We’re excited to share a new paper published in Biology Letters showing that long-term managed rearing does not erode key physiological tolerances in an extremophile fish. Using Poecilia mexicana from a hydrogen sulfide–rich habitat in southern Mexico, we tested whether traits critical for survival in extreme environments are lost after many generations in benign laboratory conditions.
Hydrogen sulfide (H₂S) is highly toxic and usually coincides with severe hypoxia. Fish from sulfidic habitats have evolved remarkable tolerance to both stressors, but replicating these conditions in managed care is impractical and unsafe. In our study, we compared wild-caught fish to laboratory stocks that have been maintained for ~40 generations without exposure to sulfide or low oxygen. We found that fish from the sulfidic population retained their high tolerance to both H₂S and hypoxia, with no evidence of major erosion under managed care. In some cases, laboratory-reared fish even performed as well as or better than wild-caught individuals.
These results suggest that key physiological adaptations to extreme environments can be genetically robust and persist under relaxed selection. For conservation, this is encouraging: assurance populations of sulfide spring fishes may retain traits essential for survival in the wild even when husbandry conditions do not replicate extreme habitats. More broadly, our findings support the feasibility of ex situ conservation for freshwater extremophiles, while highlighting the importance of evaluating multiple traits when assessing the conservation value of managed populations.
You can find the fill paper here: Williams et al. 2026. Resilient by nature: managed rearing does not erode physiochemical tolerances of an extremophile fish. Biology Letters.