A Bleedin' Octopus!

[Level_Head]

My apologies, folks from UK and Australia -- I don't mean it that way.

In videos that I've seen, octopus blood is rarely visible, and when it is it's not guaranteed to be distinct from an inking response to fear/injury. Even in videos showing cutting of live animals (ugh!), I understand that essentially no bleeding is visible. Is this an artifact of our poor vision?

Octopuses have apparently around 4% to 6% blood by body mass, and according to the paper below they have the ability to recover quickly from a loss of 40% or so of their blood using fluid filtered from their digestive tract. (Apparently, all of their water intake comes from this source; tie those ducts off and they quickly die of thirst.)

So -- is octopus blood ever visible in the water? Do body injuries have the "instant seal" effect that a lost arm has? Is that effect different by species?

This was the paper that talks about blood loss:
"FLUID UPTAKE AND THE MAINTENANCE OF BLOOD
VOLUME IN OCTOPUS"
http://jeb.biologists.org/cgi/reprint/175/1/211.pdf

A question that occurs to me: If they never lose blood, how did they evolve to be so good at replacing it?

Also, would blood in the water be visible to octopus eyes, with their much greater sensitivity to low light and polarization?

And how about the octopus's sense of smell? Can he smell the blood of another octopus?

 

[DWhatley]

From my understanding, all of the marine animals get their freshwater from what they eat (ie not an oddity of the cephalopods). I have tried multiple times to get some of our biology folks to explain why an octopus does not dehydrate with it starts fasting. GPO's are believed to fast for more than six months when they incubate their eggs. For those that will eat, it would seem freshwater crustaceans might be a good idea at this end point of their lives.

 

[Level_Head]

From my understanding, all of the marine animals get their freshwater from what they eat (ie not an oddity of the cephalopods). I have tried multiple times to get some of our biology folks to explain why an octopus does not dehydrate with it starts fasting. GPO's are believed to fast for more than six months when they incubate their eggs. For those that will eat, it would seem freshwater crustaceans might be a good idea at this end point of their lives.

I think there's a distinction to be made between "from what they eat" and "from seawater passing through their digestive tract."

Octopuses, apparently, produce about 9% to 12% of their body masses or thereabouts in urine every day. If the glands involved in that filtration are "ligated" (ducts closed) the animal dehydrates very quickly. But this is true whether they eat or not, it seems from the literature.

So, even a fasting, brooding mother is still filtering seawater from the digestive tract into pure water for the body -- or she's stopped 99% of urine and other waste production. I can see a great reduction of solid wastes, but metabolic wastes would still be happening I'd expect; she still has a metabolism.

I don't know if this gut-water filtration is more efficient or less when accompanied by eating -- it may not be much affected at all.

 

[Level_Head]

An update on octopus liquid intake: You know the old expression, "to burn a candle at both ends"? (It comes from Edna St. Millay's poem at the beginning of "A Few Figs from Thistles":

My candle burns at both ends; it will not last the night; but ah, my foes, and oh, my friends—it gives a lovely light!

This poetry reminded me of the octopus's short but remarkable life -- but there is another sort of peculiar connection.

The octopus apparently "drinks" from both ends. I was originally put onto this notion when I noted that in studies of blood and urine volume, they had to tie off the digestive tract at both ends. This paper mentions that, too, but also mentions the reason: "Rectal pumping":
http://jeb.biologists.org/cgi/content/abstract/145/1/215

Water Uptake in a Cephalopod and the Function of the so-called ‘Pancreas’ -- M. J. WELLS 1 and J. WELLS (Zoology Department, Cambridge, UK Laboratoire Arago, Banyuls, France)

If the gut of Octopus vulgaris is ligated at both ends, the animal loses weight at about 10% per day at 21°C, dying after about 48 h. Ligation of the ducts to the midgut gland has the same effect. If one or both ducts are cannulated and led to the exterior with a sufficient length of duct remaining, sea water is taken up by peristalsis and there is little or no weight loss. As body weight falls, blood and urine osmolality remain unchanged, but blood conductivity falls and blood copper concentration rises, indicating a loss of salts as well as water. Muscle dry weight, as a percentage of muscle wet weight, increases as body weight falls. Octopus is hyperosmotic compared with sea water and the rate of ultrafiltration through the branchial heart appendages into the kidney sacs is estimated to be sufficient to account for the observed body weight losses.

Each side of the midgut gland, connected to the gut by a digestive duct, includes two distinct structures. One, the digestive gland, produces enzymes and is also concerned with absorption of the fluid and paniculate products of digestion. The other, the digestive gland appendage (the so-called ‘pancreas’), is composed of cells with characteristics that strongly indicate bulk fluid transport; it seems likely that this is the principal site of the fluid uptake. This evidently includes salts as well as water, since sea water taken into the gut (notably by rectal pumping) is not concentrated as fluid is withdrawn.

The use of tubes proves that taking in water from the ocean does not require eating -- but we'd figured that out, I think.

Back to the topic:
I'm still hoping to hear from anyone who has ever seen octopus blood -- or knows definitively whether it's visible to humans.