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The longevity of sperm in teleost such as zebrafish and medaka is short when isolated even in saline-balanced solution at a physiological temperature. In contrast, some internal fertilizers exhibit the long-term storage of sperm, >10 months, in the female reproductive tract. This evidence implies that sperm in teleost possesses the ability to survive for a long time under suitable conditions; however, these conditions are not well understood. In this study, we show that the sperm of zebrafish can survive and maintain fertility in L-15-based storage medium supplemented with bovine serum albumin, fetal bovine serum, glucose, and lactic acid for 28 days at room temperature. The fertilized embryos developed to normal fertile adults. This storage medium was effective in medaka sperm stored for 7 days at room temperature. These results suggest that sperm from external fertilizer zebrafish and medaka has the ability to survive for at least 4 and 1 week, respectively, in the body fluid-like medium at a physiological temperature. This sperm storage method allows researchers to ship sperm by low-cost methods and to investigate key factors for motility and fertile ability in those sperm.

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Oryzias marmoratus and Oryzias profundicola in Lake Towuti in Sulawesi are considered to have experienced ancient admixture with a lineage phylogenetically close to the extant O. marmoratus in Lake Lantoa. However, the admixture may be ongoing because these lakes are currently connected to each other by rivers. In this study, we examined population genetic structures of O. marmoratus and O. profundicola in Lake Towuti and adjacent lakes. Mitochondrial and microsatellite analyses revealed that O. marmoratus and O. profundicola in Lake Towuti are generally clearly separated from O. marmoratus in Lake Lantoa. However, we found one O. marmoratus individual in Lake Towuti shared a mitochondrial haplotype and a large fraction of ancestry with the Lantoa O. marmoratus. The discovery of this Lantoa-type individual in Lake Towuti suggests that either dispersal of individuals from Lake Lantoa to Lake Towuti is ongoing, or that there is another unknown population within Lake Towuti that originated from ancient admixture. [ABSTRACT FROM AUTHOR]

This study aimed to explore the histomorphology of the pancreatic tissue of medaka fish to develop medaka fish as a diabetic animal model. Adult medaka fish were obtained with a body length of 2.53±0.22 cm and a weight of 265.8±25 g. Medaka fish were fixed using Boiun's fixative solution. Macro anatomical observations of the pancreas were conducted using a stereomicroscope. Histological preparations were made according to the Hematoxylin-eosin staining standard procedure. Pancreatic histomorphology of medaka fish was carried out using a light microscope with 100x and 400x magnification. The macro anatomy observations of the pancreas showed the interconnection with several tissues, such as spleen, gallbladder, liver, fat, and intestines. The pancreas was located toward the liver, oversees the intestines, and covered with fat. Pancreatic histomorphological observations showed exocrine cells composed of serous pyramidal acinar cells and endocrine cells (islets of Langerhans). Intralobular and intercalated ducts (ducts of Boll) were composed of simple cuboidal epithelium. This study concluded that the pancreas organ in medaka fish is a single organ, and histomorphologically has both of exocrine and endocrine cells.

Recent genetic and genomic studies have revealed tremendous diversity in sex chromosomes across diverse taxa. Closely related species with different sex chromosomes provide us excellent opportunities to investigate the driving forces and the consequences of sex chromosome turnover. In the present study, we investigated the diversity of sex chromosomes of 13 Oryzias species from Sulawesi, Indonesia, which diversified during the last 4.86 million years. Using pooled sequencing, we found sex chromosomes in nine species that all had XY systems, with a species being possibly modified by multiple loci. Seven species (O. woworae, O. asinua, O. wolasi, O. matanensis, O. celebensis, O. hadiatyae, and O. dopingdopingensis) share linkage group (LG) 24 as sex chromosomes; however, they differed in the length and magnitude of sequence divergence between the X and Y chromosomes. The sex chromosome of O. eversi was LG4, which has not been reported as a sex chromosome in any other medaka species. In O. sarasinorum, LG16 and LG22 are associated with sex. Although LG16 was found to be sex‐linked in another medaka species previously examined, the sex‐determining regions did not overlap. No significant signatures for sex chromosomes were identified in the other four species (O. marmoratus, O. nigrimas, O. nebulosus, and O. orthognathus). Frequent turnovers and the great diversity of the sex chromosomes will make Sulawesian medaka species a model system for investigating the driving forces and consequences of sex chromosome turnover. [ABSTRACT FROM AUTHOR]

Oryzias is a genus of rice fish belonging to the family Adrianichthyidae (Class Actinopterygii, Order: Beloniformes), usually found in estuarine and freshwater areas. So far, only two species are recorded from West Bengal under this genus viz., Oryzias dancena (Hamilton 1822) and Oryzias melastigma (McClelland 1839). Present work reports the first record of Oryzias carnaticus (Jerdon 1849), from West Bengal. The species was collected from the mangrove ecosystem of Sunderban Biosphere Reserve. Details of the morphological data, live coloration and wild habitat are provided for the new record. [ABSTRACT FROM AUTHOR]

The intensity of oxygen consumption and the rate of phosphorus excretion are studied in planktonic crustaceans Daphnia longispina O.F. Müller (Cladocera), benthic crustaceans Hyalella azteca (Saussure) (Amphipoda), and fish Oryzias latipes (Temminck & Schlegel) (Beloniformes) united in one trophic net in an experimental ecosystem. The highest rates of metabolic intensity are established for small organisms Daphnia longispina (7.44 ± 2.49 mgO/(g h) and 0.447 ± 0.143 mgP/(g h)). The rate of phosphorus excretion differed by an order of magnitude between hydrobionts of different ecological groups and decreased in the order planktonic crustaceans –> benthic crustaceans –> fish. It is shown that the contribution of hydrobionts to the creation of primary production depends on the biomass of a particular species. [ABSTRACT FROM AUTHOR]

