Breeding Zebrafish: A Review of Different Methods and a Discussion on Standardization

Water properties and quality of the largest rice production region in Japan and their influence on the reproduction of zebrafish

The health of freshwater aquarium fish and their breeding success depend critically on the quality of tap water. In general, tap water in Japan is potable, although the properties of tap water vary among regions in Japan. The city of Niigata is located in the largest rice production region of Japan. We have faced challenges concerning the reproduction of freshwater aquarium fish in Niigata. To determine whether water properties and quality affect the reproduction of aquarium fish in Niigata, we investigated the chemical properties of water and raised zebrafish in water from three different sources, namely tap water of Niigata in May, artificial freshwater (i.e., prepared via reverse osmosis), and natural spring water of Gosen, to document any effects on their sexual maturation and reproduction. We found that the tap water of Niigata was not stable throughout a year (median electrical conductivity = 147.1 μS/cm; SD = 25.6), with springtime lower than the first quartile. We also found that low concentrations of four pesticides in the tap water have been detected in May (max. concentration in 2020, bromobutide 2,000 ng/L, butachlor 600 ng/L, pyraclonil 200 ng/L, ipfencarbazone 20 ng/L). Moreover, rearing zebrafish in tap water negatively influenced both fish growth and reproduction: The sex ratio of adults was male biased (proportion of F0 male 70.8%); the average total length (30.5 mm) and weight (182 mg) of F0 males was decreased; the GSI of F0 females (9.7%) was decreased; the fecundity (the mating success 58.7%; the number of F1 eggs 63.1) of adults was reduced. Rearing in artificial freshwater could improve these outcomes (the sex ratio 55.7%; the total length of F0 males 31.8 mm; the weight of F0 males 211 mg; the GSI of F0 females 11.7%; the mating success 72.6%; the number of F1 eggs 99.0), whereas rearing in natural spring water from Gosen could improve the sex ratio (56.3%) and the weight of F0 males (200 mg), but not the others. Therefore, artificial freshwater made via reverse osmosis should be used for breeding freshwater aquarium fish in rice production region like Niigata. Finally, our results demonstrate that the reproduction of freshwater aquarium fish can serve as a bioindicator of low levels of organic pollutants in tap water and thus provide a basis for evaluating the safety of tap water for human consumption.

Ethylene thiourea exposure induces neurobehavioral toxicity in zebrafish by disrupting axon growth and neuromuscular junctions

Ethylene thiourea (ETU) converted from ethylene bisdithiocarbamate (EBDC) fungicides has aroused great concern because of its prevalence and harmful effects. Although ETU-induced neurotoxicity has been reported, the potential mechanisms remain unclear. This study provided insights into its neurotoxic effects at environmentally relevant concentrations in zebrafish. Our findings showed that embryonic exposure to ETU decreased the hatch rate and delayed somite development. Furthermore, ETU treatment significantly reduced the dark velocity in the locomotion assay. The upregulated tendency of the mitogen-activated protein kinases (MAPK) pathway (mknk1, atf4, mapkapk3) screened by transcriptome analysis implied motor neuron degeneration, which was validated by subsequent morphological observation, as axon length and branches were truncated in the 62.5 µg/L ETU group. However, although the rescue experiment with a p38 MAPK inhibitor (SB203580) successfully ameliorated axon degeneration, it failed to reverse the locomotion behaviors. Further exploration of transcriptome data revealed the varied expression of presynaptic scaffold protein-related genes (pcloa, pclob, bsna), whose downregulation might impair the neuromuscular junction (NMJ). Therefore, we reasonably suspected that ETU-induced neurobehavioral deficits might result from the combined effects of the MAPK pathway and presynaptic proteins. Considering this, we highlighted the necessity to take precautions and early interventions for susceptible ETU-exposed populations.

The association of cysteine to thiomersal attenuates its apoptosis-mediated cytotoxicity in zebrafish

Thiomersal (TM) is an excellent preservative that is used in a wide variety of products, like pharmaceuticals, cosmetics, and vaccines, etc. Its usage has been in decline because of safety concerns. Since vaccine production is on the rise, its use may increase further in low-income and developing countries, as a cost-effective vaccine preservative. Further, Thiomersal is still being used as an essential component in various pharmaceutical preparations. In this light, the present study addresses its mechanism of toxicity in zebrafish and unveils a novel strategy for lessening its negative effects by conjugating cysteine to it, while retaining its antibacterial efficacy. We show that the mitochondrial membrane potential is destabilised by TM, leading to the induction of apoptosis. Interestingly, TM-cysteine conjugate (at a ratio of 1:1) showed no toxicity in zebrafish, whereas TM alone was highly toxic. Importantly, assaying for the bactericidal activity, tested using Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA), revealed that the conjugate retains the antibacterial activity, demonstrating that the TM-cysteine conjugate is a safer alternative to TM as a vaccine preservative, and in all the other products that still use TM.

An Evaluation of Zebrafish, an Emerging Model Analyzing the Effects of Toxicants on Cognitive and Neuromuscular Function

An emerging alternative to conventional animal models in toxicology research is the zebrafish. Their accelerated development, regenerative capacity, transparent physical appearance, ability to be genetically manipulated, and ease of housing and care make them feasible and efficient experimental models. Nonetheless, their most esteemed asset is their 70% (+) genetic similarity with the human genome, which allows the model to be used in a variety of clinically relevant studies. With these attributes, we propose the zebrafish is an excellent model for analyzing cognitive and neuromuscular responses when exposed to toxicants. Neurocognition can be readily analyzed using visual discrimination, memory and learning, and social behavior testing. Neuromuscular function can be analyzed using techniques such as the startle response, assessment of activity level, and evaluation of critical swimming speed. Furthermore, selectively mutated zebrafish is another novel application of this species in behavioral and pharmacological studies, which can be exploited in toxicological studies. There is a critical need in biomedical research to discover ethical and cost-effective methods to develop new products, including drugs. Through mutagenesis, zebrafish models have become key in meeting this need by advancing the field in numerous areas of biomedical research.

Dynamic Regulation of brsk2 in the Social and Motor Development of Zebrafish: A Developmental Behavior Analysis

Both social and motor development play an essential role in an individual's physical, psychological, and social well-being. It is essential to conduct a dynamic analysis at multiple time points during the developmental process as it helps us better understand and evaluate the trajectory and changes in individual development. Recently, some studies found that mutations in the BRSK2 gene may contribute to motor impairments, delays in achieving motor milestones, and deficits in social behavior and communication skills in patients. However, little is known about the dynamic analysis of social and motor development at multiple time points during the development of the brsk2 gene. We generated a novel brsk2-deficient (brsk2ab-/-) zebrafish model through CRISPR/Cas9 editing and conducted comprehensive morphological and neurobehavioral evaluations, including that of locomotor behaviors, social behaviors, and anxiety behaviors from the larval to adult stages of development. Compared to wild-type zebrafish, brsk2ab-/- zebrafish exhibited a catch-up growth pattern of body length and gradually improved locomotor activities during the developmental process. In contrast, multimodal behavior tests showed that the brsk2ab-/- zebrafish displayed escalating social deficiency and anxiety-like behaviors over time. We reported for the first time that the brsk2 gene had dynamic regulatory effects on motor and social development. It helps us understand developmental trends, capture changes, facilitate early interventions, and provide personalized support and development opportunities for individuals.

