The last decade was the hottest on record, and its consequences go far beyond melting glaciers. Climate change is disrupting ecosystems, threatening food security, and putting human health at risk. To address these complex challenges, scientists need research tools that are not only robust and predictive but also ethical and scalable. That’s where New Approach Methodologies (NAMs) such as zebrafish eggs come into play, offering powerful insights into how a warming world impacts life at every scale. But how can something as small as a fish egg help us tackle one of humanity’s biggest challenges?
Introduction
Studying climate change isn’t only about measuring carbon emissions or rising temperatures: it’s about understanding how these shifts cascade through living systems. According to the IPCC (Intergovernmental Panel on Climate Change), climate change is a lasting shift in the state of the climate, driven largely by human activities that alter the atmosphere (1). It manifests not only as warming, but also as altered rainfall patterns, more frequent extreme weather events such as heatwaves and storms, and changes in water quality and ocean chemistry. These combined stressors have unpredictable consequences for ecosystems, biodiversity, and ultimately human health. To prepare effective responses, whether through policy, conservation, or adaptation strategies, we need research models that can capture this real-world complexity in a way that is scalable, reliable, and ethical.
Zebrafish Eggs in Climate Research
This is where innovative biological models come in. Among the New Approach Methodologies (NAMs) gaining attention, zebrafish eggs stand out as a powerful model to study environmental change. As we’ve explored in a previous article, their rapid development, transparency, and shared biological pathways with humans make them ideal for observing how stressors like heat, pollutants, or changes in water quality affect living systems. Because they are scalable, cost-effective, and ethically preferable to traditional animal testing, zebrafish eggs provide a unique window into the cascading effects of climate change on biodiversity and, by extension, on human health.
Rising temperatures & heatwaves
Global warming is no longer a distant forecast, it’s a measurable reality. In 2024, the world recorded for the first time an annual average temperature more than +1.5°C above pre-industrial levels, a symbolic threshold that climate scientists have long warned about (2). Even a temporary overshoot of this threshold brings severe risks: more frequent and intense extreme events, irreversible biodiversity loss, and growing pressure on food and water systems.
One of the clearest signals of this warming is the surge in heatwaves: longer, hotter, and more frequent than ever before (3). These events stress ecosystems and species far beyond their natural tolerance ranges, with cascading consequences for agriculture, biodiversity, and human health. According to the World Health Organization, heat is now among the leading causes of weather-related mortality, especially affecting vulnerable groups like the elderly, outdoor workers, and those with chronic health conditions such as cardiovascular disease, diabetes, and respiratory illnesses (4).
Because zebrafish eggs are highly sensitive to temperature shifts, they offer a direct way to study the biological consequences of heat stress. Recent studies have shown that they reach adaptation limits around 37°C and cardiac failure near 38°C, with pollutants like phenanthrene blocking this adaptation and some drugs worsening heart damage (5). Another study found that early heat exposure changes gene activity and behavior later in life, showing how rising temperatures can leave lasting biological effects (6).
Pollution on the move
Climate change doesn’t only raise temperatures, it also changes how pollution spreads. Extreme weather events like floods and storms can wash contaminants into agricultural lands and water bodies, exacerbating food insecurity. As intense heat and drought become more common, crop failures are happening more often, putting farmers under increasing pressure, and prompting some policymakers to consider loosening environmental protections, such as pesticide bans, in hopes of “relieving pressure,” despite the long-term risks.
Zebrafish eggs offer a fast and transparent way to assess how pollutants affect living systems. Thanks to their conserved molecular pathways and physiology, which closely resemble those of humans, they have become an increasingly valuable toxicological model for uncovering mechanisms of toxicity and predicting potential health impacts.
Zebrafish have become a valuable model to uncover how pesticides affect early development. Research on the insecticide deltamethrin, widely applied in gardens, golf courses and mosquito nets, shows that exposure disrupts embryonic growth. Reported effects in zebrafish eggs include problems with swim bladder formation, behavioral changes linked to reduced acetylcholinesterase activity, and increased brain cell apoptosis (7). In adults, deltamethrin has also been associated with reproductive toxicity, as discussed in our previous article. Similar concerns arise with the neonicotinoid acetamiprid, which was recently the subject of regulatory debate in France. Studies demonstrate that zebrafish eggs exposed to acetamiprid develop spinal malformations, show lower hatchability and weakened movement, and suffer higher mortality rates at tested concentrations, clear signs of its harmful impact on survival and development (8).
