Expression profiling of liver in Java medaka fish exposed to 17β-estradiol

Negligible additive effect of environmental concentrations of fragmented polyethylene terephthalate microplastics on the growth and reproductive performance of Java medaka exposed to 17β-estradiol and bisphenol A

To investigate whether environmental concentrations of fragmented polyethylene terephthalate (PET) microplastics (MPs) have additional or combined effects on endocrine-disrupting activity, Java medaka (Oryzias javanicus) were exposed to 17β-estradiol (E2; 5, 10, 50, and 100 ng L-1), bisphenol A (BPA; 5, 10, 50, and 100 µg L-1), and E2 and BPA combined with PET MPs (1 and 100 particles L-1) for 200 days. The growth parameters, such as body length and weight, were significantly decreased by the highest concentrations of E2 and BPA. A significant reduction in egg production was observed in female fish exposed to BPA, with an additive toxic effect of PET MPs. A female-biased sex ratio was observed in fish exposed to both chemicals. Exposure to E2 significantly increased the hepatosomatic index (HSI) in both sexes, while no significant effect was observed in the gonadosomatic index (GSI). Exposure to BPA significantly increased the HSI in female fish and decreased the GSI in both sexes of fish. An additive effect of PET MPs was observed on the GSI value of female exposed to BPA. Significant elevations in vitellogenin (VTG) levels were observed in both sexes due to exposure to E2 and BPA. Additive effects of PET MPs were observed on VTG levels in males exposed to E2 and BPA. Taken together, even long-term treatment with PET MPs induced only a negligible additive effect on the endocrine-disrupting activity in Java medaka at environmentally relevant concentrations.

The effects of sustained and diel-cycling hypoxia on high-latitude fish Phoxinus lagowskii

High-latitude fish are subjected to sustained and diel-cycling hypoxia. Oxygen deficiency could pose a serious threat to fish, but little information is available regarding the response mechanisms employed by high-latitude fish to sustained and diel-cycling hypoxia. In this study, a combination of transcriptomics and metabolomics were used to examine the molecular response mechanisms actioned by sustained and diel-cycling hypoxia in the high-latitude fish, Phoxinus lagowskii. P. lagowskii was divided into normoxic control (6.0-7.0 mg/L dissolved oxygen), sustained (1.5 mg/L dissolved oxygen), and diel-cycling hypoxic treatment (6.0-7.0 mg/L between 07:00-21:00, and 3.0-4.0 mg/L between 21:00-07:00) tanks for 28 days. Differentially expressed genes (DEGs) and significantly different metabolites (DMs) related to digestive proteases, lipid metabolism, estrogen signaling pathway, steroid hormone biosynthesis, glutathione metabolism, and tryptophan metabolism were identified from comparative metabolomic and transcriptomic data expression profiles within the liver. The current study found that P. lagowskii had significantly different responses between sustained and diel-cycling hypoxia. P. lagowskii faced with sustained hypoxia may enhance their tolerance capacity through phospholipid and glutathione metabolism. Our data provide new insights into the high latitude fish coping with changes in hypoxia and warrants further investigation into these potentially important genes and metabolites.

The genome of the Java medaka (Oryzias javanicus): Potential for its use in marine molecular ecotoxicology

The Java medaka (Oryzias javanicus) is distributed in tropical brackish water and is considered as an ecotoxicological experimental organism for assessing diverse pollutions and global climate change effects in the ocean. In this study, we sequenced and assembled the genome of O. javanicus using the Oxford Nanopore technique and anchored the scaffolds to the 24 genetic linkage map of a sister species Oryzias melastigma. The assembled genome consisted of 773 scaffolds including 24 LG-based scaffolds, and the estimated genome length was 846.3 Mb (N50 = 19.3 Mb), containing 24,498 genes. As detoxification processes are crucial in aquatic organisms, antioxidant-related genes including glutathione S-transferases, superoxide dismutase, catalase, and glutathione peroxidase were identified in this study. In the genome of O. javanicus, a total of 21 GSTs, 4 SODs, 1 CAT, and 7 GPxs were identified and showed high similarities between sister species O. melastigma and Oryzias latipes. In addition, despite having 8 classes of cytosolic GSTs family, medaka showed no presence of GST pi and sigma classes, which are predominantly found in carp and salmon, but not in neoteleostei. This study adds another set to genome-library of Oryzias spp. and is a useful resource for better understanding of the molecular ecotoxicology.

Transcriptional changes caused by bisphenol A in Oryzias javanicus, a fish species highly adaptable to environmental salinity

The Javanese medaka, Oryzias javanicus, is a fish highly adaptable to various environmental salinities. Here, we investigated the effects of the environmental pollutant bisphenol A (BPA; an endocrine disrupting chemical) on gene expression levels in this species acclimated to different salinities. Using cDNA microarrays, we detected the induction of differential expression of genes by BPA, and compared the transcriptional changes caused by chemical exposure at different salinities. There were marked transcriptional changes induced by BPA between treatments. While 533 genes were induced by a factor of more than two when O. javanicus was exposed to BPA in seawater, only 215 genes were induced in freshwater. Among those genes, only 78 were shared and changed significantly their expression in both seawater and freshwater. Those genes were mainly involved in cellular processes and signaling pathway. We then categorized by functional group genes specifically induced by BPA exposure in seawater or freshwater. Gene expression changes were further confirmed in O. javanicus exposed to various concentrations of BPA, using quantitative real-time reverse transcription PCR based on primer sets for 28 selected genes.