Identification of zebrafish GIGYF2 presents in egg/embryo as an antibacterial protein

Previous studies have shown that GIGYF2 plays multiple roles, but its overall biological function remains poor-defined. Here we clearly demonstrated that zebrafish (Danio rerio) GIGYF2 has GYF domain and gigyf2 mainly expressed in caudal fin, brain, eyes and testis in a tissue specific manner, and was most abundant in brain and testis. GYF domain of GIGYF2 was a peptidoglycan (PGN), lipopolysaccharide (LPS)- and lipoteichoic acid (LTA)- binding protein abundantly stored in the testis/embryos of zebrafish, acting not only as a pattern recognition receptor, but also as an effector molecule, capable of inhibiting the growth of gram-positive and -negative bacteria. Furthermore, we reveal that the residues of GIGYF2 positioned at 582-601 and 848-865 were indispensable for GIGYF2 antibacterial activity. Additionally, site-directed mutation could improve antibacterial activities. Collectively, our results indicate that zebrafish GYF domain of GIGYF2 recognize bacterial characteristic molecules PGN, LPS and LTA, and directly kill bacteria as an antibacterial effector. This work also provides another angle for understanding the biological roles of GIGYF2.

Exogenous 2-keto-L-gulonic Acid Supplementation as a Novel Approach to Enhancing L-ascorbic Acid Biosynthesis in Zebrafish (Danio rerio)

L-ascorbic acid (ASA) is a micronutrient that is essential for reproduction, growth, and immunity in animals. Due to the loss of enzyme L-gulono-1,4-lactone oxidase (GLO), most aquatic animals lack the capacity for ASA biosynthesis and therefore require supplementation with exogenous ASA. Recent studies have shown that 2-keto-L-gulonic acid (2KGA), a novel potential precursor of ASA, can enhance plant growth and improve stress resistance by promoting the synthesis and accumulation of ASA. Our hypothesis is that 2-keto-L-gulonic acid (2KGA) plays a similar role in aquatic animals. To investigate this, we conducted an in vivo trial to examine the effects of exogenous 2KGA supplementation on ASA metabolism and growth of zebrafish (Danio rerio). Zebrafish were categorized into groups based on their dietary intake, including a basal diet (CK group), a basal diet supplemented with 800 mg/kg ASA (ASA group), and 800 mg/kg 2KGA-Na (2KGA group) for a duration of three weeks. The results demonstrated a significant increase in ASA content in zebrafish treated with 2KGA (34.82% increase, p < 0.05) compared to the CK group, reaching a consistent level with the ASA group (39.61% increase, p < 0.05). Furthermore, the supplementation of 2KGA significantly improved growth parameters relevant to zebrafish (specific growth rate increased by 129.04%, p < 0.05) and enhanced feed utilization (feed intake increased by 15.65%, p < 0.05). Positive correlations were observed between growth parameters, feed utilization, whole-body chemical composition, and ASA content. Our findings suggest that supplementation with exogenous 2KGA can serve as a novel approach for elevating ASA synthesis in aquatic animals, and further investigation of its underlying mechanism is required.

Quantitative characterization of zebrafish development based on multiple classifications using Mueller matrix OCT

Organ development analysis plays an important role in assessing an individual' s growth health. In this study, we present a non-invasive method for the quantitative characterization of zebrafish multiple organs during their growth, utilizing Mueller matrix optical coherence tomography (Mueller matrix OCT) in combination with deep learning. Firstly, Mueller matrix OCT was employed to acquire 3D images of zebrafish during development. Subsequently, a deep learning based U-Net network was applied to segment various anatomical structures, including the body, eyes, spine, yolk sac, and swim bladder of the zebrafish. Following segmentation, the volume of each organ was calculated. Finally, the development and proportional trends of zebrafish embryos and organs from day 1 to day 19 were quantitatively analyzed. The obtained quantitative results revealed that the volume development of the fish body and individual organs exhibited a steady growth trend. Additionally, smaller organs, such as the spine and swim bladder, were successfully quantified during the growth process. Our findings demonstrate that the combination of Mueller matrix OCT and deep learning effectively quantify the development of various organs throughout zebrafish embryonic development. This approach offers a more intuitive and efficient monitoring method for clinical medicine and developmental biology studies.

Substrate colour guides turquoise killifish's (Nothobranchius furzeri) choice of preferred spawning habitat

Turquoise killifish (Nothobranchius furzeri) is a promising new model species used in biomedical and ecological laboratory experiments, and should be kept under optimal conditions to ensure fish welfare and the quality of science. While the popularity of this model species is rapidly increasing, we need to improve our understanding of how the species interacts with its environment to optimize its husbandry. Specifically, turquoise killifish are substrate spawners that bury their eggs in the sediment, which can be accommodated under captive conditions, but it is not yet known whether or not turquoise killifish have a preference for a specific sediment colour. Here, we performed a laboratory experiment in which fish could choose between white, orange and black sand for spawning, colours which are relevant in both laboratory and field conditions. We assessed their preference in the context of single breeding pairs, as well as in a social group setting. Additionally, we also assessed the preference of individuals for a white versus black background in a nonmating context. Single breeding pairs deposited over 3.5 times more eggs in black compared to orange or white sand. Similarly, fish in social groups deposited over 3.5 times more eggs in black compared to orange sand, which in turn was over two times higher than that in white sand. Fish showed a slight preference for the black compared to the white zone in a nonmating context, but this did not correlate with substrate choice during the spawning tests. The results suggest that turquoise killifish select their preferred spawning location based on the colour of the substrate. These findings contribute to our understanding of the species' biology and can help to guide good welfare and scientific practice.

Toxic effects and bioaccumulation of pinacolyl methylphosphonate acid in zebrafish following soman exposure to a water environment

Soman has been shown to be highly neurotoxic and can be easily degraded to produce pinacolyl methylphosphonate acid (PMPA). Thus, the perniciousness of PMPA deserved serious attention after soman was exposed to the environment. However, the toxicity of PMPA was not clearly elucidated to date. In this regard, the objective of this study was to determine if PMPA could pose an environmental risk after soman exposure to a water environment. In this study, the toxicity and bioaccumulation assessments of PMPA were carried out on zebrafish. Histological examination was used to assess the toxicity of PMPA in zebrafish and revealed that PMPA has chronic toxicity in view of tissue injury. The contents of PMPA in whole zebrafish and tissues were determined after soman exposure. The result showed that PMPA bioaccumulated in the whole zebrafish and tissue, especially the liver and intestinal tissues. This is the first report showing that the hydrolyzate of a G-series chemical nerve agent could accumulate in organisms. This study offers novel insights into the environmental risk assessments associated with soman exposure to a water environment.

