Fish and decompression.

[H2Andy]

When a deep water species is caught and brought quickly to the surface, the gas in the swim bladder expands much more quickly than the fish can release it. The membranes are very elastic and distend rather than bursting, pushing whatever is in their way through the point of least resistance, often the fish's mouth.

ya...

consider, however, the nautilus, which uses FLUID for bouyancy control (i.e. saltwater),
and can be brought up in nets quite quickly without ill effects

(they just squirt the water out)

 

[cowjazz]

For what it is worth...

Presbyterian Hospital in Dallas has a hyperbaric chamber. Dr. Jeffrey Stone heads up the hyperbaric medicine unit, and has a story he tells whenever he speaks to the local dive clubs.

A few years ago the Dallas World Aquarium flew in some leafy sea dragons for a new exhibit. Dr. Stone received a call from the aquarium. The caller informed Dr. Stone he had a bent fish, and was wondering if he would be willing to treat the fish. Dr. Stone thought is was a joke, and told them to come on down. Sure enough, the aquarium staff showed up with a bucket and a leafy sea dragon that was not looking so good. The fish was put in the chamber, taken down to 60ft, and immediately started to recover. The leafy sea dragon received a full treatment, and was returned to the aquarium in excellent health.

There is still a patient record in the Presbyterian Hospital system for Seadragon, Leafy.

 

[knotical]

I think the Doc is wrong on this one. I'm still trying to explain exactly why but I come up with only questions... If a parcel of water is saturated with nitrogen at the surface and then the parcel is pushed down into the deep, then is the mass of nitrogen must be removed from the parcel? I think not. The only way for the partial pressure of nitrogen to be constant regardless of depth would be for nitrogen to be released as a parcel of water is transported downward. How?

Similarly, in an upwelling event for the partial pressure of nitrogen to remain fixed, the mass of nitrogen would need to increase proportionatly with decreasing depth (in order to keep the partial pressure fixed) What is the source for this extra nitrogen that the water must acquire as it is upwelled?

I think that nitrogen is considered inert to most biological activities and thus conservative or close to it except maybe for nitrogen fixing bacteria?

Based on this type of logic I think fish can get bent.

However, once nitrogen molecules are dissolved in water, gas laws no longer apply. Recall the incompressibility of water and of its dissolved solutes, including nitrogen. Think concentrations, instead of partial pressures. Assume complete mixing and no other nitrogen addition or removal. The concentrations of solutes (including nitrogen) remain the same at any depth. Thus a chunk of water, whether enclosed in a fish or not, when brought from depth to the surface would be in nitrogen equilibrium with the atmosphere.

 

[The Chairman]

I think the Doc is wrong on this one.

Doc is correct. Fluid absorbs the pressure of gas it is exposed to. The entire ocean is only exposed to 1 atm and can ONLY absorb that much gas. If it had more internal gas pressure then the sea would boil (Just the dissolved gas, not the water).

 

[H2Andy]

The caller informed Dr. Stone he had a bent fish, and was wondering if he would be willing to treat the fish . . . . The leafy sea dragon received a full treatment, and was returned to the aquarium in excellent health.

There is still a patient record in the Presbyterian Hospital system for Seadragon, Leafy.

my guess is this was an O2 or CO2 problem "disguised" as a deco issue (remember, water is a non-compressible fluid: one gallon of water at the surface will contain the same amount of dissolved nitrogen than a gallon of water at 10,000 feet):


Seawater also contains small amounts of dissolved gases (nitrogen, oxygen, carbon dioxide, hydrogen, and trace gases). Water at a given temperature and salinity is saturated with gas when the amount of gas entering the water equals the amount leaving during the same time. Surface seawater is normally saturated with atmospheric gases such as oxygen and nitrogen. The amount of gas that can dissolve in seawater is determined by the water’s temperature and salinity. Increasing the temperature or salinity reduces the amount of gas that can be dissolved.

Once water sinks below the ocean surface, dissolved gases can no longer exchange with the atmosphere. The amount of gas in a given volume of water may remain unchanged, except by movement of gas molecules through the water -- diffusion (slow process), or by the water mixing with other water masses containing different amounts of dissolved gas.

In general, nitrogen and rare inert gases (argon, helium, etc.) behave this way - their concentrations are conservative and only affected by physical processes. In contrast, some dissolved gases are non-conservative and actively participate in chemical and biological processes that change their concentrations. Examples are oxygen and carbon dioxide -- released and used at various rates in the oceans, especially by organisms.

http://www.usask.ca/geology/classes/geol206/geol206rr2.html

 

[DivetheRock]

I think the right side of my head just exploded.
Guys, this is a lot of information. I can only assume that the Doc's explanation is correct. It sounds reasonable and logical to me. And, in the words of Homer Simpson "...[excuse me doctor, but] I think I know a little something about medicine."

 

[wedivebc]

I think the Doc is wrong on this one. I'm still trying to explain exactly why but I come up with only questions... .

No he is right. The dissolved nitrogen does not compress like a gas does so the partial pressure of nitrogen does not exceed 0.79ata even at depth.

 

[havnmonkey]

it's not DCS it's over expansion... is that what we can gather so far?

I think it also has something to do with the physiology of different types of fish. Those that spend most of there lives at greater depths might have a body that can handle the pressure at sea level, so the tissues themselves expand. Kind of like the cells of a wetsuit.

 

[H2Andy]

it's not DCS it's over expansion... is that what we can gather so far?

yup... as to fish being taken up too fast

i again repeat, the super-duper nautilus does not have this problem

(nautiluses rule!)

 

[dumpsterDiver]

No he is right. The dissolved nitrogen does not compress like a gas does so the partial pressure of nitrogen does not exceed 0.79ata even at depth.

I'm still trying to understand.