Blind cave fish — most famously the Mexican tetra — have evolved in complete darkness and represent unique subjects for welfare research on sensory adaptation and pain.
Research into cave fish welfare raises important questions about whether absence of vision affects pain experience or stress responses. Studies suggest cave tetras have retained pain signalling pathways despite losing eyes, meaning research procedures that cause tissue damage remain ethically significant. In captivity, cave tetras kept in lit tanks may experience sensory discomfort compared to their natural dark habitat. Standard aquarium conditions can also fail to replicate the stable temperature and chemistry of cave environments.