[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Daphnia and supplemental air

George wrote:
> > Non-member submission from ["Leng Yee" <lengyee at cheerful_com
> > I've just started a daphnia culture 2 days ago using live daphnia that 
> > I've purchased at a LFS. I'm feeding them wheat flour and so far it seems 
> > that some are surviving and congregating at the surface. However, I can't 
> Hi, Leng,
> Daphnia congregate at the surface practically ONLY when dissolved oxygen
> is low, assuming that they are NOT being poisoned! With a two-day
> culture it could be either cause.

I second that opinion.

> You probably overfed with the flour and created low oxygen level
> conditions. Contrary to general assumptions, Daphnia is a delicate
> species, that is why it is being used as a test animal for water
> pollution. It does NOT like water movement (as in aeration) nor rapid
> change in water parameters. 

Overfeeding a daphnia culture is very easy to do.  It almost always results
in oxygen deprivation.  However, I believe the notion that "daphnia cannot
tolerate aeration" is a misnomer.  I have found that one of the best ways
to stabalize a culture and prevent the described scenario is to add a
sponge filter.... the kind that do not require an airstone.

I believe the way this "aeration" folklore started was from people who
used airstones.  If you have fine bubbles in your culture, the air can
get lodged under the carapace of the organism.  While this does not seem
to directly harm them, they cannot swim very well and appear to starve to
death after being in this condition for an extended period.  If you use
a slow stream of course bubbles, you get the added benefit of healthy
oxygenated water with minimal detrimental affect.  You will notice that
a properly aerated daphnia culture will support a larger density of
daphnia as an added bonus!

I have also noticed that daphnia (at least the species that I own) will
die overnight if the pH drops below 5.  They seem to like the pH close
to neutral.  If you ever have a "crashed" daphnia culture, DON'T THROW
IT OUT!  Simply do a large water change (but leave the "mulm" on the
bottom).  The eggs resting on the bottom will hatch in the presence
of good water parameters.

David Robinson                          The Discus Page
robinson at ichips_intel.com               http://www.ee.pdx.edu/~davidr/