Short-term exposure to norethisterone affected swimming behavior and antioxidant enzyme activity of medaka larvae, and led to masculinization in the adult population

Toxic effects of anionic polyacrylamide on the developmental stages of Oryzias melastigma embryos and larvae

Anionic Polyacrylamide (APAM) is widely used in oil extraction processes, serving as an oil-repellent polymer and constituting a critical component of water-based drilling fluids. The environmental and ecological effects of APAM on fishery resources have attracted significant attention, yet its toxic mechanism in marine fish at early developmental stages remains poorly understood. The potential effects of APAM on marine medaka (Oryzias melastigma) embryos were investigated by exposing them to 0, 120, 240, 480, and 960 mg/L for 18 d. APAM exposure caused developmental toxicity in embryos, leading to reduced heart rates, delayed and decreased hatching, increased mortality and malformations. The activities of superoxide dismutase (SOD) and catalase (CAT) initially increased after 2 d of exposure but decreased after 8 and 18 days of prolonged stress, while malondialdehyde (MDA) concentration increased, causing lipid peroxidation and worsening oxidative damage. After 18 days of APAM exposure, low and medium concentrations increased the expression of cardiovascular genes GATA4 and NKX2.5, while high concentrations decreased NKX2.5, leading to heart defects like elongated hearts and pericardial cysts. Additionally, low concentrations significantly boosted nervous system genes SHHA and SYN2A, enhancing swimming behaviors, whereas high concentrations suppressed these genes, reducing swimming activity. In conclusion, this study demonstrated that APAM exposure causes developmental toxicity, oxidative stress, neurotoxicity, and disrupts early cardiac development in O. melastigma embryos, providing insight into its toxic effects on early marine fish development.

Effects of progestogen neurosteroids on locomotor activity in zebrafish embryos and larvae

The steroid hormone progesterone (P4) and related compounds called progestogens are well known for their effects on the reproductive system. However, their physiological roles outside reproduction are less understood. Additionally, there is limited information on the toxicological repercussions of environmental exposure to exogenous progestogens and how such exposure might impact the development and survival of animals living in contaminated habitats. Two progesterone-based neurosteroids, allopregnanolone and tetrahydrodeoxycorticosterone (THDOC), are known to enhance γ-aminobutyric acid type A (GABAA) receptor activity, inducing neuronal hyperpolarization. In this study, locomotor parameters in zebrafish embryos and larvae were used as endpoints to assess the inhibitory effects of pregnane neurosteroids. Specifically, spontaneous tail coiling in embryos at 24 h post-fertilization (hpf) and swimming activity in larvae aged 120-168 hpf were evaluated. Motility assays in embryos showed that P4 increased spontaneous tail coiling, whereas larvae exhibited an anesthetic-like loss of motility. This effect was both age- and dose-dependent for P4, deoxycorticosterone (DOC), 5α-dihydroprogesterone, and the membrane progesterone receptor agonist, ORG-OD-02-0, but not for other steroids tested. Removal of the steroids after the onset of anesthesia led to recovery of motility in larvae, suggesting that the observed effects are not due to a non-specific toxicity. Our results suggest that P4 targets the mPR, which acts in association with the GABAA receptor to mediate the loss of locomotor behavior. This study provides further insight into how neuroactive compounds can affect locomotor behaviors during early developmental stages in nonmammalian species.

Toxic Effects of Bisphenol AF Exposure on the Reproduction and Liver of Female Marine Medaka (Oryzias melastigma)

In recent years, bisphenol AF (BPAF) in aquatic environments has drawn attention to its ecological risks. This study aims to investigate the toxic effects of BPAF (188.33 μg/L) exposure for 30 days on female marine medaka (Oryzias melastigma). On the 10th and 30th day of exposure, the toxicity was evaluated using histological analysis of the liver and ovaries and the transcription levels of genes related to the antioxidant system, immune system, and hypothalamic-pituitary-gonadal (HPG) axis. Findings revealed that (1) BPAF exposure caused vacuolation, karyopyknosis and karyolysis in the liver of marine medaka, and the toxic impact augmented with duration; (2) exposure to BPAF for 10 days facilitated the growth and maturation of primary ova, and this exposure had a comparatively inhibitory effect after 30 days; (3) exposure to BPAF resulted in a biphasic regulation of the transcriptional abundance of genes involved in antioxidant and inflammatory response (e.g., il-8, cat), with an initial up-regulation followed by down-regulation. Additionally, it disrupted the transcriptional pattern of HPG axis-related genes (e.g., 3βhsd, arα). In conclusion, 188.33 μg/L BPAF can alter the expression levels of functionally related genes, impair the structural integrity of marine organisms, and pose a threat to their overall health.

