Study
When bad things happen to good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes
Sidell, Bruce D.; O'Brien, Kristin M.
Journal of Experimental Biology, 2006
Reviews the evidence on why icefish lack haemoglobin and, in some species, myoglobin, and whether the loss confers any benefit or is tolerated rather than favoured.
- Studied in
- Channichthyidae
- Sample size
- review of the icefish family
The evidence indicates loss without compensating advantage: icefish sustain oxygen delivery through very large hearts, high blood volume and low metabolic demand, at considerable circulatory cost. The loss is best explained as tolerated in a cold, oxygen-rich, low-competition environment rather than as an adaptation.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The absence of haemoglobin is a disaptation retained because the Southern Ocean permitted it, not an improvement.
How NatureHQ reads it
The record that keeps NatureHQ from writing that icefish evolved clear blood to cope with the cold. The current reading is close to the opposite, and it is a good demonstration of the adaptation page’s point that a trait present in an extreme environment need not be an adaptation to it.
- The argument is comparative and physiological rather than experimental; the counterfactual cannot be tested.
- Whether myoglobin loss in some species carries a benefit remains debated.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Icefish
Antarctic icefish have no haemoglobin and colourless blood. The evidence points to a loss they got away with in cold, oxygen-rich water — not an improvement, and not an adaptation to the cold.
Icefish
No advantage to lacking haemoglobin has ever been demonstrated in icefish. The suggestion that thinner blood is easier to pump in the cold is a hypothesis, and the compensations the fish maintain are expensive.
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.