Recently, nano-titanium dioxide (nano-TiO 2 ) has been widely distributed over surface water. However, there are few reports on its effects on the central nervous system of fish. In this study, we investigated whether nano-TiO 2 enters the medaka brain after exposure and its effect on the brain. Marine medaka brains were examined after exposure to 0.01 g/L nano-TiO 2 for 3, 10, and 20 d. Nano-TiO 2 -like particles were found in the telencephalon of treated fish. There was no obvious brain histopathological injury. The number of irregular mitochondria with absent cristae increased. Gene expression of the apoptosis-related genes, casp8, bcl2b, and bax, decreased significantly in the nano-TiO 2 group at 3 d. In contrast, the pyroptosis-related genes, gsdmeb and casp1, and inflammation-related factor, il18, increased significantly. As an activated microglia marker, mRNA expression of cd68 increased significantly in the nano-TiO 2 treated group. Moreover, CD68 protein expression also increased significantly at 10 d. Altogether, we show that nano-TiO 2 can alter mitochondrial morphology in the telencephalon of medaka, leading to microglial activation and pyroptosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The impact of leachates from micronized beached plastics of the Mediterranean Sea and Atlantic Ocean on coastal marine ecosystems was investigated by using a multidisciplinary approach. Chemical analysis and ecotoxicological tests on phylogenetically distant species were performed on leachates from the following plastic categories: bottles, pellets, hard plastic (HP) containers, fishing nets (FN) and rapido trawling rubber (RTR). The bacteria Alivibrio fischeri, the nauplii of the crustaceans Amphibalanus amphitrite and Acartia tonsa, the rotifer Brachionus plicatilis, the embryos of the sea urchin Paracentrotus lividus, the ephyrae of the jellyfish Aurelia sp. and the larvae of the medaka Oryzias latipes were exposed to different concentrations of leachates to evaluate lethal and sub-lethal effects. Thirty-one additives were identified in the plastic leachates; benzophenone, benzyl butyl phthalate and ethylparaben were present in all leachates. Ecotoxicity of leachates varied among plastic categories and areas, being RTR, HP and FN more toxic than plastic bottles and pellets to several marine invertebrates. The ecotoxicological results based on 13 endpoints were elaborated within a quantitative weight of evidence (WOE) model, providing a synthetic hazard index for each data typology, before their integrations in an environmental risk index. The WOE assigned a moderate and slight hazard to organisms exposed to leachates of FN and HP collected in the Mediterranean Sea respectively, and a moderate hazard to leachates of HP from the Atlantic Ocean. No hazard was found for pellet, bottles and RTR. These findings suggest that an integrated approach based on WOE on a large set of bioassays is recommended to get a more reliable assessment of the ecotoxicity of beached-plastic leachates. In addition, the additives leached from FN and HP should be further investigated to reduce high concentrations and additive types that could impact marine ecosystem health., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants generally found in complex mixtures. PAHs are known to cause pleiotropic effects on living organisms, including developmental defects, mutagenicity, carcinogenicity and immunotoxicity, and endocrine disruptions. The main goal of this study is to evaluate the toxicity of water-accommodated fractions (WAFs) of oils in two life stages of the Japanese medaka, larvae and juveniles. The deleterious effects of an acute exposure of 48 h to two WAFs from Arabian light crude oil (LO) and refined oil from Erika (HO) were analyzed in both stages. Relevant endpoints, including ethoxy resorufin-O-deethylase (EROD) activity, DNA damage (Comet assay), photomotor response, and sensitivity to nervous necrosis virus (NNV) infection, were investigated. Larvae exposed to both oil WAFs displayed a significant induction of EROD activity, DNA damage, and developmental anomalies, but no behavioral changes. Deleterious effects were significantly increased following exposure to 1 and 10 μg/L of LO WAFs and 10 μg/L of HO WAFs. Larval infection to NNV induced fish mortality and sharply reduced reaction to light stimulation. Co-exposure to WAFs and NNV increased the mortality rate, suggesting an impact of WAFs on fish defense capacities. WAF toxicity on juveniles was only observed following the NNV challenge, with a higher sensitivity to HO WAFs than to LO WAFs. This study highlighted that environmentally realistic exposure to oil WAFs containing different compositions and concentrations of oil generated high adverse effects, especially in the larval stage. This kind of multi-marker approach is particularly relevant to characterize the toxicity fingerprint of environmental mixtures of hydrocarbons and PAHs., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In the modern era, chemicals and their products have been used everywhere like agriculture, healthcare, food, cosmetics, pharmaceuticals, household products, clothing industry, etc. These chemicals find their way to reach the aquatic ecosystem (directly/indirectly) and cause severe chronic and prolonged toxic effects to aquatic species which is also then translated to human beings. Prolonged and chronic toxicity data of many chemicals that are used daily is not available due to high experimentation testing costs, time investment, and the requirement of a large number of animal sacrifices. Thus, in silico approaches (e.g., QSAR (quantitative structure-activity relationship)) are the best alternative for chronic and prolonged toxicity predictions. The present work offers multi-endpoint (five endpoints: chronic_LOEC, prolonged_14D_LC 50 , prolonged_14D_NOEC, prolonged_21D_LC 50 , prolonged_21D_NOEC) QSAR models for addressing the prolonged and chronic aquatic toxicity of chemicals toward fish (O. latipes). The statistical results (R 2 =0.738-0.869, Q LOO 2 =0.712-0.831, Q (F1) 2 =0.618-0.731) of the developed models show that they were robust, reliable, reproducible, accurate, and predictive. Some of the features that are responsible for prolonged and chronic toxicity of chemicals towards O. latipes are as follows: the presence of substituted benzene, hydrophobicity, unsaturation, electronegativity, the presence of long-chain fragments, the presence of a greater number of atoms at conjugation, and the presence of halogen atoms. On the other hand, hydrophilicity and graph density descriptors retard the aquatic chronic and prolonged toxicity of chemicals toward O. latipes. The PPDB (pesticide properties database) and experimental and investigational classes of drugs from the DrugBank database were also screened using the developed model. Thus, these multi-endpoint models will be helpful for data-gap filling and provide a broad range of applicability. Therefore, this research will aid in the in silico QSAR (quantitative structure-activity relationship) prediction (non-animal testing) of the prolonged and chronic toxicity of untested and new toxic chemicals/drugs/pesticides, design and development of eco-friendly, novel, and safer chemicals, and help to protect the aquatic ecosystem from exposure to toxic and hazardous chemicals., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Multi-photon 3D laser printing has gathered much attention in recent years as a means of manufacturing biocompatible scaffolds that can modify and guide cellular behavior in vitro. However, in vivo tissue engineering efforts have been limited so far to the implantation of beforehand 3D printed biocompatible scaffolds and in vivo bioprinting of tissue constructs from bioinks containing cells, biomolecules, and printable hydrogel formulations. Thus, a comprehensive 3D laser printing platform for in vivo and in situ manufacturing of microimplants raised from synthetic polymer-based inks is currently missing. Here, a platform for minimal-invasive manufacturing of microimplants directly in the organism is presented by one-photon photopolymerization and multi-photon 3D laser printing. Employing a commercially available elastomeric ink giving rise to biocompatible synthetic polymer-based microimplants, first applicational examples of biological responses to in situ printed microimplants are demonstrated in the teleost fish Oryzias latipes and in embryos of the fruit fly Drosophila melanogaster. This provides a framework for future studies addressing the suitability of inks for in vivo 3D manufacturing. The platform bears great potential for the direct engineering of the intricate microarchitectures in a variety of tissues in model organisms and beyond., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Naphthenic acids (NAs) are important pollutants in marine crude oils and have obvious toxic effects on marine organisms. However, the effects of NAs on the intestine are largely unknown. Thus, we evaluated the effects of NAs exposure in the intestines of marine medaka. Fish were experimentally exposed to NAs (0.5 mg/L, 5 mg/L, and 10 mg/L) for 96 h and monitored for changes in intestinal histology, markers of oxidative stress, and intestinal microbiome responses. Significant mucosal damage, inflammation, and oxidative stress were observed in the intestines of marine medaka after exposure to NAs. In addition, significant changes in the gut microbiota were observed. Specifically, the relative abundance of Proteobacteria decreased, while that of Verrucomicrobiota increased in the high-concentration exposure group. In addition, nutrient synthesis and metabolism in the gut were affected. The results of this study contribute to a better understanding of the ecological risk of different concentrations of NAs to marine organisms. CAPSULE ABSTRACT: Changes in the gut microbial community of marine medaka (Oryzias melastigma) caused by naphthenic acids in the marine environment were investigated through the assessment of gut inflammatory factors and comprehensive analysis using 16S rDNA high-throughput sequencing. The results indicated the induction of intestinal inflammation and changes in the structural composition of the intestinal flora., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Abstract Background Pelvic brooding is a form of uni-parental care, and likely evolved in parallel in two lineages of Sulawesi ricefishes. Contrary to all other ricefishes, females of pelvic brooding species do not deposit eggs at a substrate (transfer brooding), but carry them until the fry hatches. We assume that modifications reducing the costs of egg carrying are beneficial for pelvic brooding females, but likely disadvantageous in conspecific males, which might be resolved by the evolution of sexual dimorphism via sexual antagonistic selection. Thus we hypothesize that the evolution of pelvic brooding gave rise to female-specific skeletal adaptations that are shared by both pelvic brooding lineages, but are absent in conspecific males and transfer brooding species. To tackle this, we combine 3D-imaging and morphometrics to analyze skeletal adaptations to pelvic brooding. Results The morphology of skeletal traits correlated with sex and brooding strategy across seven ricefish species. Pelvic brooding females have short ribs caudal of the pelvic girdle forming a ventral concavity and clearly elongated and thickened pelvic fins compared to both sexes of transfer brooding species. The ventral concavity limits the body cavity volume in female pelvic brooders. Thus body volumes are smaller compared to males in pelvic brooding species, a pattern sharply contrasted by transfer brooding species. Conclusions We showed in a comparative framework that highly similar, sexually dimorphic traits evolved in parallel in both lineages of pelvic brooding ricefish species. Key traits, present in all pelvic brooding females, were absent or much less pronounced in conspecific males and both sexes of transfer brooding species, indicating that they are non-beneficial or even maladaptive for ricefishes not providing extended care. We assume that the combination of ventral concavity and robust, elongated fins reduces drag of brooding females and provides protection and stability to the egg cluster. Thus ricefishes are one of the rare examples where environmental factors rather than sexual selection shaped the evolution of sexually dimorphic skeletal adaptations.

