Chronic exposure to aquacultural stressors affects pituitary-testis axis in the Mozambique tilapia Oreochromis mossambicus

Sedative and anesthetic efficacy of the essential oils from the Brazilian native plants Pilocarpus pennatifolius and Cordia verbenacea in Nile Tilapia

This study aimed to evaluate the effectiveness of essential oils (EO) of Pilocarpus pennatifolius (PPOL) and Cordia verbenacea (CVOL) as sedatives and/or anesthetics in juvenile Nile tilapia (Oreochromis niloticus). The main constituents of PPOL were 2-undecanone (57.2%) and 2-Tridecanone (28.3%), and of CVOL α-pinene (34.8%), which were determined by gas chromatography. PPOL led juveniles to sedation at concentrations of 2 (703.8s), 10 (407.4s), 20 (225.5s), 50 (190.2s), and 80 (163.5s) mg L-1. CVOL also induced sedation at these concentrations, with times of 504.9, 294.2, 142.8, 113.8, and 135.6 s, respectively. Both EOs at 200 mg L-1 induced deep anesthesia within 507.5 (PPOL) and 1267.7 s (CVOL). Exposure to PPOL at 2, 20, and 80 mg L-1 for 48 h resulted in fish sedation, while CVOL lead fish to sedation at the two lowest concentrations and anesthesia at the highest one. Possible stress responses were evaluated during anesthetic recovery and long exposure, and PPOL did not cause behavioral or glucose levels changes in all evaluations. However, CVOL increased glucose levels at the highest concentrations studied (80 and 200 mg L-1), indicating that this oil may have caused stress in fish.

Exposure to chronic stress impedes seasonal and gonadotropin-induced ovarian recrudescence in the gecko Hemidactylus frenatus

The neuroendocrine regulation of the stress-reproductive axis in reptiles is complex due to the diverse reproductive strategies adopted by these animals. Consequently, the underlying mechanisms by which stress can affect the reproductive axis remain opaque in reptiles. In the present study, we examined the effect of stress on the seasonal and FSH-induced ovarian recrudescence during the breeding and non-breeding phases of the cycle in the tropical and subtropical house gecko Hemidactylus frenatus. During the recrudescence phase of the ovarian cycle, exposure of lizards to various stressors (handling, confinement, chasing, and noise) caused a significant increase in the percentage of corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH)-immunoreactive (ir) content in the median eminence (ME) and/or pars distalis of the pituitary gland (PD), concomitant with a significant decrease in the release of gonadotropin-releasing hormone (GnRH)-ir content into the ME and PD, and number of oogonia in the germinal bed and absence of the stage IV and V (vitellogenic) follicles in the ovary compared to experimental controls. During the non-breeding phase, treatment of stressed lizards with FSH did not stimulate the development of stage IV and V follicles, in contrast to their appearance in FSH-only-treated lizards. Collectively, these findings suggest that exposure to stressors prevents the seasonal ovarian recrudescence, possibly mediated through the suppression of hypothalamic GnRH release into the ME and PD and/or directly at the level of the ovary.

Assessment of environmental exposure to betamethasone on the reproductive function of female Japanese medaka (Oryzias latipes)

Betamethasone has been extensively used in medicine in recent years and poses potential hazards to aquatic organisms. This study investigated the reproductive toxic effects of betamethasone exposure in fish, employing female Japanese medaka (Oryzias latipes) as a model. Betamethasone exposure at environmentally relevant concentrations (0, 20, 200, and 2000 ng/L) for a period of 15 weeks resulted in its high accumulation in the ovary, leading to abnormal oogenesis in female Japanese medaka. The production of gonadotropins (LH and FSH) in the pituitary gland was inhibited, and sex steroid biosynthesis in the ovary was significantly influenced at the transcriptional level. The imbalance of androgens and estrogens resulted in a decrease in the E2/T ratio and hepatic VTG synthesis, and the suppression of estrogen receptor signaling was also induced. Furthermore, betamethasone exposure delayed spawning and reduced fertility in the F0 generation, and had detrimental effects on the fertilization rate and hatchability of the F1 generation. Our results showed that environmental betamethasone had the potential to adversely affect female fertility and steroid hormone dynamics in fish.

The opioid peptide β-endorphin interferes with the pituitary-testis axis in the Mozambique tilapia Oreochromis mossambicus

Although the involvement of β-endorphin (β-ERP) in vertebrate reproduction has been suggested, its role in testicular activity is not clear in fish. We describe the influence of β-ERP on spermatogenesis in a cichlid fish in the present paper. In comparison to the control group, the administration of β-ERP (3 µg) caused a significant increase in the number of spermatogonia-A and spermatids. Following treatment with β-ERP (6 µg), a significant increase in the number of spermatogonia-A was observed, whereas the numbers of all the other germ cells, excluding spermatogonia-B, significantly decreased in comparison to those in the control group. In addition, treatment of fish with 6 µg β-ERP resulted in a significant reduction in the dimensions of the lumen and seminiferous lobules, the level of immunopositive androgen receptor (AR) expression in Sertoli cells, and the percentage of luteinizing hormone (LH) immunolabeled in the pituitary compared to those in the control group or the group treated with 3 µg β-ERP. In contrast, the intensity of AR immunoreactivity and the percentage of LH immunolabeling were substantially increased in fish treated with 3 µg β-ERP compared to those in the control group. These findings reveal for the first time that a low dose of β-ERP stimulates the recruitment of spermatogonia as well as spermateleosis, whereas a high concentration affects the recruitment of germ cells prior to meiotic division in tilapia. These results suggest that β-ERP exerts modulatory effects at the testicular and hypophysial levels through alterations in AR expression and LH secretory activity, respectively, in teleosts.

The opioid peptide leucine enkephalin modulates hypothalamic-hypophysial axis in the cichlid fish Oreochromis mossambicus

In vertebrates, opioid peptides are thought to be involved in the regulation of reproduction; however, the significance of enkephalins in testicular function remains unclear. We examined the influence of δ-opioid receptor agonist leucine enkephalin (L-ENK) on the hypophysial-testicular axis of the cichlid fish Oreochromis mossambicus. Treatment with a low dose of L-ENK (60 µg) caused a significant increase in the numbers of primary and secondary spermatocytes and early and late spermatids, concomitant with intense immunolabelling of testicular androgen receptors, but did not significantly alter serum luteinizing hormone (LH) and 11-ketotestosterone (11-KT) levels compared to those of controls. Nevertheless, treatment with a high dose of L-ENK (200 µg) caused a significant reduction in the numbers of secondary spermatocytes as well as late spermatids associated with marginal immunolabelling of androgen receptors and significantly lower concentrations of serum 11-KT and LH compared to controls. In addition, the serum cortisol level was not affected in low-dose L-ENK-treated fish, but its level was significantly increased in the high-dose L-ENK-treated group. Together, these findings indicate that a low dose of L-ENK stimulates the germ cells at the meiosis stage and promotes further stages of spermatogenesis, whereas a high concentration of L-ENK inhibits spermatogenesis at the advanced stages. This effect appears to be mediated through the suppression of testicular steroidogenesis and the reduction of LH release in the pituitary gland of tilapia. The findings also suggest that elevated L-ENK levels in teleosts may exert their inhibitory influence on the hypophysial-testicular axis via glucocorticoids.