Heavy metals such as lead, mercury, cadmium, and arsenic are naturally occurring elements, but human activities have dramatically increased their release into the environment. Unlike many organic pollutants, they do not degrade and instead accumulate in soils, water, and living organisms, where they can cause long-term toxic effects to both human health and biodiversity (9). Zebrafish eggs are a powerful model for assessing the toxicity of heavy metals under these shifting environmental conditions. A recent narrative review highlights how an exposure, even at environmentally relevant concentrations, disrupts development through mechanisms such as oxidative stress, impaired organ formation, and overall developmental delay (10). Studies on combinations of pollutants have further shown that when cadmium is present together with the acetamiprid, the effects on zebrafish larvae are intensified, leading to stronger growth inhibition and developmental abnormalities than when either pollutant acts alone (11).
Endocrine disruptors are chemicals that interfere with hormone systems, even at very low concentrations, and can affect growth, reproduction, and metabolism. With climate change altering how pollutants move and accumulate in ecosystems, the risks linked to these chemicals may intensify. In zebrafish eggs, exposures to compounds such as BPA, PFOS, and tributyltin (TBT) have been shown to disrupt metabolic pathways, clear signs of hormone-mediated effects even at sub-lethal levels (12). To complement zebrafish, researchers also use medaka eggs (Oryzias latipes), another small freshwater fish with a long history in toxicology studies. Medaka has been adopted into international regulatory frameworks through the OECD TG 251 (REACTIV) assay, which screens for estrogen activity, and OECD TG 252 (RADAR), which detects androgen disruption using transgenic embryos. Together, zebrafish and medaka provide fast, scalable, and standardized tools to identify endocrine-active pollutants and their effects on early development.
PFAS, or per- and polyfluoroalkyl substances, are highly persistent chemicals that spread easily through water and soil. Climate events such as floods can further accelerate their distribution. Zebrafish eggs are widely used to study their impact, with research showing developmental toxicity and changes in behavior even at low concentrations, as explained in our previous article.
Lowering the CO2 footprint in research
Global greenhouse gas (GHG) emissions, including CO2, continue to rise, with energy and transport as the main drivers (13). Research facilities also contribute, though their carbon footprint is harder to quantify. Available data suggest that plastics, equipment, and consumables account for over half of laboratory emissions, with a median of 2.7 t CO2 eq. per researcher annually (14). Animal labs are particularly energy-intensive, consuming up to ten times more energy per square meter than office space, mostly due to ventilation, cold storage and sterilization (15).
One powerful lever lies in the choice of experimental models. An EPFL study estimated that a single mouse breeding facility emits about 1,829 tons of CO2 per year, largely due to heavy reliance on gas for climate control (16). Zebrafish, in contrast, can be housed at 20 times the density in the same space, and their facilities run mainly on electricity. Thus, transitioning from mice to zebrafish could reduce CO2 emissions by around 1,737 tons annually, without sacrificing research capacity.
By combining scientific relevance with a lighter environmental footprint, zebrafish models not only help us understand the impacts of climate change, they also offer a more sustainable way to conduct the research itself.
Turning research into impact
For research on climate change to truly make a difference, it must be not only innovative but also reproducible, scalable, and ethical. Manual handling of NAMs such as zebrafish eggs remains time-consuming, prone to variability, and limits the throughput needed to capture the complexity of climate-related toxicology and ecology studies. This is where automation and standardization play a crucial role.
Our EggSorter was designed precisely to address these challenges. By improving accuracy in egg selection, it reduces by up to half the number of samples needed for reliable results. This means fewer animals are bred and maintained, lowering both ethical concerns and environmental impacts. Combined with the inherent efficiency of zebrafish compared to mice, where 20 times more animals can be housed in the same lab space, the impact is substantial, with automation contributing to an estimated 40-fold reduction in energy consumption and a significant cut in CO2 emissions for equivalent research outcomes.
With automation further optimizing throughput and minimizing waste, the EggSorter brings us closer to a vision of life science research that is not only more predictive and ethical, but also more sustainable.