Pesticides in urban runoff are a major source of pollutants in aquatic ecosystems. Fipronil, a phenylpyrazole insecticide, found in structural pest control products, turf grass control, and home pet flea medication, has recently increased in use and is commonly detected in urban runoff. However, little is known about the effects of fipronil on aquatic organisms at early developmental stages. Here, we evaluated toxicity of fipronil to embryos of Japanese Medaka (Oryzias latipes, Qurt strain) using a high-throughput 96-well plate toxicity test. Male and female embryos (

Dioxins and the emerging dioxin-like compounds (DLCs) have recruited increasing concerns about their environmental contamination, toxicity, health impacts, and mechanisms. Based on the structural similarity of dioxins and many DLCs, their toxicity was predominantly mediated by the dioxin receptor (aryl hydrocarbon receptor, AHR) in animals (including human), which can be different in expression and function among species and then possibly produce the species-specific risk or toxicity. To date, characterizing the AHR of additional species other than human and rodents can increase the accuracy of toxicity/risk evaluation and increase knowledge about AHR biology. As a key model, the medaka AHR has not been clearly characterized. Through genome survey and phylogenetic analysis, we identified four AHRs (olaAHR1a, olaAHR1b, olaAHR2a, and olaAHR2b) and two ARNTs (olaARNT1 and olaARNT2). The medaka AHR pathway was conserved in expression in nine tested tissues, of which olaAHR2a represented the predominant subform with greater abundance. Medaka AHRs and ARNTs were functional and could be efficiently transactivated by the classical dioxin congener 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), although olaAHR1a did not seem to cooperate with olaARNT2. In terms of function/sensitivity, the EC 50 values of medaka olaAHR1a (9.01 ± 1.43 nM), olaAHR1b (4.00 ± 1.10 nM), olaAHR2a (8.75 ± 3.34 nM), and olaAHR2b (3.06 ± 0.81 nM) showed slight differences; however, they were all at the nM level. The sensitivity of four medaka AHRs to TCDD was similar to that of zebrafish dreAHR2 (the dominant form, EC 50  = 3.14 ± 4.19 nM), but these medaka AHRs were more sensitive than zebrafish dreAHR1b (EC 50  = 27.05 ± 18.51 nM). The additional comparison also indicated that the EC 50 values in various species were usually within the nM range, but AHRs of certain subforms/species can vary by one or two orders of magnitude. In summary, the present study will enhance the understanding of AHR and help improve research on the ecotoxicity of dioxins/DLCs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Telomerase is an RNA-protein complex that includes a unique reverse transcriptase that catalyzes the addition of single-stranded telomere DNA repeats onto the 3' ends of linear chromosomes using an integral telomerase RNA (TR) template. Vertebrate TR contains the template/pseudoknot (t/PK) and CR4/5 domains required for telomerase activity in vitro. All vertebrate pseudoknots include two subdomains: P2ab (helices P2a and P2b with a 5/6-nt internal loop) and the minimal pseudoknot (P2b-P3 and associated loops). A helical extension of P2a, P2a.1, is specific to mammalian TR. Using NMR, we investigated the structures of the full-length TR pseudoknot and isolated subdomains in Oryzias latipes (Japanese medaka fish), which has the smallest vertebrate TR identified to date. We determined the solution NMR structure and studied the dynamics of medaka P2ab, and identified all base pairs and tertiary interactions in the minimal pseudoknot. Despite differences in length and sequence, the structure of medaka P2ab is more similar to human P2ab than predicted, and the medaka minimal pseudoknot has the same tertiary interactions as the human pseudoknot. Significantly, although P2a.1 is not predicted to form in teleost fish, we find that it forms in the full-length pseudoknot via an unexpected hairpin. Model structures of the subdomains are combined to generate a model of t/PK. These results provide evidence that the architecture for the vertebrate t/PK is conserved from teleost fish to human. The organization of the t/PK on telomerase reverse transcriptase for medaka and human is modeled based on the cryoEM structure of Tetrahymena telomerase, providing insight into function.

Anthropogenic disturbance of seleniferous soils can lead to selenium contamination of waterways. Although selenium is an essential micronutrient, bioaccumulation and maternal transfer of proteinaceous selenomethionine (SeMet) can result in embryo toxicity. Furthermore, as the climate changes, the salinity of spawning grounds in water-restrained estuaries is increasing. Although a small increase in salinity may not directly impact adult fish, it may alter the detoxification strategies of developing organisms. Previous research indicates that hypersalinity may potentiate SeMet embryo toxicity at an early developmental stage. However, embryonic development is a complex, spatiotemporal process with a constantly shifting cellular microenvironment. To generate thresholds and an adverse outcome pathway for the interactions between selenium and salinity, we sought to identify windows of susceptibility for lethality and deformities in the Japanese medaka (Oryzias latipes). Embryos were treated in freshwater or saltwater for 24 h with 0.5 µM, 5 µM, and 50 µM SeMet at 6 different developmental stages (9, 17, 25, 29, 34, and 38). Survival, hatch, deformities (total, type, and severity), and days to hatch were quantified. Selenium embryo tissue measurements were performed. Selenomethionine exposures of 5 µM and 50 µM significantly decreased survival and hatch at all stages. However, SeMet uptake was stage-dependent and increased with stage. Stage 17 (early neurulation) was identified as the most susceptible stage for lethality and deformities. Selenomethionine in saltwater caused significantly greater toxicity than freshwater at stage 25 (early organogenesis), suggesting a role for liver and osmoregulatory organogenesis in toxicity.