Effect of Early Peptide Diets on Zebrafish Skeletal Development

Incorporation of dietary peptides has been correlated with decreased presence of skeletal abnormalities in marine larvae. In an attempt to clarify the effect of smaller protein fractions on fish larval and post-larval skeleton, we designed three isoenergetic diets with partial substitution of their protein content with 0% (C), 6% (P6) and 12% (P12) shrimp di- and tripeptides. Experimental diets were tested in zebrafish under two regimes, with inclusion (ADF-Artemia and dry feed) or lack (DF-dry feed only) of live food. Results at the end of metamorphosis highlight the beneficial effect of P12 on growth, survival and early skeletal quality when dry diets are provided from first feeding (DF). Exclusive feeding with P12 also increased the musculoskeletal resistance of the post-larval skeleton against the swimming challenge test (SCT). On the contrary, Artemia inclusion (ADF) overruled any peptide effect in total fish performance. Given the unknown species' larval nutrient requirements, a 12% dietary peptide incorporation is proposed for successful rearing without live food. A potential nutritional control of the larval and post-larval skeletal development even in aquaculture species is suggested. Limitations of the current molecular analysis are discussed to enable the future identification of the peptide-driven regulatory pathways.

Structural characterization and anti-inflammatory effects of an arabinan isolated from Rehmannia glutinosa Libosch

Considering that natural polysaccharides are potential anti-inflammatory agents, in this study, an arabinan (RGP70-2) was isolated and purified from Rehmannia glutinosa Libosch. (R. glutinosa) and its structure was characterized. RGP70-2 was a homogeneous polysaccharide with a molecular weight of 6.7 kDa, with the main backbone comprising →5)-α-L-Araf-(1→, →3)-α-L-Araf-(1→, →2,3,5)-α-L-Araf-(1→, and →2,5)-α-L-Araf-(1 → linkages and the side chain comprising an α-L-Araf-(1 → linkage. In vivo experiments showed that RGP70-2 inhibited ROS production and downregulated the expression of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). In vitro experiments showed that RGP70-2 decreased levels of pro-inflammatory cytokines, inhibited ROS production, and attenuated NF-κB-p65 translocation from the cytoplasm to the nucleus. Our results showed that RGP70-2 may delay inflammation by regulating the ROS-NF-κB pathway. Thus, RGP70-2 has potential applications as an anti-inflammatory agent in the biopharmaceutical industry.

Comparative Study on the Structural Properties and Bioactivities of Three Different Molecular Weights of Lycium barbarum Polysaccharides

The molecular weight, the triple-helix conformation, the monosaccharide content, the manner of glycosidic linkages, and the polysaccharide conjugates of polysaccharides all affect bioactivity. The purpose of this study was to determine how different molecular weights affected the bioactivity of the Lycium barbarum polysaccharides (LBPs). By ethanol-graded precipitation and ultrafiltration membrane separation, one oligosaccharide (LBPs-1, 1.912 kDa) and two polysaccharides (LBPs-2, 7.481 kDa; LBPs-3, 46.239 kDa) were obtained from Lycium barbarum. While the major component of LBPs-1 and LBPs-2 was glucose, the main constituents of LBPs-3 were arabinose, galactose, and glucose. LBPs-2 and LBPs-3 exhibited triple-helix conformations, as evidenced by the Congo red experiment and AFM data. Sugar residues of LBPs-2 and LBPs-3 were elucidated by NMR spectra. The polysaccharides (LBPs-2 and LBPs-3) exhibited much higher antioxidant capacities than oligosaccharide (LBPs-1). LBPs-3 showed higher oxygen radical absorbance capacity (ORAC) and superoxide dismutase (SOD) activity than LBPs-2, but a lower capability for scavenging ABTS⁺ radicals. In zebrafish, LBPs-2 and LBPs-3 boosted the growth of T-lymphocytes and macrophages, enhanced the immunological response, and mitigated the immune damage generated by VTI. In addition to the molecular weight, the results indicated that the biological activities would be the consequence of various aspects, such as the monosaccharide composition ratio, the chemical composition, and the chemical reaction mechanism.

Zebrafish (Danio rerio): A newcomer with great promise in behavioral neuroscience

Behavioral neuroscience is an interdisciplinary field aimed at understanding the neurobiology of behavior. Numerous investigators turn to animals to model and understand the mechanisms underlying vertebrate brain function including human brain disorders, species that share evolutionary history with us. The zebrafish is a relatively new study species for such purposes. However, as this review attempts to demonstrate, it will likely have a good future in behavioral neuroscience. It is a simple vertebrate that is small and cheap to keep and study in the laboratory. Yet, it is similar enough to our own species, thus, we are able to use it for both translational as well as basic research. In this invited review, I will discuss its advantages and some of its disadvantages, the reasons and counterarguments why it should or should not be employed in research. I will focus on its utility in behavioral neuroscience, and will also provide a brief historical account of the evolution between zebrafish research and the science represented by the International Behavioral Neuroscience Society.

Zebrafish - The Neurobehavioural Model in Trend

Zebrafish (Danio rerio) is currently in vogue as a prevalently used experimental model for studies concerning neurobehavioural disorders and associated fields. Since the 1960s, this model has succeeded in breaking most barriers faced in the hunt for an experimental model. From its appearance to its high parity with human beings genetically, this model renders itself as an advantageous experimental lab animal. Neurobehavioural disorders have always posed an arduous task in terms of their detection as well as in determining their exact etiology. They are still, in most cases, diseases of interest for inventing or discovering novel pharmacological interventions. Thus, the need for a harbinger experimental model for studying neurobehaviours is escalating. Ensuring the same model is used for studying several neuro-studies conserves the results from inter-species variations. For this, we need a model that satisfies all the pre-requisite conditions to be made the final choice of model for neurobehavioural studies. This review recapitulates the progress of zebrafish as an experimental model with its most up-to-the-minute advances in the area. Various tests, assays, and responses employed using zebrafish in screening neuroactive drugs have been tabulated effectively. The tools, techniques, protocols, and apparatuses that bolster zebrafish studies are discussed. The probable research that can be done using zebrafish has also been briefly outlined. The various breeding and maintenance methods employed, along with the information on various strains available and most commonly used, are also elaborated upon, supplementing Zebrafish's use in neuroscience.

