Study
Hypoxic survival strategies in two fishes: extreme anoxia tolerance in the North European crucian carp and natural hypoxic preconditioning in a coral-reef shark
Nilsson, Göran E.; Renshaw, Gillian M. C.
Journal of Experimental Biology, 2004
Compared how a freshwater fish that survives months without oxygen and a reef shark that experiences nightly hypoxia handle low oxygen, measuring metabolic rate, brain function and end products.
- Studied in
- Carassius carassius, Hemiscyllium ocellatum
- Sample size
- two species under controlled oxygen regimes
Crucian carp survive months of complete anoxia in ice-covered ponds by converting lactate to ethanol and excreting it across the gills, avoiding the acid build-up that kills other fish. The shark instead uses repeated mild exposure as preconditioning.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
There are distinct routes to hypoxia survival, and the crucian carp’s ethanol pathway is unique among vertebrates.
How NatureHQ reads it
The ethanol result is the memorable one and it is real: the fish’s solution to the acid problem is to make its waste product volatile and breathe it out. NatureHQ pairs it with the turtle’s shell-buffering as two answers to the same difficulty.
- Two species chosen as extremes; they are not representative of fishes generally.
- Laboratory anoxia is imposed more uniformly than the seasonal anoxia of a frozen pond.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Hypoxia tolerance
Animals that survive months without oxygen do not carry a bigger store of it. They cut demand almost to nothing, protect the brain deliberately, and deal with the acid their anaerobic metabolism makes.
Hypoxia tolerance
The months-without-oxygen records belong to cold animals. The same turtle or carp at summer temperatures survives a small fraction of that — the cold is part of the mechanism, not the setting.
Published by: The Company of BiologistsPublished by The Company of Biologists.
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-03.