Cephalopod Hydration

[DWhatley]

I have always been bothered by brooding octopuses' lack of food intake and hydration. The difference in the female when she broods and when the eggs hatch show the toll not eating takes but how does she get fresh water?

This line of pondering has made me reconsider procedures for thawing frozen foods. Freezing (especially in frost free freezers) removes most of the fresh water and I have recently changed to using fresh RO/DI water vs using new saltwater for thawing. The two octopuses I am currently keeping take the FW thawed at least as well as the SW thawed and I have seen no negative but possible (antecdotal and possibly unrelated) postitive response with skin color and levels of activity.

Any input on how cephs obtain freshwater if it is other than through their food?

Any ideas on how to determine if a ceph is dehydrated?

 

[ceph]

DWhatley,

Your question deserves its own thread.

One of the major challenges in cephalopod aquaculture has been the inability to find an acceptable frozen or prepared food for hatchling cephalopods. Cephalopods are extremely efficient at converting food to biomass. Adult and juv. cephs do just fine on diets of frozen foods but no species of hatchling thrives. Live foods such as mysids are expensive which makes raising cephs expensive. Most prior work has focused on nutrition, specifically loading up on protein and minimizing lipids but perhaps a new approach is needed. One thing that changes between hatchling cephs and juv and adult cephs is their surface area to volume ratio. That would effect the effort needed for osmotic regulation. . .

James

 

[DWhatley]

Your question deserves its own thread.

James,
It has occured to me that salinity might effect the hatchlings as well (especially the pelagic that stay closer to the surface where the water is more diluted with rain water) but I have never seen anything written up on their freshwater (I see you suggest they may do this directly through Osmosis) uptake. I also see that as they age they take on a bloated look, akin to water retention in humans when the regulatory system begins to break down (and we are put on low salt diets). I have read that fish get their freshwater from the foods they eat but are there any studies on cephalopods or octos specifically?

 

[ceph]

I'm really not sure. I don't think animals can regulate through osmosis - osmosis just doesn't work that way. There needs to be a "pump" of some sort in order to create a differential - like renal organs mentioned below. Otherwise everything reaches equlibrium with the surrounding water. Many inverts are osmoconformers - no pumps needed, internal salinity is more or less the same as sea water.

According to the ref below, cephs may somewhat regulate their internal osmotic pressure by selective excreting. Osmotic regulation would be a lot harder (energetically costly) for a soft squishy "leaky" animal with permeable skin than it would for an animal with a shell.

Cephs are also capable of a lot of behavior. I don't know that they detect and avoid low salinity but it would not surprise me to find out that they did. Most cephs have low tolerances for salinity change.

Perhaps the bloating is caused by the metabolic breakdown of protein in the body of older octopuses. Is there a metabolic biochemist in the house? If so, please chime in.

This older work is about all I could find. http://jeb.biologists.org/content/26/2/182.short There may be more relevant work out there that I am not familiar with. Most of my ceph physiology experience is with growth physiology.

James

 

[DWhatley]

Thanks for the paper James. Much of it was over my head but I could stay with the general comparisons of body fluid and sea water.

After struggling to get that cephs blood contains less salt as a percentage than what they eat the discussion confirmed I was getting that much:

While magnesium and sulphate are excreted in excess in the crustaceans, which have corresponding lower values of these ions compared with sea-water equilibrium values, sodium and sulphate are eliminated in the cephalopods, which have corresponding lower sodium and sulphate in their plasmas.

I had to laugh and pout when I found the following, easy to understand statement:

How far intake of fluid through the gut contributes to the salt and water balance of molluscs is unknown. It may play some part, but information on whether molluscs drink sea water to any extent is lacking.

I did pickup, however, that there is a pericardium (I know we do as well as it was removed in a family member) around the heart that they think acts as filtration and would seem to promote the possibilty some of my thoughts on the bloated look as they age.

Also the mention of elevated potassium might be a dietary consideration.