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RE: Notho fade away---is it the O2?

Hi Tyrone,

There is no doubt that temperature has a very significant impact on the
amount of air which can be disolved in water. But all of the experiments
which I am familiar with are done by saturating the water either by
agitation or forced aeration. Then measuring the oxygen level at a given
temperature. None include an active load on the system such as fish.

In the real world, although oxygen levels can not exceed the maximum
saturation level in still waters they most certainly can fall below maximum
saturation. Water depth, surface film, disolved solids and the density of
fish and other oxygen consuming organisms like fish can reduce the O2 level
in the water. If you can set up a fish tank in your lab and add some fish
then all you need do is increase the airation to see if there is a
measurable difference. If there is a difference we can not rule out that it
has an impact. If there is no measurable difference we can amend the theory
to water turbulance being the principal problem.

Given a lab and test equipment it is far from impossible to resolve the
question as to whether the real villan is aeration or agitation, or both.
But from a purely functional point of view, as these two variables occur
together (assuming that O2 level changes at all) in the home aquarium by the
amount of air which we pump in and or turning off the power filter.

Now all you need to do is convince your professor to let you play with his
toys for a while. Sounds like a plan.

Best regards,


-RJ-

-----Original Message-----
From: owner-killietalk at aka_org [mailto:owner-killietalk at aka_org]On
Behalf Of Tyrone Genade
Sent: Thursday, June 14, 2001 2:39 PM
To: killietalk at aka_org
Subject: RE: Notho fade away---is it the O2?


On 14 Jun 2001, at 14:30, -RJ- wrote:

> I do not have the test equipment required to answer your question but I am
> using just enough air now to drive a corner or air drive hang on filter. I
> use more air in larger tanks (10 gal or 15 gal) and very little in smaller
> ones (2.5 gal).

Unfortunetly that doesn't give an indication of howmuch O2 is in the
water... With the low saturation level of O2 in water not much
difference is made with violent or brisk aeration. IF the surface area
is large enough a body of stagnant water could be just as well
oxygenated as a body of moving water.
The only way to super saturate water with O2 is to put it under
pressure. Fast flowing mountain streams are saturated at 18 mg/ml
(If I have the right number). The average fish tank is at 26oC and
has between 14 and 16 mg/ml (I'm skating on thin ice here... I read
the values some years back and hope I'm recalling them properly).
The major governign factor for O2 content of water is actually
temperature rather than aeration. Many cool killies suffer in our
heated tanks not because of the heat but rather because of the
lower O2 levels. Many of their eggs fail to hatch for the same
reason. At the end of the day 2 mg difference is not a lot and I
would certainly not expect it to cause any problems.

At the end of the day what we need are numbers. We need
disolved O2 levels of the tanks we keep our nothos in. Unfortunetly
my Prof will never let me out of the lab with his expensive O2 meter
so my O2 levels will remain a mystery...

Bye
Tyrone Genade
Southern African Killifish Society Coastal & Offshore Coordinator
AKA 08248
tyronegenade at yahoo_com
http://www.geocities.com/tyronegenade

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P450 Lab, Biochemistry Department
University of Stellenbosch, 7602, South Africa
Ph: +27-021-808-5876, fax: +27-021-808-5863
**********************************************************

          In God I trust,
     but in all others I must have irrefutable proof!
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