Stenothermal

Stenothermal fish are adapted to a narrow thermal range and cannot tolerate significant temperature changes. Cold stenotherms (e.g. whitefishes, Arctic char, Antarctic icefish) are adapted to near-freezing water and die at temperatures above 10–18°C. Warm stenotherms (e.g. coral reef species) are adapted to constant tropical temperatures and are highly sensitive to even small temperature reductions. Climate change is particularly threatening to stenothermal species as they cannot easily relocate or adapt.

The bald notothen (Pagothenia borchgrevinki) is an Antarctic icefish that lives permanently under sea ice at −1.9°C. It dies at temperatures above 4°C — one of the most extreme cold stenotherms known.