Toxic effects of bisphenol AF on the embryonic development of marine medaka (Oryzias melastigma)

Bisphenol AF (BPAF), an emerging environmental endocrine disruptor, has been detected in surface waters worldwide and has adverse effects on aquatic organisms. The accumulation of BPAF in oceans and its potential toxic effect on marine organisms are important concerns. In this study, the effects of BPAF (10, 100, 1, and 5 mg/L) on marine medaka (Oryzias melastigma) were evaluated, including effects on the survival rate, heart rate, hatchability, morphology, and gene expression in embryos. The survival rate of marine medaka embryos was significantly lower after treatment with 5 mg/L BPAF than in the solvent control group. Exposure to 1 mg/L and 5 mg/L BPAF significantly reduced hatchability. Low-dose BPAF (10 μg/L) significantly accelerated the heart rate of embryos, while high-dose BPAF (5 mg/L) significantly decreased the heart rate. BPAF exposure also resulted in notochord curvature, pericardial edema, yolk sac cysts, cardiovascular bleeding, and caudal curvature in marine medaka. At the molecular level, BPAF exposure affected the transcript levels of genes involved in the thyroid system (dio1, dio3a, trhr2, tg, and thra), cardiovascular system (gata4, atp2a1, and cacna1da), nervous system (elavl3 and gap43), and antioxidant and inflammatory systems (sod, pparβ, and il-8) in embryos. These results indicate that BPAF exposure can alter the expression of functional genes, induce abnormal development, and reduce the hatching and survival rates in marine medaka embryos. Overall, BPAF can adversely affect the survival and development of marine medaka embryos, and BPAF may not be an ideal substitute for BPA.

Effects of bisphenols on lipid metabolism and neuro-cardiovascular toxicity in marine medaka larvae

Bisphenols are environmental endocrine disruptors that have detrimental effects on aquatic organisms. Using marine medaka larvae, this study explored the effects of bisphenol compounds [bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF), and bisphenol AF (BPAF)] on the early growth and development of aquatic organisms. Marine medaka larvae were exposed to bisphenol compounds at concentrations of 0.05, 0.5, and 5 μM for 72 h, and changes in heartbeat rate, behavior, hormone levels, and gene expression were determined. Bisphenols were shown to have a toxic effect on the cardiovascular system of larvae and can cause neurotoxicity and endocrine disruption, such as changes to thyroid-related hormones. Functional enrichment showed that bisphenols mainly affect lipid metabolism and cardiac muscle contraction of larvae, which implied that the main toxic effects of bisphenols on marine medaka larvae targeted the liver and heart. This study provides a theoretical foundation for evaluating the toxicological effects of bisphenols on the early development of aquatic organisms.

In vitro exposure to environmentally relevant concentrations of norgestrel affects sperm physiology and reproductive success of the Pacific oyster Crassostrea gigas

Progestins in aquatic environments are of increasing concern, as shown by the results of toxicological studies on adult invertebrates with external fertilization. However, their potential effects on the gametes and reproductive success of such animals remain largely unknown. Thus, the current study assessed the effect of in vitro exposure of environmentally relevant concentrations (10 ng/L and 1000 ng/L) of norgestrel (NGT) on the sperm of Pacific oyster Crassostrea gigas, analyzing sperm motility, ultrastructure, mitochondrial function, ATP status, characteristic enzyme activities, and DNA integrity underlying fertilization and hatching success. The results showed that NGT increased the percentage of motile sperm by elevating intracellular Ca²⁺ levels, Ca²⁺-ATPase activity, creatine kinase activity, and ATP content. Although superoxide dismutase activity was enhanced to eliminate reactive oxygen species generated by NGT, oxidative stress occurred, as indicated by the increase in malonaldehyde content and damage to plasma membranes and DNA. As a consequence, fertilization rates decreased. However, hatching rates did not alter significantly, possibly as a result of DNA repair processes. This study demonstrates oyster sperm as a useful, sensitive tool for toxicological research of progestins and provides ecologically relevant information on reproductive disturbance in oysters resulting from exposure to NGT.