, fertilization rate was diminished (in~40%) for all treatments. Besides, the hatching rate, and embryo and larval survival were drastically affected being zero for the highest metal concentrations assessed. All together these results, showed that even lower metal concentrations can negatively affect different reproductive parameters of one of the most emblematic fish species of the Argentinean water bodies.
In the present study it was showed for the first time the ultrastructural morphology of O. bonariensis sperm using electron microscopy techniques. Different kinds of abnormalities were described in fresh and post thawed sperm caused by crogenic protocols. Pejerrey spermatozoon is uniflagellated and is differentiated into three parts: a small roundish head (~1.80µm in length and 1.67µm in width), a midpiece or transitional region (~1.11µm in length and 1.56µm in width), and a long tail or flagellum (~29.08µm). Samples of fresh and post thawed sperm showed evidence of morphological anomalies affecting various intracellular compartments. Spermatozoa with swollen, ruptured, or absent membranes in the head showing excess of cytoplasm, and with alteration of the spatial orientation of the mitochondria were observed. A swollen flagellum was observed containing cytoplasmic vesicles, distributed along the whole length or concentrated in a restricted part of the tail. It was also found a high level of abnormalities (60%) in frozen sperm when compared with normal sperm (18%) reflecting the damage provoked by cryopreservation procedures.No presente estudo mostrou-se pela primeira vez a morfologia estrutural dos espermatozoides de O. bonariensis utilizando técnicas de microscopia eletrônica. Diferentes tipos de anormalidades foram descritas para sêmen fresco e descongelado. O espermatozoide de Pejerrey é uniflagelado e dividido em três partes: uma cabeça pequena e arredondada (~1.80µm de comprimento e 1.67µm de largura), uma parte intermediária ou região de transição (~1.11µm de comprimento e 1.56µm de largura) e uma cauda longa ou flagelo (~29.08µm). Amostras de sêmen fresco e descongelado mostraram evidências de anormalidades morfológicas afetando vários compartimentos intracelulares. Na cabeça haviam espermatozoides com membranas dilatadas, rompidas ou ausentes, mostrando excesso de citoplasma e alteração na orientação espacial das mitocôndrias. Um flagelo dilatado foi observado contendo vesículas citoplasmáticas, as quais estavam distribuídas ao longo de todo o seu comprimento ou concentradas em uma parte restrita da cauda. Também foi encontrado um alto nível de anormalidades (60%) em sêmen congelado em comparação com o sêmen normal (18%), refletindo os danos provocados pelos procedimentos de criopreservação.
After gastrulation, oviductal hypoxia maintains turtle embryos in an arrested state prior to oviposition. Subsequent exposure to atmospheric oxygen upon oviposition initiates recommencement of embryonic development. Arrest can be artificially extended for several days after oviposition by incubation of the egg under hypoxic conditions, with development recommencing in an apparently normal fashion after subsequent exposure to normoxia. To examine the transcriptomic events associated with embryonic arrest in green sea turtles (Chelonia mydas), RNA-sequencing analysis was performed on embryos from freshly laid eggs and eggs incubated in either normoxia (oxygen tension ~159 mmHg) or hypoxia (<8 mmHg) for 36 h after oviposition (n = 5 per group). The patterns of gene expression differed markedly among the three experimental groups. Normal embryonic development in normoxia was associated with upregulation of genes involved in DNA replication, the cell cycle, and mitosis, but these genes were commonly downregulated after incubation in hypoxia. Many target genes of hypoxia inducible factors, including the gene encoding insulin-like growth factor binding protein 1 (igfbp1), were downregulated by normoxic incubation but upregulated by incubation in hypoxia. Notably, some of the transcriptomic effects of hypoxia in green turtle embryos resembled those reported to be associated with hypoxia-induced embryonic arrest in diverse taxa, including the nematode Caenorhabditis elegans and zebrafish (Danio rerio). Hypoxia-induced preovipositional embryonic arrest appears to be a unique adaptation of turtles. However, our findings accord with the proposition that the mechanisms underlying hypoxia-induced embryonic arrest per se are highly conserved across diverse taxa.
Juveniles of pejerrey, Odontesthes bonariensis, were exposed to 0.1% Alizarin Red S (ARS) alone or with a previous immersion in 2.2% saline solution (Osmotic Induction, OI) to enhance the ARS marking method. Fish were marked in the field and immediately released in 1 m 3 cages in "La Salada de Monasterio" lagoon, Chascomús, Buenos Aires, Argentina. After 73 days, clear marks were observed in the otoliths, caudal fin rays and scales with both treatments, being the intensity of the signal in the scales of OI+ARS treated fish higher. On the other hand, no marks were observed in the control group on the same structures. Approximately one year post-treatment (385 days), only marks in caudal fin rays were found clearly in OI+ARS treated fish. After this period, no significant differences in total length or weight between marked or control fish were observed and the mortality ranged between 30-40 % in all cages. These results provide strong evidence for the potential applicability of this cost-effective marking technique in differentiation of wild and hatchery-produced pejerrey. The success in the caudal fin rays marking is also important because it is easy to do and does not require the sacrifice of fish.Juvenis de pejerrey, Odontesthes bonariensis, foram expostos a Vermelho de Alizarina S (ARS) 0,1% de duas formas, sozinho ou com uma imersão anterior em 2,2% de solução salina (Indução osmótica, IO) para melhorar o método de marcação ARS. Os procedimentos foram realizados no campo e os peixes foram liberados em gaiolas (tanques-rede) de 1 m 3 na lagoa "La Salada de Monasterio", Chascomús, Buenos Aires, Argentina. Após 73 dias, marcas claras foram observadas nos otólitos, raios da nadadeira caudal e escamas em ambos os tratamentos, sendo que a intensidade do sinal nas escalas de IO + ARS de peixe tratado foi superior. Por outro lado, não foram observados marcas no grupo controle sobre as mesmas estruturas. Aproximadamente um ano pós-tratamento (385 dias), apenas marcas nos raios da nadadeira caudal foram encontrados claramente nos peixes tratados com IO+ARS. Entre os peixes observados, após este período, não houve diferenças significativas no comprimento total ou peso entre o grupo controle e marcados, ademais, a mortalidade variou entre 30-40% em todas as gaiolas. Estes resultados fornecem fortes evidências e um grande potencial para aplicação desta técnica rentável de marcação que diferencia o pejerrey selvagem e o produzido em cativeiro. O sucesso na marcação dos raios da nadadeira caudal também é de grande importância, pois sua verificação é fácil e não requer o sacrifício de peixes.
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