Conclusions & outlooks
Zebrafish eggs and other NAMs offer powerful insights into how climate change and pollution affect living systems, but no single model can capture the full picture. We believe that the way forward is to combine NAMs with human data, explore multi-factor exposures that mirror real-world stressors, and extend studies to long-term and generational effects. With their transparency, rapid development, and scalability, zebrafish eggs are well-suited for this next step. As automation improves reproducibility and standardization, these tools can be more readily integrated into regulatory frameworks, ultimately helping to shape policies that protect both ecosystems and human health.
References
- IPCC, Annex I: Glossary, Reisinger, A., D. et al. In: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp. 119-130, doi: 10.59327/IPCC/AR6-9789291691647.002.Retrieved from https://www.ipcc.ch/sr15/chapter/glossary/
- Copernicus Climate Change Service, (2024). 2024 is the first year above 1.5 °C of warming over pre-industrial levels. Retrieved from https://climate.copernicus.eu/copernicus-2024-first-year-exceed-15degc-above-pre-industrial-level
- IPCC, Seneviratne, S.I., et al., 2021: Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change[Masson-Delmotte, V., et al.]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1513–1766, doi: 10.1017/9781009157896.013. Retrieved from https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-11/
- World Health Organization (WHO). (2023). Climate change and health: Heat and health. Retrieved from https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health
- Haapanen-Saaristo, A. M. et al., (2024). ‘Heat stress sensitizes zebrafish embryos to neurological and cardiac toxicity’. Biochemical and Biophysical Research Communications, 733, Article 150682. https://doi.org/10.1016/j.bbrc.2024.150682
- de Souza, A. M. et al., (2025). ‘Temperature effects on development and lifelong behavior in zebrafish’. Science of the Total Environment, 973, Article 179172. https://doi.org/10.1016/j.scitotenv.2025.179172
- Liu, C. et al., (2025) ‘The relationship between deltamethrin-induced behavioral changes and acetylcholinesterase activity in zebrafish embryos or larvae based on transcriptome’, Frontiers in Veterinary Science, 11. https://doi.org/10.3389/fvets.2024.1526705
- Ma, X. et al., (2019) ‘Developmental toxicity of a neonicotinoid insecticide, acetamiprid to zebrafish embryos’, Journal of Agricultural and Food Chemistry, 67(9), pp. 2429–2436. https://doi.org/10.1021/acs.jafc.8b05373
- Fisher RM, Gupta V. Heavy Metals. [Updated 2024 Feb 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557806/
- Manna, S. et al., (2025). ‘Unravelling the developmental toxicity of heavy metals using zebrafish as a model: a narrative review’. Biometals 38, 419–463. https://doi.org/10.1007/s10534-025-00671-z
- Hu, G. et al., (2023) ‘Combined toxicity of acetamiprid and cadmium to larval zebrafish (danio rerio) based on metabolomic analysis’, Science of The Total Environment, 867, p. 161539. https://doi.org/10.1016/j.scitotenv.2023.161539
- Ortiz-Villanueva, E. et al., (2018) ‘Assessment of endocrine disruptors effects on zebrafish (danio rerio) embryos by untargeted LC-HRMS metabolomic analysis’, Science of The Total Environment, 635, pp. 156–166. https://doi.org/10.1016/j.scitotenv.2018.03.369
- Ritchie, H.,et al., (2020) ‘Breakdown of carbon dioxide, methane and nitrous oxide emissions by sector’, Our World in Data. Available at: https://ourworldindata.org/emissions-by-sector (Accessed: 19 August 2025).
- De Paepe, M. et al., (2024) ‘Purchases dominate the carbon footprint of Research Laboratories’, PLOS Sustainability and Transformation, 3(7). https://doi.org/10.1371/journal.pstr.0000116
- Groff, K. et al., (2014) ‘Review of evidence of environmental impacts of animal research and testing’, Environments, 1(1), pp. 14–30. https://doi.org/10.3390/environments1010014
- Duranceau, A. et al., (2019). LCA of EPFL’s mouse animal facility: Executive summary. EPFL. https://www.epfl.ch/schools/sv/wp-content/uploads/2021/12/ACV_animalerie_2019_exec_summary.pdf