An increasing volume of empirical studies demonstrated that hybridization between distant lineages may have promoted speciation in various taxa. However, the timing, extent and direction of introgressive hybridization remain unknown in many cases. Here, we report a possible case in which repeated hybridization promoted divergence of Oryzias ricefishes (Adrianichthyidae) on Sulawesi, an island of Wallacea. Four Oryzias species are endemic to the Malili Lake system in central Sulawesi, which is composed of five tectonic lakes; of these, one lake is inhabited by two species. Morphological and population genomic analyses of genome‐wide single‐nucleotide polymorphisms revealed that these two sympatric species are phylogenetically sister to but substantially reproductively isolated from each other. Analyses of admixture and comparison of demographic models revealed that the two sympatric species experienced several substantial introgressions from outgroup populations that probably occurred soon after they had secondary contact with each other in the lake. However, the ratio of migrants from the outgroups was estimated to be different between the two species, which is consistent with the hypothesis that these introgressions aided their divergence or prevented them from forming a hybrid swarm. Repeated lake fragmentations and fusions may have promoted diversification of this freshwater fish species complex that is endemic to this ancient lake system. [ABSTRACT FROM AUTHOR]

Quantum dots, which won the Nobel Prize in Chemistry, have recently gained significant attention in precision medicine due to their unique properties, such as size-tunable emission, high photostability, efficient light absorption, and vibrant luminescence. Consequently, there is a growing demand to identify new types of quantum dots from various sources and explore their potential applications as stimuli-responsive biosensors, biomolecular imaging probes, and targeted drug delivery agents. Biomass-waste-derived carbon quantum dots (CQDs) are an attractive alternative to conventional QDs, which often require expensive and toxic precursors, as they offer several merits in eco-friendly synthesis, preparation from renewable sources, and cost-effective production. In this study, we evaluated three CQDs derived from biomass waste for their potential application as non-toxic bioimaging agents in various cell lines, including human dermal fibroblasts, HeLa, cardiomyocytes, induced pluripotent stem cells, and an in-vivo medaka fish (Oryzias latipes) model. Confocal microscopic studies revealed that CQDs could assist in visualizing inflammatory processes in the cells, as they were taken up more by cells treated with tumor necrosis factor-α than untreated cells. In addition, our quantitative real-time PCR gene expression analysis has revealed that citric acid-based CQDs can potentially reduce inflammatory markers such as Interleukin-6. Our studies suggest that CQDs have potential as theragnostic agents, which can simultaneously identify and modulate inflammatory markers and may lead to targeted therapy for immune system-associated diseases., (© 2024. The Author(s).)

Bisphenol AF (BPAF) is a novel environmental endocrine disruptor, and is widely detected in the aquatic environment, which is a potential threat to the health of fish. In this study, male Oryzias curvinotus were exposed to environmental concentrations (0.93 and 9.33 μg/L) of BPAF for 21 days. The effects of BPAF on survival, growth, reproduction, liver and testis histology, and gene transcriptional profiles of O. curvinotus were investigated. The results showed that the survival rate of male O. curvinotus slight decrease with increasing BPAF concentration, and there was no significant effect on body length, body weight, and K-factor. BPAF (9.33 μg/L) caused significant changes in testicular structure and reduced spermatid count in O. curvinotus. Changes in transcript levels of some antioxidant-related genes in gills and liver following BPAF exposure, imply an effect of BPAF on the immune system. After BPAF exposure, chgs and vtgs were up-regulated, validating the estrogenic effect of BPAF. In the hypothalamic - pituitary - gonadal axis (HPG) results, erα, erγ and cyp19a1b were all up-regulated in the brain, and the 0.93 μg/L BPAF group was more up-regulated than the 9.33 μg/L BPAF group. In testis, BPAF significantly up-regulated the mRNA expression level of cyp17a1 and cyp11b, while significantly down-regulated mRNA expression level of cyp11a, and cyp19a1 was significantly down-regulated only in the 0.93 μg/L BPAF group. In conclusion, environmental levels of BPAF have adverse effects on the survival and reproduction of O. curvinotus, and the potential toxic effects of environmental levels of BPAF cannot be ignored., Competing Interests: Declaration of competing interest The authors have no relevant financial or non-financial interests to disclose., (Copyright © 2024 Elsevier Inc. All rights reserved.)

There is global concern that microplastics may harm aquatic life. Here, we examined the effects of fine polystyrene microplastics (PS-MPs, 2-μm diameter, 0.1 mg/L, 2.5 × 10 7 particles/L) on the behavior and the microbiome (linked to brain-gut interaction) of a fish model using medaka, Oryzias latipes. We found that shoaling behavior was reduced in PS-MP-exposed medaka compared with control fish during the exposure period, but it recovered during a depuration period. There was no difference in swimming speed between the PS-MP-exposed and control groups during the exposure period. Analysis of the dominant bacterial population (those comprising ≥1% of the total bacterial population) in the gut of fish showed that exposure to PS-MPs tended to increase the relative abundance of the phylum Fusobacteria and the genus Vibrio. Furthermore, structural-equation modeling of gut bacteria on the basis of machine-learning data estimated strong relationship involved in the reduction of the functional bacterial species of minority (<1% of the total bacterial population) such as the genera Muribaculum (an undefined role), Aquaspirillum (a candidate for nitrate metabolism and magnetotactics), and Clostridium and Phascolarctobacterium (potential producers of short-chain fatty acids, influencing behavior by affecting levels of neurotransmitters) as a group of gut bacteria in association with PS-MP exposure. Our results suggest that fish exposure to fine microplastics may cause dysbiosis and ultimately cause social behavior disorders linked to brain-gut interactions. This effect could be connected to reduction of fish fitness in the ecosystem and reduced fish survival., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Generally, in vertebrates, the first step toward fertilization is the ovulation of mature oocytes, followed by their binding to sperm cells outside of the ovary. Exceptionally, the oocytes of poeciliid fish are fertilized by sperm cells within the follicle, and the developmental embryo is subsequently released into the ovarian lumen before delivery. In the present study, we aimed to identify the factor(s) responsible for intrafollicular fertilization in a viviparous teleost species, Poecilia reticulata (guppy). Sperm tracking analysis in this regard indicated that in this species, sperm cells reached immature oocytes including the germinal vesicle, and the insemination assay indicated that the immature oocytes robustly adhered to the sperm cells; similar binding was not observed in Danio rerio (zebrafish) and Oryzias latipes (medaka). We also identified the Ly6/uPAR protein bouncer as the factor responsible for the observed sperm binding activity of the immature oocytes in this species. The recombinant bouncer peptide acted as an inhibitory decoy for the sperm-oocyte binding in guppy. On the other hand, ectopic expression of guppy bouncer in zebrafish oocytes resulted in interspecific sperm-oocyte binding. These results argue that bouncer is responsible for sperm-immature oocyte binding. Our findings highlight the unique reproductive strategies of guppy fish and enhance our understanding of the diverse reproductive mechanisms in vertebrates., (© 2024 Japanese Society of Developmental Biologists.)