The role of transformation in the risks of chemically exfoliated molybdenum disulfide nanosheets to the aquatic environment

While the effects of environmental factors (e.g., coexisting organic macromolecules and solar irradiation) on the phase transformation and oxidative dissolution of chemically exfoliated molybdenum nanosheets (ceMoS₂) have been recognized, the effects of environmental processes on the subsequent biological impacts of ceMoS₂ are still poorly understood. In this study, the bioavailability and transitions in chemical speciation occurring during the aging process are demonstrated to be key factors causing ceMoS₂ to affect aquatic organisms. The lower survival rate of embryonic zebrafish with aged (i.e., sunlight-irradiated and dark-ambient-aged) ceMoS₂, compared to that with freshly prepared ceMoS₂, was due to the release of ionic aging products (mainly acidic Mo species) throughout the oxidative dissolution of ceMoS₂. The released soluble molybdenum interacted with natural organic matter (NOM) depending on their functionality, and this attenuated the toxicity caused by ceMoS₂ to different degrees. Toxicity triggered by aged ceMoS₂ under both dark and irradiated conditions was significantly reduced by Suwannee River NOM due to the formation of complexes with ionic Mo species, which was established by Mo K-edge X-ray absorption spectroscopy. The findings provide useful insights for comprehending the impacts of ceMoS₂ on aquatic organisms and guidance for the prevention measures necessary in the applications of MoS₂ nanosheets.

Researchers, animal support and regulatory staff: symbiosis or antagonism?

Animals are studied en masse by biologists around the world in a variety of biomedical and basic research studies. All this research benefits humankind and animals alike as it tackles a wide variety of problems ranging from those of conservation biology to medicine. Research with animal subjects is a complex endeavor that requires the cooperation and collaboration of a large number of experts, from the principal investigator through technicians and vivarium staff to regulatory experts. The research must be conducted in a humane manner that adheres to acceptable practices regulated by local, state and federal guidelines, rules and the law. In this short opinion article, we examine the current state of affairs regarding how researchers, animal support staff and regulatory experts work together. We pay particular attention to potential conflicts that may arise from the occasionally distinct roles played by those involved in animal research, and we provide some suggestions as short- and long-term remedies that have not been previously discussed in the literature.

Hydrogen sulfide-induced oxidative stress mediated apoptosis via mitochondria pathway in embryo-larval stages of zebrafish

Hydrogen sulfide (H₂S), a highly toxic gas, has become a polluting gas that cannot be ignored, while H₂S exposure results in acute or chronic poisoning or even death in humans or animals and plants, but the relevant mechanisms remain poorly understood. In this study, 9-day-old zebrafish larvae were exposed continuously to culture medium containing 30 μM survival rate was counted on H₂S, and our results indicated that H₂S exposure increased intracellular ROS, Ca²⁺, NO and MDA contents and decreased SOD activity, meaning that H₂S caused oxidative stress in embryo-larval stages of zebrafish. Furthermore, we found that transgenic zebrafish (cms Tg/+ AB) displayed a lower fluorescence intensity, and cytochrome c oxidase (COX) activity and JC-1 monomer fluorescence ratio increased under H₂S treatment conditions. These findings indicated that H₂S caused mitochondrial dysfunction. Moreover, in this experiment, after H₂S treatment, the increase of apoptotic cells, activity of caspase 3 and transcription of typical apoptosis-associated genes including BCL2 associated agonist of cell death (Bad), and BCL2 associated X apoptosis (Baxa) and so on were found, which suggested that H₂S caused apoptosis in zebrafish larvae. Therefore, our data meant that H₂S-traggered oxidative stress mediate mitochondrial dysfunction, thus triggering apoptosis. In conclusion, oxidative stress triggered H₂S-induced apoptosis via mitochondria pathway in embryo-larval stages of zebrafish.

Improving zebrafish laboratory welfare and scientific research through understanding their natural history

Globally, millions of zebrafish (Danio rerio) are used for scientific laboratory experiments for which researchers have a duty of care, with legal obligations to consider their welfare. Considering the growing use of the zebrafish as a vertebrate model for addressing a diverse range of scientific questions, optimising their laboratory conditions is of major importance for both welfare and improving scientific research. However, most guidelines for the care and breeding of zebrafish for research are concerned primarily with maximising production and minimising costs and pay little attention to the effects on welfare of the environments in which the fish are maintained, or how those conditions affect their scientific research. Here we review the physical and social conditions in which laboratory zebrafish are kept, identifying and drawing attention to factors likely to affect their welfare and experimental science. We also identify a fundamental lack knowledge of how zebrafish interact with many biotic and abiotic features in their natural environment to support ways to optimise zebrafish health and well-being in the laboratory, and in turn the quality of scientific data produced. We advocate that the conditions under which zebrafish are maintained need to become a more integral part of research and that we understand more fully how they influence experimental outcome and in turn interpretations of the data generated.

Toxicity of spike fragments SARS-CoV-2 S protein for zebrafish: A tool to study its hazardous for human health?

Despite the significant increase in the generation of SARS-CoV-2 contaminated domestic and hospital wastewater, little is known about the ecotoxicological effects of the virus or its structural components in freshwater vertebrates. In this context, this study evaluated the deleterious effects caused by SARS-CoV-2 Spike protein on the health of Danio rerio, zebrafish. We demonstrated, for the first time, that zebrafish injected with fragment 16 to 165 (rSpike), which corresponds to the N-terminal portion of the protein, presented mortalities and adverse effects on liver, kidney, ovary and brain tissues. The conserved genetic homology between zebrafish and humans might be one of the reasons for the intense toxic effects followed inflammatory reaction from the immune system of zebrafish to rSpike which provoked damage to organs in a similar pattern as happen in severe cases of COVID-19 in humans, and, resulted in 78,6% of survival rate in female adults during the first seven days. The application of spike protein in zebrafish was highly toxic that is suitable for future studies to gather valuable information about ecotoxicological impacts, as well as vaccine responses and therapeutic approaches in human medicine. Therefore, besides representing an important tool to assess the harmful effects of SARS-CoV-2 in the aquatic environment, we present the zebrafish as an animal model for translational COVID-19 research.

Characterization and immunomodulatory effect of an alkali-extracted galactomannan from Morchella esculenta

In our continuous exploration for bioactive polysaccharides, a novel polysaccharide FMP-2 was isolated and purified from the fruiting bodies of Morchella esculenta by alkali-assisted extraction. FMP-2 had an average molecular weight of 1.09 × 10⁶ Da and contained mannose, glucuronic acid, glucose, galactose, and arabinose in a molar ratio of 4.10:0.22:1.00:5.75:0.44. The backbone of FMP-2 mainly consisted of 1,2-α-D-Galp, 1,6-α-D-Galp, and 1,4-α-D-Manp, with branches of 1,4,6-α-D-Manp and 1,2,6-α-D-Galp. FMP-2 can stimulate phagocytosis and promote the secretion of NO, ROS, and cytokines like IL-6, IL-1β, and TNF-α in RAW264.7 cells ranging from 25 to 400 μg/mL. FMP-2 had great repairing effect on the immune injury of zebrafish induced by chloramphenicol. The phagocytosis ability of zebrafish macrophages and the proliferation of neutrophils can be greatly enhanced by polysaccharide FMP-2 with concentrations from 50 to 200 μg/mL. These findings suggest that FMP-2 might be used as a potential immunomodulator in the food and pharmaceutical industries.

