Resilient by nature: Managed rearing does not erode physiochemical tolerances of an extremophile fish

Populations in managed care are valuable resources that complement in situ
conservation efforts, but adaptation to captive conditions and other
domestication effects present concerns for conservation. Many populations
of fish adapted to sulfide springs are highly endemic and imperiled,
potentially benefiting from ex situ conservation efforts. However, it is
challenging to maintain natural conditions in the laboratory as hydrogen
sulfide (H2S) is highly toxic and coincides with severe hypoxia. Here, we
tested whether long-term standardized rearing of sulfide spring fishes
leads to the loss of H2S and hypoxia tolerances. We compared the
tolerances of Poecilia mexicana (Poeciliidae) from sulfidic and
non-sulfidic habitats that were reared in the laboratory for 18 years and
wild-caught fish from the same sites. Both H2S and hypoxia tolerances were
maintained in laboratory-reared fish from the sulfidic habitat.
Additionally, fish from a non-sulfidic cave site, evolutionarily derived
from a sulfidic population, exhibited higher H2S and hypoxia tolerances
than fish from the non-sulfidic surface site. While domestication can lead
to the loss of adaptations to extreme environmental conditions, our
research indicates this is not a concern in laboratory stocks of P.
mexicana, which retained tolerance of H2S and hypoxia despite not
experiencing these stressors for ~40 generations.