Sympatric speciation is considered to be difficult without the coupling between ecological traits that allow resource partitioning and reproductive traits that allow assortative mating. Such "magic traits" are known to be involved in most of the compelling examples of sympatric speciation. In this study, we report a possible case of sympatric speciation without magic traits. Three species of ricefish (genus Oryzias) are suggested to have diverged sympatrically within Lake Poso, an ancient lake in Sulawesi. An analysis of genome‐wide single‐nucleotide polymorphisms showed that these three species are reproductively isolated from each other throughout the lake. Stable isotope analyses revealed that the three species use different food resources, which reflect differences in their feeding morphologies (gill rakers and digestive tracts) and feeding sites. Field and laboratory observations showed that O. nebulosus and O. orthognathus share a mating habitat of cobbles, where they scatter fertilized eggs, whereas this site is never used by O. nigrimas, indicating that assortative mating is partly achieved by spatial isolation. The small, less‐adhesive eggs of O. nebulosus and O. orthognathus probably reflect their adaptation to spawning on cobble beaches. Laboratory mating experiments showed strong prezygotic isolation between O. nebulosus and O. orthognathus, which is achieved by strong species recognition presumably by both sexes based on species‐specific mating dances and nuptial coloration. In summary, the assortative mating of O. nebulosus and O. orthognathus is probably not coupled to resource partitioning. We discussed how sympatric speciation among these species might have been achieved even without magic traits. [ABSTRACT FROM AUTHOR]

Fish embryos are widely used as models in toxicology, drug development, and human disease research because of their high sensitivity, observability, and operability, providing the basis for an in-depth understanding of the embryogenesis. Increasing studies have indicated that birth defects are hereditary. In this study, we used Oryzias melastigma as a model to conduct a study of 185-day embryogenesis and observed self-induced non-pathological abnormal embryogenesis. O. melastigma experienced pre-puberty stage, adolescence stage, and senescence stage, and individuals produced up to 102 eggs per day. However, the fecundity was markedly reduced during the senescent stage. During the active egg and blastodisc stages, pseudo-fertilization and pseudo-blastocysts were observed. During cleavage at the 4- to 32-cell stages, we observed blastomeres separation or dislocation. Excessively separated blastomeres formed double blastoderms, eventually resulting in conjoined twins. During the blastula stage, we observed abnormally increased cell volume, narrowed and elongated blastocysts, and abnormally coated blastoderms. At the organogenesis stage, we observed abnormal numbers of Kupffer's vesicles and conjoined twins. Abnormality in the location and number of oil droplets were observed in various development stages. Abnormal development was more commonly observed in fertilized eggs produced by broodstock in prepuberty or senescence stages, which is probably related to the age of fish and the egg quality. This study can provide the materials for comparative analysis in toxicological and molecular studies of O. melastigma, and may provide evidence for other economic fish that produce sticky eggs. [ABSTRACT FROM AUTHOR]

Background: Pelvic brooding is a form of uni-parental care, and likely evolved in parallel in two lineages of Sulawesi ricefishes. Contrary to all other ricefishes, females of pelvic brooding species do not deposit eggs at a substrate (transfer brooding), but carry them until the fry hatches. We assume that modifications reducing the costs of egg carrying are beneficial for pelvic brooding females, but likely disadvantageous in conspecific males, which might be resolved by the evolution of sexual dimorphism via sexual antagonistic selection. Thus we hypothesize that the evolution of pelvic brooding gave rise to female-specific skeletal adaptations that are shared by both pelvic brooding lineages, but are absent in conspecific males and transfer brooding species. To tackle this, we combine 3D-imaging and morphometrics to analyze skeletal adaptations to pelvic brooding. Results: The morphology of skeletal traits correlated with sex and brooding strategy across seven ricefish species. Pelvic brooding females have short ribs caudal of the pelvic girdle forming a ventral concavity and clearly elongated and thickened pelvic fins compared to both sexes of transfer brooding species. The ventral concavity limits the body cavity volume in female pelvic brooders. Thus body volumes are smaller compared to males in pelvic brooding species, a pattern sharply contrasted by transfer brooding species. Conclusions: We showed in a comparative framework that highly similar, sexually dimorphic traits evolved in parallel in both lineages of pelvic brooding ricefish species. Key traits, present in all pelvic brooding females, were absent or much less pronounced in conspecific males and both sexes of transfer brooding species, indicating that they are nonbeneficial or even maladaptive for ricefishes not providing extended care. We assume that the combination of ventral concavity and robust, elongated fins reduces drag of brooding females and provides protection and stability to the egg cluster. Thus ricefishes are one of the rare examples where environmental factors rather than sexual selection shaped the evolution of sexually dimorphic skeletal adaptations. [ABSTRACT FROM AUTHOR]

Selenium (Se) is an essential micronutrient that can cause embryotoxicty at levels 7-30 times above essential concentrations. Exposure to hypersaline conditions and 50 μM selenomethionine (SeMet) decreased embryo hatch and depleted glutathione in Japanese medaka embryos without affecting Se accumulation. To better understand the impacts of nonchemical stressors on developmental toxicity of Se in fish, several adverse outcome pathways were evaluated in the Japanese medaka (Oryzias latipes). We treated medaka embryos at 12 h post fertilization with 50 μM SeMet for 12 hours in freshwater or in 13 ppth hypersalinity and evaluated the contributions of oxidative stress, the unfolded protein response and apoptosis to reduced hatch. Exposure to SeMet and hypersalinity decreased embryo hatch to 3.7% ± 1.95, and induced teratogenesis in 100% ± 0 of hatched embryos. In contrast, treatments of freshwater, saltwater, and SeMet in freshwater resulted in 89.8% ± 3.91-86.7% ± 3.87 hatch, and no significant increase in deformities. We found no significant differences in lipid peroxidation, indicating that oxidative stress may not be responsible for the observed toxicity in embryos at this time point (24 h). Although significant changes in apoptosis were not observed, we witnessed up to 100 fold increases in transcripts of the endoplasmic reticulum (ER) chaperone, immunoglobulin binding protein (BiP) and trends toward increasing downstream signals, activating transcription factor 4 (ATF4) and ATF6 indicating potential contributions of the unfolded protein response to the effects of SeMet and hypersaline conditions. These data indicate that multiple adverse outcome pathways may be responsible for the developmental toxicity of Se and salinity, and these pathways may be time dependent.