Assessing Molecular Regulation of Vascular Permeability Using a VEGF-Inducible Zebrafish Model

Vascular endothelial growth factor (VEGF) stimulates vascular permeability in a variety of human pathologies, such as cancer, ischemic stroke, cardiovascular disease, retinal conditions, and COVID-19-associated pulmonary edema, sepsis, acute lung injury, and acute respiratory distress syndrome. Comprehensive investigation of the molecular mechanisms of VEGF-induced vascular permeability has been hindered by the lack of in vivo models that easily facilitate genetic manipulation studies in real time. To address this need, we generated a heat-inducible VEGF transgenic zebrafish model of vascular permeability. Here, we describe how this zebrafish model can be used to monitor VEGF-induced vascular permeability through live in vivo imaging to identify genetic regulators that play key roles in vascular barrier integrity in physiological conditions and human disease processes.

Cadmium significantly changes major morphometrical points and cardiovascular functional parameters during early development of zebrafish

Living organisms are commonly exposed to cadmium and other toxic metals. A vast body of research has shown the significant effects of these toxic metals on developmental processes. In order to study the role of toxic metals on early developmental stages of eukaryotes, we explored the effect of cadmium (Cd²⁺) contaminant on zebrafish. Thus, zebrafish embryos were exposed to 3 mg/L (16.7 μM) Cd²⁺ for 96 h and imaged every 24 h from the exposure onwards. Hatching rates of the eggs were determined at 72 h, followed by analyses at 96 h for: survival rate, morphometrical factors, and functional parameters of the cardiovascular system. Interestingly enough, significant hatching delays along with smaller cephalic region and some morphological abnormalities were observed in the treatment group. Moreover, substantial changes were noticed in the length of notochord and embryo, absorption of yolk sac with shorter extension, area of swimming bladder, as well as pericardium sac after Cd²⁺ treatment. Cadmium also caused significant abnormalities in heart physiology which could be the leading cause of mentioned morphological deformities. Herein, our results shine light on systematic acute embryological effects of cadmium in the early development of zebrafish for the first time.

Ovarian inseminated sperm impacts spawning success in zebrafish, Danio rerio (Hamilton, 1822) even in the absence of a male stimulus

Reproductive obstacles have led scientists to develop novel techniques/technologies for artificial reproduction. We aimed to investigate the possibility of propagating zebrafish females using sperm ovarian lavage with and without presence of male stimulus. This experiment consisted of several treatments: traditional spawning approaches with females and wild-type males (AB♀ × AB♂); no males present with non-manipulated females (AB♀); no males present with females inseminated with NaCl into ovarian lobes [AB♀(inj.NaCl)]; no males present with females inseminated with sperm from transgenic males into ovarian lobes [AB♀(inj.Tg♂)]; non-manipulated females kept separately from wild-type males (AB♀|AB♂); females kept separately from wild-type males and inseminated with NaCl into ovarian lobes [AB♀(inj.NaCl)|AB♂]; and females kept separately from wild-type males and inseminated with sperm from transgenic males into ovarian lobes [AB♀(inj.Tg♂)|AB♂]. There were no released eggs in both negative control treatments (AB♀ and AB♀|AB♂). Egg production increased (ranged from 0 to 28.5 eggs/female) when females were injected in the presence [AB♀ (inj.NaCl) |AB♂] or absence of male stimulus [AB♀ (inj.NaCl) and (AB♀(inj.Tg♂)]. A further increase in egg production [relative to AB♀, AB♀ (inj.NaCl), and AB♀|AB♂] was detected when females were inseminated with pooled sperm from transgenic males in the presence of male stimulus [AB♀(inj.Tg♂)|AB♂; ranged from 2.5 to 55 eggs/female] or when using traditional spawning approaches (AB♀ × AB♂; ranged from 25 to 131 eggs/female). Females inseminated with sperm produced embryos, although no differences were detected when females were inseminated with pooled sperm from transgenic males in presence (11.8 ± 16.3%) or absence (average = 12.6 ± 9.2%) of male stimulus. Traditional spawning approaches produced the most eggs (81.2 ± 42.3 per female) and highest fertilization rate (81.3 ± 10.4).

Recent development in zebrafish model for bioactivity and safety evaluation of natural products

The zebrafish is a species of freshwater fish, popular in aquariums and laboratories. Several advantageous features have facilitated zebrafish to be extensively utilized as a valuable vertebrate model in the lab. It has been well-recognized that natural products possess multiple health benefits for humans. With the increasing demand for natural products in the development of functional foods, nutraceuticals, and natural cosmetics, the zebrafish has emerged as an unprecedented tool for rapidly and economically screening and identifying safe and effective substances from natural products. This review first summarized the key factors for the management of zebrafish in the laboratory, followed by highlighting the current progress on the establishment and applications of zebrafish models in the bioactivity evaluation of natural products. In addition, the zebrafish models used for assessing the potential toxicity or health risks of natural products were involved as well. Overall, this review indicates that zebrafish are promising animal models for the bioactivity and safety evaluation of natural products, and zebrafish models can accelerate the discovery of novel natural products with potential health functions.

Effects of powdered activated carbon and calcium on trihalomethane toxicity of zebrafish embryos and larvae in hybrid membrane bioreactors

This study investigated the effect of powdered activated carbon and calcium on trihalomethane toxicity in zebrafish embryos and larvae in hybrid membrane bioreactors. Two hybrid membrane bioreactors were configured with the addition of powdered activated carbon or calcium to reduce the trihalomethane formation potential. Trihalomethane formation decreased by approximately 37.2% and 30.3% in membrane bioreactor-powdered activated carbon and membrane bioreactor-calcium, respectively. Additionally, the toxic effect of trihalomethane formation was examined on zebrafish embryos and larvae. About 35% of the embryos exposed to trihalomethanes (800 ppb) showed signs of deformation, with the majority displaying coagulation within 24 h after exposure. Color preference tests, which were conducted to identify any abnormal activities of the embryos, showed an increase in preference from short to longer wavelengths upon exposure to high levels of trihalomethanes. This may indicate damage to the optical organs in zebrafish when exposed to trihalomethanes. Behavioral analysis showed reduced mobility of zebrafish larvae under different trihalomethane concentrations, indicating a decrease in the average activity time with an increasing trihalomethane concentration. The membrane bioreactor effluents were toxic to zebrafish embryos and larvae in the presence of high trihalomethane concentrations. To understand the mechanism behind trihalomethane toxicity, further studies are needed.

