species of the day: Champsocephalus gunnari

[eub]

Chosen semi-arbitrarily as a representative of the Antarctic icefish family, Channichthyidae, who lack hemoglobin. "Semi-" because it goes some one better in lacking myoglobin, too.

"Preliminary observations on the heart of the haemoglobinless Antarctic fish Champsocephalus gunnari, Lonnberg":

The heart of the haemoglobinless and myoglobinless "icefish" Champsocephalus gunnari shows interesting morphometric and histological features.

"Variable expression of myoglobin among the hemoglobinless Antarctic icefishes":

Of the eight icefish species examined, three lack Mb polypeptide in heart ventricle, although one of these expresses the Mb mRNA. All species of icefish retain the Mb gene in their genomic DNA. Based on phylogeny of the icefishes, loss of Mb expression has occurred independently at least three times and by at least two distinct molecular mechanisms during speciation of the family.
[...]
Pale coloration of icefish tissues has led most researchers to assume that Mb is not present in icefish oxidative muscles (3-7). However, we collected three channichthyid species off the Antarctic Peninsula, Chionodraco rastrospinosus, Pseudochaenichthys georgianus, and Chaenodraco wilsoni, that displayed distinctly rose-colored hearts.

(Why do they lack hemoglobin? Water's unaided gas solubility is better down there, but clearly not as good as they'd like. I think (after changing my mind) that this is saying that hemoglobin delivers oxygen poorly at low temperatures, but is it worse than nothing, or just not worth the synthesis?)

Comments

[aquaeri.livejournal.com]

I think myoglobin is basically a secondary, muscular oxygen store. I remember whales have an enormous amount of it, allowing them to go for half-hour dives.