Telomerase is a unique reverse transcriptase that maintains the 3' ends of eukaryotic chromosomes by adding tandem telomeric repeats. The RNA subunit (TR) of vertebrate telomerase provides a template for reverse transcription, contained within the conserved template/pseudoknot domain, and a conserved regions 4 and 5 (CR4/5) domain, all essential for catalytic activity. We report the nuclear magnetic resonance (NMR) solution structure of the full-length CR4/5 domain from the teleost fish medaka (Oryzias latipes). Three helices emanate from a structured internal loop, forming a Y-shaped structure, where helix P6 stacks on P5 and helix P6.1 points away from P6. The relative orientations of the three helices are Mg2+ dependent and dynamic. Although the three-way junction is structured and has unexpected base pairs, telomerase activity assays with nucleotide substitutions and deletions in CR4/5 indicate that none of these are essential for activity. The results suggest that the junction is likely to change conformation in complex with telomerase reverse transcriptase and that it provides a flexible scaffold that allows P6 and P6.1 to correctly fold and interact with telomerase reverse transcriptase.

Abstract Although there are many examples of color evolution potentially driven by sensory drive, only few studies have examined whether distinct species inhabiting the same environments evolve similar body colors via shared sensory mechanisms. In this study, we tested whether two sympatric freshwater fish taxa, halfbeaks of the genus Nomorhamphus and ricefishes of the genus Oryzias in Sulawesi Island, converge in both body color and visual sensitivity. After reconstructing the phylogeny separately for Nomorhamphus and Oryzias using transcriptome‐wide sequences, we demonstrated positive correlations of body redness between these two taxa across environments, even after phylogenetic corrections, which support convergent evolution. However, substantial differences were observed in the expression profiles of opsin genes in the eyes between Nomorhamphus and Oryzias. Particularly, the expression levels of the long wavelength‐sensitive genes were negatively correlated between the taxa, indicating that they have different visual sensitivities despite living in similar light environments. Thus, the convergence of body colorations between these two freshwater fish taxa was not accompanied by convergence in opsin sensitivities. This system presents a case in which body color convergence can occur between sympatric species via different mechanisms.

Lake Poso, one of the ancient lakes of Sulawesi, Indonesia, has several endemic fish species, including the ricefishes (Oryzias nigrimas), local name rono pahit. Populations of Poso Lake endemic species are declining, due to the introduction of alien species, lakeshore development and watershed land-use changes. One way help maintain an O. nigrimas population is through captive breeding and domestication, for which knowledge of food habits is a pre-requisite. The purpose of this research was to study the food habits of O. nigrimas. The research was conducted during April 2018. Samples were collected from three sampling sites: Watudilana in Pamona Urban Village, Tolambo Village and Taipa Village. The Index of Preponderance (IP) and Relative Length of Gut (RLG) were calculated the results show that O. Nigrimas is an omnivorous-herbivorous fish with an average IP range of 57.73 to 70.75 for vegetable matter and 29.25-42.27 for animal food (prey), while the RGL range 2.48 to 3.26. Rhizosolenia sp. (IP 77.84) was the most dominant plant-based diet component, while unidentified Annelida larvae (IP 24.49) were the most common animal food.

The combination of high-throughput sequencing technology and environmental DNA (eDNA) analysis has the potential to be a powerful tool for comprehensive, non-invasive monitoring of species in the environment. To understand the correlation between the abundance of eDNA and that of species in natural environments, we have to obtain quantitative eDNA data, usually via individual assays for each species. The recently developed quantitative sequencing (qSeq) technique enables simultaneous phylogenetic identification and quantification of individual species by counting random tags added to the 5′ end of the target sequence during the first DNA synthesis. Here, we applied qSeq to eDNA analysis to test its effectiveness in biodiversity monitoring. eDNA was extracted from water samples taken over 4 days from aquaria containing five fish species (Hemigrammocypris neglectus, Candidia temminckii, Oryzias latipes, Rhinogobius flumineus, and Misgurnus anguillicaudatus), and quantified by qSeq and microfluidic digital PCR (dPCR) using a TaqMan probe. The eDNA abundance quantified by qSeq was consistent with that quantified by dPCR for each fish species at each sampling time. The correlation coefficients between qSeq and dPCR were 0.643, 0.859, and 0.786 for H. neglectus, O. latipes, and M. anguillicaudatus, respectively, indicating that qSeq accurately quantifies fish eDNA. [ABSTRACT FROM AUTHOR]

Heteroplasmy, the presence of multiple mitochondrial DNA (mtDNA) haplotypes within cells of an individual, is caused by mutation or paternal leakage. However, heteroplasmy is usually resolved to homoplasmy within a few generations because of germ-line bottlenecks; therefore, instances of heteroplasmy are limited in nature. Here, we report heteroplasmy in the ricefish species Oryzias matanensis , endemic to Lake Matano, an ancient lake in Sulawesi Island, in which one individual was known to have many heterozygous sites in the mitochondrial NADH dehydrogenase subunit 2 (ND2) gene. In this study, we cloned the ND2 gene for some additional individuals with heterozygous sites and demonstrated that they are truly heteroplasmic. Phylogenetic analysis revealed that the extra haplotype within the heteroplasmic O. matanensis individuals clustered with haplotypes of O. marmoratus , a congeneric species inhabiting adjacent lakes. This indicated that the heteroplasmy originated from paternal leakage due to interspecific hybridization. The extra haplotype was unique and contained two non-synonymous substitutions. These findings demonstrate that this hybridization-driven heteroplasmy was maintained across generations for a long time to the extent that the extra mitochondria evolved within the new host.

The inheritable impact of exposure to graphene oxide nanoparticles (GO NPs) on vertebrate germline during critical windows of gamete development remain undetermined to date. Here, we analyzed the transgenerational effects of exposure to nano-graphene oxide particles (nGO) synthesized in house with lateral dimensions 300-600 nm and surface charge of -36.8 mV on different developmental stages of germ cells (GCs): (1) during GCs undergoing early development and differentiation, and (2) during GCs undergoing gametogenesis and maturation in adulthood. Biocompatibility analyses in Japanese medaka embryos showed lethality above 1 µg/ml and also an aberrant increase in germ cell count of both males and females at doses below the lethal dose. However, no lethality or anomalies were evident in adults up to 45 µg/ml. Long term exposure of embryos and adults for 21 days resulted in reduced fecundity. This effect was transmitted to subsequent generations, F1 and F2. Importantly, the inheritable effects of nGO in adults were pronounced at a high dose of 10 µg/ml, while 1 µg/ml showed no impact on the germline indicating lower doses used in this study to be safe. Further, expressions of selected genes that adversely affected oocyte maturation were enhanced in F1 and F2 individuals. Interestingly, the inheritance patterns differed corresponding to the stage at which the fish received the exposure.