Development of alternative and sustainable methodologies in laboratory research on sea urchin gametes

The aim of the present work is to develop a laboratory-scaled methodology for an on-demand supply of semen from the sea urchin Paracentrotus lividus. Firstly, sea urchin specimens were acclimatized to the long-term rearing in a recirculating aquaculture system and gonad maturation was obtained under controlled conditions. Semen samples were then collected from mature sea urchins and cryopreserved. Finally, post-thawing motility was evaluated, to verify whether the cryopreserved semen had maintained enough viability to be used in laboratory activities. The post-thawing motility parameters remained quite unchanged for up to 60 min after activation; moreover, the semen even retained the ability of motility activation for 60 min after thawing. This motility pattern makes the use of cryopreserved semen a feasible option in spermiotoxicity bioassays. The preliminary ecotoxicity test, carried out using motility parameters as endpoints, showed sensitivity levels to cadmium falling in the same order of magnitude as those recorded for fresh sea urchin semen and for cryopreserved sea bream semen. . Therefore, semen samples produced and stored according to the developed methodology described in this paper, can be considered a promising and sustainable alternative to those collected from mature sea urchins harvested in the field.

Plasticity of the skeleton and skeletal deformities in zebrafish (Danio rerio) linked to rearing density

The teleost zebrafish (Danio rerio), an established model for human skeletal diseases, is reared under controlled conditions with defined parameters for temperature and photoperiod. Studies aimed at defining the proper rearing density have been performed with regard to behavioural and physiological stress response, sex ratio and reproduction. Studies concerning the effect of rearing density on the skeletal phenotype are lacking. This study analyses the response of the skeleton to different rearing densities and describes the skeletal deformities. Wild-type zebrafish were reared up to 30 dpf (days post-fertilization) in a common environment. From 30 to 90 dpf, animals were reared at three different densities: high density (HD), 32 fish l^-1 ; medium density (MD), 8 fish l^-1 and low density (LD), 2 fish l^-1 . Animals at 30 and 90 dpf were collected and whole-mount stained with Alizarin red S to visualize mineralized tissues. The entire skeleton was analysed for meristic counts and 172 types of deformities. The results showed that the rearing density significantly influenced the specimens' average standard length, which decreased with the increase in the rearing density. Differences in meristic counts among the three groups were not observed. Rearing density-independent malformations affected the ribs, neural arches and the spines of the abdominal region, as well as vertebrae of the caudal complex. The HD group showed the highest number of deformities per specimen, the highest number of observed types of deformities and, together with the MD group, the highest frequency of specimens affected by severe deformities. In particular, the HD group showed deformities affecting arches, spines and vertebral centra in the caudal region of the vertebral column. This study provides evidence of an effect of the rearing density on the development of different skeletal phenotypes.

Enrichment for Laboratory Zebrafish-A Review of the Evidence and the Challenges

Simple Summary

The zebrafish is one of the most commonly used animals in scientific research, but there remains a lack of consensus over good practice for zebrafish housing and care. One such area which lacks agreement is whether laboratory zebrafish should be provided with environmental enrichment—additions or modifications to the basic laboratory environment which aim to improve welfare, such as plastic plants in tanks. The need for the provision of appropriate environmental enrichment has been recognised in other laboratory animal species, but some scientists and animal care staff are hesitant to provide enrichment for zebrafish, arguing that there is little or no evidence that enrichment can benefit zebrafish welfare. This review aims to summarise the current literature on the effects of enrichment on zebrafish physiology, behaviour and welfare, and identifies some forms of enrichment which are likely to benefit zebrafish. It also considers the possible challenges that might be associated with introducing more enrichment, and how these might be addressed.

Abstract

Good practice for the housing and care of laboratory zebrafish Danio rerio is an increasingly discussed topic, with focus on appropriate water quality parameters, stocking densities, feeding regimes, anaesthesia and analgesia practices, methods of humane killing, and more. One area of current attention is around the provision of environmental enrichment. Enrichment is accepted as an essential requirement for meeting the behavioural needs and improving the welfare of many laboratory animal species, but in general, provision for zebrafish is minimal. Some of those involved in the care and use of zebrafish suggest there is a ‘lack of evidence’ that enrichment has welfare benefits for this species, or cite a belief that zebrafish do not ‘need’ enrichment. Concerns are also sometimes raised around the practical challenges of providing enrichments, or that they may impact on the science being undertaken. However, there is a growing body of evidence suggesting that various forms of enrichment are preferred by zebrafish over a barren tank, and that enriched conditions can improve welfare by reducing stress and anxiety. This review explores the effects that enrichment can have on zebrafish behaviour, physiology and welfare, and considers the challenges to facilities of providing more enrichment for the zebrafish they house.

Involvement of dopamine signaling pathway in neurodevelopmental toxicity induced by isoniazid in zebrafish

AIMS

This study evaluated the neurodevelopmental toxicity of isoniazid (INH) in zebrafish embryos and the underlying mechanism.

METHODS

Zebrafish embryos were exposed to different concentrations (2 mM, 4 mM, 8 mM, 16 mM, 32 mM) INH for 120 hpf. During the exposure period, the percentage of embryo/larva mortality, hatching, and morphological malformation were checked every 24 h until 120 hpf. The development of blood vessels in the brain was observed at 72 hpf and 120 hpf, and behavioral capacity and acridine orange (AO) staining were measured at 120 hpf. Alterations in the mRNA expression of apoptosis and dopamine signaling pathway related genes were assessed by real-time quantitative PCR (qPCR).

RESULTS

INH considerably inhibited zebrafish embryo hatching and caused zebrafish larval malformation (such as brain malformation, delayed yolk sac absorption, spinal curvature, pericardial edema, and swim bladder defects). High concentration of INH (16 mM, 32 mM) even induced death of zebrafish. In addition, INH exposure markedly restrained the ability of the zebrafish autonomous movement, shortened the length of dopamine neurons and inhibited vascular development in the brain. No obvious apoptotic cells were observed in the control group, whereas considerable numbers of apoptotic cells appeared in the head of INH-treated larvae at 120 hpf. PCR results indicated that INH significantly raised the transcription levels of caspase-3, -8, -9, and bax and significantly decreased bcl-2 and bcl-2/bax in the zebrafish apoptotic signaling pathway. INH also markedly decreased the genes related to dopamine signaling pathway (th1, dat, drd1, drd2a, drd3, and drd4b).

CONCLUSIONS

Experimental results indicated that INH had obvious neurodevelopmental toxicity in zebrafish. Persistent exposure to INH for 120 h caused apoptosis, decreased dopaminergic gene expression, altered vasculature, and reduced behaviors.

Trichlorocarban induces developmental and immune toxicity to zebrafish (Danio rerio) by targeting TLR4/MyD88/NF-κB signaling pathway

Trichlorocarban (TCC) is ubiquitously detected in environmental matrices, while there is a paucity of information regarding its systemic toxicity. In the present study, we observed that TCC exposure led to high embryo mortality, delayed hatching and yolk absorption, as well as increased malformations, such as closure of swim sac and yolk sac edema. Meanwhile, TCC affected the formation and branch of subintestinal veins (SIVs), intersegmental vessels and posterior cardinal veins. Especially, the SIVs were shrunk, and their branches were reduced or even broken along with reduced coverage area. TCC-induced oxidative stress and excessive apoptosis resulted from abnormal expression of the anti/pro-apoptotic genes. Significant reduction in the number and aggregation function of immune cells proved that TCC had prominent immunotoxicity to zebrafish. TCC-targeted TLR4 signaling pathway was demonstrated by abnormal expression of the marker genes (tlr4, MyD88 and nf-κb) and release of the downstream inflammatory factors (TNF-α, IL-6, etc.). Inhibition of TLR4/MyD88/NF-κB pathway by an inhibitor (CA-4948) rescued the decreasing trend of the immune cells induced by TCC. Molecular docking results demonstrated that TCC could stably bind to TLR4 receptor to form hydrogen bonds and hydrophobic interactions with amino acids. Overall, these findings reveal the underlying molecular mechanisms on TCC-induced developmental and immune toxicity to zebrafish.

Long-term and in vivo assessment of Aβ protein-induced brain atrophy in a zebrafish model by optical coherence tomography

In this study, a neurotoxicity model of zebrafish induced by amyloid beta (Aβ) protein was developed and evaluated in vivo by optical coherence tomography (OCT). Aβ protein and phosphate buffer saline (PBS) were separately injected into the head of two groups of adult zebrafish (n = 6 per group). Congo-red staining results confirmed that Aβ protein had penetrated into brain tissue. All zebrafish were imaged with OCT on the 0th, 5th, 10th, 15th and 20th day postinjection. OCT images showed that PBS is not toxic to brain tissue. However, significant brain atrophy could be seen in the OCT images of zebrafish injected with Aβ-protein that was verified by histological consequences. In addition, zebrafish in the model group showed memory decline in behavioral tests. This study verified the feasibility of in vivo long-term assessment of Aβ protein-induced brain atrophy in adult zebrafish by OCT that has great potential to be applied in the neurological diseases research.

Silver nanoparticles: Toxicity in model organisms as an overview of its hazard for human health and the environment

Silver nanoparticles (AgNPs) have attracted remarkable attention due to their powerful antimicrobial action as well as their particular physicochemical properties. This has led to their application in a wide variety of products with promising results. However, their interaction with the environment and toxicity in live terrestrial or aquatic organisms is still a matter of intense debate. More detailed knowledge is still required about the toxicity of AgNPs, their possible uptake mechanisms and their adverse effects in live organisms. Several studies have reported the interactions and potential negative effects of AgNPs in different organisms. In this review, we report and discuss the current state of the art and perspectives for the impact of AgNPs on different organisms present in the environment. Recent progress in interpreting uptake, translocation and accumulation mechanisms in different organisms and/or living animals are discussed, as well as the toxicity of AgNPs and possible tolerance mechanisms in live organisms to cope with their deleterious effects. Finally, we discuss the challenges of accurate physicochemical characterization of AgNPs and their ecotoxicity in environmentally realistic conditions such as soil and water media.

Glis3 as a Critical Regulator of Thyroid Primordium Specification

Background: GLIS3 (GLI-Similar protein 3) is a transcription factor involved in several cellular processes. Homozygous mutations in the GLIS3 gene have been typically associated with neonatal diabetes and congenital hypothyroidism (CH) in a syndrome called NDH. NDH patients present developmental abnormalities including endocrine pancreas defects and a spectrum of thyroid abnormalities, mainly including thyroid dysgenesis (TD). The mouse models revealed a key role of Glis3 in pancreatic islets but not in early thyroid development, as Glis3 was described to retain a role in regulating thyroid hormone synthesis downstream the thyrotropin (TSH)/TSHR signaling pathway and in postnatal follicle proliferation. Hence, in this study, we have been taking advantage of the zebrafish model to gain insights on the Glis3 activity during thyroid organogenesis. Methods: Transient glis3-knockdown zebrafish embryos (called glis3 morphants) were generated by the microinjection of specific glis3 morpholinos at one- to two-cell stage to analyze the thyroid phenotype in vivo. Several additional analyses (in situ hybridization, immunohistochemistry, and pharmacological treatments) were performed for further molecular characterization. Results: The analysis of thyroid embryonic development revealed that Glis3 is involved in early steps of thyroid specification. glis3 morphants exhibited a reduced expression of the early transcription factors nkx2.4 and pax2a at the thyroid primordium level, which is not caused by changes in proliferation or apoptosis of the pharyngeal endoderm. As a result, the differentiated thyroid tissue in morphants appeared reduced in size with decreased expression of tg and slc5a5, a low number of thyroxine (T4)-producing follicles, associated with an elevation of tshba (homologous of the human TSHβ), thus resembling the clinical and biochemical manifestations of patients with TD. Interestingly, glis3 morphants have pancreatic β-cell defects, but not liver defects. In vitro and in vivo data also demonstrated that Glis3 is an effector of the Sonic Hedgehog (SHH) pathway. Molecular and pharmacological inhibition of SHH reproduced the thyroid defects observed in glis3 morphant. Conclusions: Our results demonstrate that glis3, within the SHH pathway, appears to determine the number of endodermal cells committed to a thyroid fate. This is the first evidence of the involvement of Glis3 in TD, thereby expanding the understanding of the genetic basis of thyroid development and CH.

Developmental toxicity of disinfection by-product monohaloacetamides in embryo-larval stage of zebrafish

As an emerging class of nitrogenous disinfection by-products (N-DBPs), haloacetamides (HAcAms) have been widely detected in drinking water. Limited toxicity studies have shown an inconsistent toxicity of monoHAcAms, including CAcAm, BAcAm and IAcAm. In this study, the developmental toxicity of monoHAcAms was evaluated in embryo-larval stage of zebrafish. Embryos were exposed to one concentration of 2.50, 5.00, 10.0, 20.0, 40.0 and 80.0 mg/L monoHAcAms from 4 h post-fertilization (hpf) to 120 hpf. Multiple endpoints, including hatching rate, morphological abnormalities, mortality as well as locomotor behavior were assessed at specified stages (24, 48, 72, 96 and 120 hpf). Results showed that 80 mg/L CAcAm and 40 mg/L BAcAm significantly decreased the hatching rate, IAcAm decreased the hatching rate and delayed the hatching process in a concentration-dependent manner with an EC₅₀ of 16.37 mg/L at 72 hpf. The frequency and severity order of morphological abnormalities increased with the raised exposure concentrations and prolonged exposure time, and the corresponding EC₅₀ at 96 hpf were 21.10, 9.77 and 16.60 mg/L for CAcAm, BAcAm and IAcAm, respectively. MonoHAcAms exposure resulted in a time- and dose-dependent response in mortality and the calculated LC₅₀ at 72 hpf were 38.44, 17.74 and 28.82 mg/L for CAcAm, BAcAm and IAcAm, respectively. Based on EC₅₀ for morphological abnormalities and LC₅₀, a toxicity rank order of BAcAm > IAcAm > CAcAm was observed. Different degrees of hyperactivity and hypoactivity were observed from locomotor behavior analysis in larvae from ≤10.0 mg/L monoHAcAms exposure groups. The light-dark periodic change was disappeared in larvae of 10.0 mg/L BAcAm exposure group. In summary, our study showed that monoHAcAms were developmentally toxic to zebrafish even at very low concentrations and BAcAm exerted higher toxicity than IAcAm and CAcAm. These results will further our understanding of the toxicity of HAcAms and its potential toxicological impact on human and ecological environment.