The simultaneous presence of micro(nano)plastics (MNPs) and pollutants represents a prevalent environmental challenge that necessitates understanding their combined impact on toxicity. This study examined the distribution of 5 μm (PS-MP5) and 50 nm (PS-NP50) polystyrene plastic particles during the early developmental stages of marine medaka (Oryzias melastigma) and assessed their combined toxicity with triphenyltin (TPT). Results showed that 2 mg/L PS-MP5 and PS-NP50 could adhere to the embryo surface. PS-NP50 can passively enter the larvae and accumulate predominantly in the intestine and head, while PS-MP5 cannot. Nonetheless, both types can be actively ingested by the larvae and distributed in the intestine. 2 mg/L PS-MNPs enhance the acute toxicity of TPT. Interestingly, high concentrations of PS-NP50 (20 mg/L) diminish the acute toxicity of TPT due to their sedimentation properties and interactions with TPT. 200 μg/L PS-MNPs and 200 ng/L TPT affect complement and coagulation cascade pathways and cardiac development of medaka larvae. PS-MNPs exacerbate TPT-induced cardiotoxicity, with PS-NP50 exhibiting stronger effects than PS-MP5, which may be related to the higher adsorption capacity of NPs to TPT and their ability to enter the embryos before hatching. This study elucidates the distribution of MNPs during the early developmental stages of marine medaka and their effects on TPT toxicity, offering a theoretical foundation for the ecological risk assessment of MNPs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Diazepam (DZP) residue has been frequently detected in wastewater, surface water, and groundwater due to its extensive use over the decades. In this study, we exposed female Japanese medaka (Oryzias latipes) to environmentally relevant doses of DZP (800 and 8000 ng/L) for 4 weeks, aimed to investigate their behavioral responses and possible links with ocular and brain oxidative stress homeostasis. As a result, DZP exposure could significantly reduce swimming activity (800 ng/L) and anxiety (800 and 8000 ng/L), indicating a sedative effect on medaka. The DZP exposure also significantly increased the social interaction in medaka at 8000 ng/L. Furthermore, exposure to DZP could alter the ocular and brain oxidative stress homeostasis in medaka. The ocular CAT activities significantly increased in the 800 ng/L-DZP groups, and the brain SOD, CAT, GST and MDA levels also significantly increased in both DZP exposure groups. Correlation analysis revealed that the ocular and brain oxidative stress induced by DZP exposure might play an important role in their behavioral toxicity to medaka. Our findings highlight the necessity to clarify the exact link between DZP exposure-induced oxidative stress in the neural and sensor systems and its behavioral toxicity to better assess the risks on nontarget aquatic species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Inc.)

In this paper, we present a voxel-based phantom of Medaka fish that can be used to assess the internal radiation doses that would be absorbed by different organs of this fish species if exposed to radioactive wastewater released into the ocean. The geometric model for fish was generated based on available Wavefront Object files for smooth-bodied Medaka fish organs, whereas due to the lack of Medaka fish material specification, the material model was constructed using material data appropriate to ICRP 110 adult male voxel-based phantom. Absorbed Fractions (AFs) and Specific Absorbed Fractions (SAFs) were calculated for eight organs of major interest as sources and for each organ as target at a set of discrete photon, electron, alpha and neutron energies. To validate the present model the calculated AFs in the studied organs were compared to ones obtained in similar organs in a voxel-based phantom of another teleost fish species called Limanda limanda. The results presented are consistent with the reference dosimetric data. We concluded that the Medaka model can be used in radioecology research to improve marine radiation protection., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest to declare., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Nanoplastics can interact with antibiotics, altering their bioavailability and the ensuing toxicity in marine organisms. It is reported that plain polystyrene (PS) nanoplastics decrease the bioavailability and adverse effects of sulfamethazine (SMZ) on the gut microbiota in Oryzias melastigma. However, the influence of surface functional groups on the combined effects with SMZ remains largely unknown. In this study, adult O. melastigma were fed diet amended with 4.62 mg/g SMZ and 3.65 mg/g nanoplastics (i.e., plain PS, PS-COOH and PS-NH 2 ) for 30 days (F0-E), followed by a depuration period of 21 days (F0-D). In addition, the eggs produced on the last day of exposure were cultured under standard protocols without further exposure for 2 months (F1 fish). The results showed that the alpha diversity or the bacterial community of gut microbiota did not differ among the SMZ + PS, SMZ + PS-COOH, and SMZ + PS-NH 2 groups in the F0-E and F1 fish. Interestingly, during the depuration, a clear recovery of gut microbiota (e.g., increases in the alpha diversity, beneficial bacteria abundances and network complexity) was found in the SMZ + PS group, but not for the SMZ + PS-COOH and SMZ + PS-NH 2 groups, indicating that PS-COOH and PS-NH 2 could prolong the toxic effect of SMZ and hinder the recovery of gut microbiota. Compared to plain PS, lower egestion rates of PS-COOH and PS-NH 2 were observed in O. melastigma. In addition, under the simulated fish digest conditions, the SMZ-loaded PS-NH 2 was found to desorb more SMZ than the loaded PS and PS-COOH. These results suggested that the surface -COOH and -NH 2 groups on PS could influence their egestion efficiency and the adsorption/desorption behavior with SMZ, resulting in a long-lasting SMZ stress in the gut during the depuration phase. Our findings highlight the complexity of the carrier effect and ecological risk of surface-charged nanoplastics and the interactions between nanoplastics and antibiotics in natural environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Medaka Oryzias latipes is a small freshwater fish widely distributed in Japan. It is a popular ornamental fish and now has been recognized as an important model organism in many areas of biological research. Here we report microsporidian infections for the first time in medaka, from 2 research facilities and a wild population. Infected medaka exhibited abnormal appearance with whitish trunk muscle, and microsporidian spores were detected from the affected tissue. The size of spores was similar in all the three cases: 7.0 μm in length and 3.7-4.2 μm in width. In the histological observation, numerous sporophorous vesicles containing spores or other developmental stages were observed within the myocytes of the trunk muscle. Nucleotide sequence of the ribosomal RNA gene was determined and it was identical among all three cases. A BLAST search revealed it shared 99.5-99.6% identity with Pleistophora hyphessobryconis, a microsporidian known to infect >20 freshwater fish species. Light microscopic observation of spores and histological features also indicated the microsporidian infection in medaka is caused by P. hyphessobryconis. This is the first record of the microsporidian species from medaka and from Japan., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to declare., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Maternal nutritional status can affect development and metabolic phenotypes of progeny in animals. The effects of maternal diet are thought to be mediated mainly by changes inside oocytes such as organelles, maternal RNAs, and metabolites. However, to what extent each factor contributes to offspring phenotypes remains uncertain, especially in viviparous mammalian systems, where factors other than oocytes, such as placenta and milk, need to be considered. Here, using the medaka fish as an oviparous vertebrate model, we examined whether maternal high-fat diet (mHFD) feeding affects offspring development and what kind of changes occur in the contents of mature eggs. We found that mHFD caused the high frequency of embryonic deformities of offspring, accompanied by downregulation of transcription- and translation-related genes and zygotic transcripts at the blastula stage. Transcriptomic and metabolomic analyses of mature eggs suggested decreased catabolism of amino acids and glycogen, moderate upregulation of endoplasmic reticulum stress-related genes, and elevated lipid levels in mHFD eggs. Furthermore, high-fat diet females showed a higher incidence of oocyte atresia and downregulation of egg protein genes in the liver. These data suggest that attenuated amino acid catabolism triggered by decreased yolk protein load/processing, as well as elevated lipid levels inside eggs, are the prime candidates that account for the higher incidence of embryonic deformities in mHFD offspring. Our study presents a comprehensive data on the changes inside eggs in a mHFD model of nonmammalian vertebrates and provides insights into the mechanisms of parental nutritional effects on offspring., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Toxicity observed in aquatic ecosystems often cannot be explained by the action of a single pollutant. Likewise, evaluation standards formulated by a single effect cannot truly reflect the environmental quality requirements. The study of mixtures is needed to provide environmental relevance and knowledge of combined toxicity. In this study, the embryos of Japanese medaka (Oryzias latipes) were treated with individual and binary mixture of copper (Cu) and cadmium (Cd) until 12 days post-fertilization (dpf). Hatching, mortality, development, histology and gene expression were assessed. Our results showed that the highest concentration mixture of Cd (10 mg/L) and Cu (1 mg/L) affected survival, hatching time and hatching success. Occurrence of uninflated swim bladder was the highest (value) with exposure to 10 mg/L Cd. Swim bladder was commonly over-inflated in a mixture (0.1 mg/L Cd + 1.0 mg/L Cu) exposure. Individuals exposed to the mixture (0.1 Cd + 1.0 Cu mg/L) showed up to a 7.69% increase in swim bladder area compared to the control group. The mixtures containing 0.1 or 10 mg/L Cd, each with 1.0 mg/L Cu resulted in significantly increased of Pbx1b expression, higher than any Cd or Cu alone (p < 0.01). In the co-exposure group (0.1/10 Cd + 1.0 Cu mg/L), Pbx1b expression was found at 12 dpf but not 7 dpf in controls. Higher concentrations of Cd may progressively reduce Pbx1b expression, potentially explaining why 75% of individuals in the 10 mg/L Cd group failed to inflate their swim bladders. Additionally, the swim bladder proved to be a valuable bio-indicator for biological evaluation., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