Effects of chronic prazosin, an alpha-1 adrenergic antagonist, on anxiety-like behavior and cortisol levels in a chronic unpredictable stress model in zebrafish (Danio rerio)

Post-traumatic stress disorder (PTSD) is often associated with significant neuroendocrine dysfunction and a variety of other symptoms. Today, there are limited efficacious treatment options for PTSD, none of which directly target the dysfunction observed with the hypothalamic-pituitary-adrenal (HPA) axis. The development of new pharmacological treatments is expensive and time consuming; thus, there is utility in repurposing compounds already approved for use in other conditions. One medication in particular that has shown promise for the alleviation of PTSD symptoms is prazosin, an alpha-1 adrenergic receptor antagonist used to treat hypertension. While there have been many studies indicating the efficacy of prazosin in the treatment of PTSD symptoms, no studies fully elucidate mechanisms elicited by this treatment, nor is it clear if prazosin normalizes neuroendocrine dysfunction associated with trauma exposure. The use of zebrafish (Danio rerio) has been growing in popularity, in part, due to the homology of the stress response system with mammals. In this study, the zebrafish model was utilized to determine behavioral and biological changes induced by chronic unpredictable stress (CUS) and how these effects could be modulated by chronic prazosin treatment. The results indicated that 7d of CUS increased anxiety-like behavior in the novel tank test and decreased basal levels of cortisol. Chronic (7d) prazosin treatment decreased anxiety-like behaviors overall but did not appear to affect CUS-induced changes in behavior and basal cortisol levels. This suggests that the clinical effectiveness of prazosin may not normalize dysregulated stress responses prevalent in many patients with PTSD, but that prazosin-induced relief from anxiety in stress-related conditions may involve an alternative mechanism other than by normalizing neuroendocrine dysfunction.

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

This study evaluates the embryotoxicity of dithienylethene-modified peptides upon photoswitching, using 19 analogues based on the β-hairpin scaffold of the natural membranolytic peptide gramicidin S. We established an in vivo assay in two variations (with ex vivo and in situ photoisomerization), using larvae of the model organism Danio rerio, and determined the toxicities of the peptides in terms of 50% lethal doses (LD₅₀). This study allowed us to: (i) demonstrate the feasibility of evaluating peptide toxicity with D. rerio larvae at 3–4 days post fertilization, (ii) determine the phototherapeutic safety windows for all peptides, (iii) demonstrate photoswitching of the whole-body toxicity for the dithienylethene-modified peptides in vivo, (iv) re-analyze previous structure–toxicity relationship data, and (v) select promising candidates for potential clinical development.

Preliminary safety assessment of oridonin in zebrafish

Context: Oridonin, isolated from the leaves of Isodon rubescens (Hemsl.) H.Hara (Lamiaceae), has good antitumor activity. However, its safety in vivo is still unclear. Objective: To investigate the preliminary safety of oridonin in zebrafish. Materials and methods: Embryo, larvae and adult zebrafish (n = 40) were used. Low, medium and high oridonin concentrations (100, 200 and 400 mg/L for embryo; 150, 300 and 600 mg/L for larvae; 200, 400 and 800 mg/L for adult zebrafish) and blank samples were administered. At specific stages of zebrafish development, spontaneous movement, heartbeat, hatching rate, etc., were recorded to assess the developmental effects of oridonin. VEGFA, VEGFR2 and VEGFR3 gene expression were also examined. Results: Low-dose oridonin increased spontaneous movement and hatching rate with median effective doses (ED₅₀) of 115.17 mg/L at 24 h post-fertilization (hpf) and 188.59 mg/L at 54 hpf, but these values decreased at high doses with half maximal inhibitory concentrations (IC₅₀) of 209.11 and 607.84 mg/L. Oridonin decreased heartbeat with IC₅₀ of 285.76 mg/L at 48 hpf, and induced malformation at 120 hpf with half maximal effective concentration (EC₅₀) of 411.94 mg/L. Oridonin also decreased body length with IC₅₀ of 324.78 mg/L at 144 hpf, and increased swimming speed with ED₅₀ of 190.98 mg/L at 120 hpf. The effects of oridonin on zebrafish embryo development may be attributed to the downregulation of VEGFR3 gene expression. Discussions and conclusions: Oridonin showed adverse effects at early stages of zebrafish development. We will perform additional studies on mechanism of oridonin based on VEGFR3.

Raising the Mexican Tetra Astyanax mexicanus for Analysis of Post-larval Phenotypes and Whole-mount Immunohistochemistry

River and cave-adapted populations of Astyanax mexicanus show differences in morphology, physiology, and behavior. Research focused on comparing adult forms has revealed the genetic basis of some of these differences. Less is known about how the populations differ at post-larval stages (at the onset of feeding). Such studies may provide insight into how cavefish survive through adulthood in their natural environment. Methods for comparing post-larval development in the laboratory require standardized aquaculture and feeding regimes. Here we describe how to raise fish on a diet of nutrient-rich rotifers in non-recirculating water for up to two-weeks post fertilization. We demonstrate how to collect post-larval fish from this nursery system and perform whole-mount immunostaining. Immunostaining is an attractive alternative to transgene expression analysis for investigating development and gene function in A. mexicanus. The nursery method can also be used as a standard protocol for establishing density-matched populations for growth into adults.

Drinking in the morning versus evening: Time-dependent differential effects of acute alcohol administration on the behavior of zebrafish

Alcohol (ethanol) abuse remains to be a leading cause of medical, including mental, problems throughout the world. Whether alcohol consumption leads to chronic use, and subsequent alcohol dependency and abuse is known to be influenced by the acute effects of this drug. Numerous factors may influence how alcohol administered acutely affects the individual. For example, the mechanisms engaged by drugs of abuse, e.g. cocaine as well as alcohol, have been shown to overlap with those underlying circadian rhythm, and conversely, the effects of these drugs may be dependent upon the time of day of their consumption. To investigate the interaction between circadian rhythm and alcohol, here we employ a simple vertebrate model organism that was previously successfully utilized in other aspects of alcohol research, the zebrafish. We expose zebrafish to alcohol for 20 min in the morning or in the evening, and analyze the effects of this treatment by comparing 1% (vol/vol) alcohol-treated and control (alcohol naive) zebrafish. We record numerous swim path parameters, and report, for the first time, that the time of day of alcohol administration differentially affects certain behavioral parameters, enhancing some while blunting others. Our results suggest a complex interaction between circadian dependent and alcohol engaged mechanisms, findings that represent both practical complications as well as opportunities for understanding how alcohol affects brain function and behavior of vertebrates.