The COVID-19 pandemic has resulted in huge amounts of face masks worldwide. However, there is a lack of awareness on the additives and their potential risk to aquatic ecosystems of face masks. To address this issue, the additives and their toxicity in 13 face masks (e.g., polypropylene, polyethylene, and polylactic acid) were determined using nontarget analysis and bioassays. A total of 826 organic additives including intermediates (14.8%), surfactants (9.3%), plasticizers (8.2%), and antioxidants (6.1%) were tentatively identified, with 213 compounds being assigned confidence levels of 1 and 2. Interestingly, polylactic acid masks contained more additives than most polypropylene or polyethylene masks. Among these additives, the concentration of tris(2-ethylhexyl) phosphate in masks was 9.4-978.2 ng/g with a 100% detection frequency. Furthermore, 13 metals such as zinc (up to 202.0 μg/g), copper (32.5 μg/g), and chromium (up to 5.7 μg/g) were detected in the face masks. The methanol extracts of the masks showed the developmental toxicity, swimming behavior, and/or endocrine disruption in embryos/larvae of Oryzias melastigma . The findings demonstrate that face masks contain various toxic additives to marine medaka, which deserves close attention to pollution by face masks.

Small teleost fishes such as zebrafish and medaka show remarkable regeneration capabilities upon tissue injury or amputation. To elucidate cellular mechanisms of teleost tissue repair and regeneration processes, the Cre/LoxP recombination system for cell lineage tracing is a widely used technique. In this chapter, we describe protocols used for inducible Cre/LoxP recombination-mediated lineage tracing of osteoblast progenitors during medaka fin regeneration as well as during the repair of osteoporosis-like bone lesions in the medaka vertebral column. Our approach can be adapted for lineage tracing of other cell populations in the regenerating teleost fin or in other tissues undergoing repair., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Purpose: Zebrafish, a small fish model, exhibits a multipotent ability for retinal regeneration after damage throughout its lifetime. Compared with zebrafish, birds and mammals exhibit such a regenerative capacity only during the embryonic period, and this capacity decreases with age. In medaka, another small fish model that has also been used extensively in biological research, the retina's inner nuclear layer (INL) failed to regenerate after injury in the hatchling at eight days postfertilization (dpf). We characterized the regenerative process of the embryonic retina when the retinal injury occurred during the early embryonic period in medaka., Methods: We employed a 10 Gy dose of gamma-ray irradiation to initiate retinal injury in medaka embryos at 3 dpf and performed histopathological analyses up to 21 dpf., Results: One day after irradiation, numerous apoptotic neurons were observed in the INL; however, these neurons were rarely observed in the ciliary marginal zone and the photoreceptor layer. Numerous pyknotic cells were clustered in the irradiated retina until two days after irradiation. These disappeared four days after irradiation, but the abnormal bridging structures between the INL and ganglion cell layer (GCL) were present until 11 days after irradiation, and the neural layers were completely regenerated 18 days after irradiation. After gamma-ray irradiation, the spindle-like Müller glial cells in the INL became rounder but did not lose their ability to express SOX2., Conclusions: Irradiated retina at 3 dpf of medaka embryos could be completely regenerated at 18 days after irradiation (21 dpf), although the abnormal layer structures bridging the INL and GCL were transiently formed in the retinas of all the irradiated embryos. Four days after irradiation, embryonic medaka Müller glia were reduced in number but maintained SOX2 expression as in nonirradiated embryos. This finding contrasts with previous reports that 8 dpf medaka larvae could not fully regenerate damaged retinas because of loss of SOX2 expression.

Kisspeptin (product of the kiss1 gene) is the most potent known activator of the hypothalamo-pituitary-gonadal axis. Both kiss1 and the kisspeptin receptor are highly expressed in the hypothalamus of vertebrates, and low doses of kisspeptin have a robust and long-lasting stimulatory effect on the rate of action potential firing of hypophysiotropic gonadotropin releasing hormone-1 (GnRH1) neurons in mice. Fish have multiple populations of GnRH neurons distinguished by their location in the brain and the GnRH gene that they express. GnRH3 neurons located in the terminal nerve (TN) associated with the olfactory bulb are neuromodulatory and do not play a direct role in regulating pituitary-gonadal function. In medaka fish, the electrical activity of TN-GnRH3 neurons is modulated by visual cues from conspecifics, and is thought to act as a transmitter of information from the external environment to the central nervous system. TN-GnRH3 neurons also play a role in sexual motivation and arousal states, making them an important population of neurons to study for understanding coordination of complex behaviors. We investigated the role of kisspeptin in regulating electrical activity of TN-GnRH3 neurons in adult medaka. Using electrophysiology in an intact brain preparation, we show that a relatively brief treatment with 100 nM of kisspeptin had a long-lasting stimulatory effect on the electrical activity of an extrahypothalamic population of GnRH neurons. Dose-response analysis suggests a relatively narrow activational range of this neuropeptide. Further, blocking action potential firing with tetrodotoxin and blocking synaptic transmission with a low Ca(2+)/high Mg(2+) solution inhibited the stimulatory action of kisspeptin on electrical activity, indicating that kisspeptin is acting indirectly through synaptic regulation to excite TN-GnRH3 neurons. Our findings provide a new perspective on kisspeptin's broader functions within the central nervous system, through its regulation of an extrahypothalamic population of GnRH neurons involved in multiple neuromodulatory functions.