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Re: Live Foods Digest V2 #102

Scott Davis wrote:
> Date: Sat, 18 Apr 1998 00:30:32 -0500
> From: Scott Davis <UncleScott at prodigy_net>
> Subject: Daphnia temperatures
> Hi all,
>         A more legitimate question.... In other conversations with a friend
> from Florida, he mentioned that his Daphnia "pulex" never did well at
> warm temperatures or well below 50 degrees F. The so called pulex that I
> have had around for the last 17 years doesn't do well in warm
> temperatures either. However it will do very well at 50 degrees and will
> even thrive under a couple of inches of ice if there is not too much
> organic debris under that ice sucking up the free oxygen. (It is no fun
> harvesting it then though!)
>         Part of the problem is that what we are calling pulex (or magna for
> that matter) in different parts of the U.S. and elsewhere may not be the
> same creature. What temperatures do your so called pulex do well at?
>                                 Thanks,
>                                 Scott
> PS: It is great to see George S. holding forth. George, anything you get
> involved with gains a touch of class!

Hi, Scott,

First of all, thank you for your kind words!

You are probably right that the different Daphnia "pulex" that people
keep are not one and the same critter. Whether they are different
species, or just a different race or strain, I can't tell, but they
certainly are not all the same. 

First of all, the taxonomy of Daphnids is in a flux (if you thought that
killie nomenclature is a mess, try Daphnia!). The uncertainty is partly
due to the fact, that Daphnia change their morphology in response to
environmental conditions. For instance, heir shape can change in the
presence or absence of predators (excluding killie keepers), etc. Some
clones of Daphnia have been shown to change the shape of their "hood" -
a taxonomic marker, etc.

Research in Scandinavia has shown that "identical" Daphnia from two
pools, only yards apart, have different electrophoretic "bands" - which
could mean a different species, or a different race,or .... the same old
Daphnia, just a different individual. (Because Daphnia are
parthenogenetic, all their progeny are a clone of the mother. If two
different individuals (mothers), of the same species, each started their
colony in a different pool, the result could be what we find in nature.
It just adds to the general confusion.

As to my Daphnia, they live, comfortably, at 18-22 C (64-72 F). Before I
installed AC, temperature used to go up over 25 C (77 F) and the Daphnia
did poorly. Ceriodaphnia (dubia?), on the other hand, is doing well at
25 C, not so good at below 18 C.
While all the Daphnia that I am familiar with are primarily cold-water
critters, there just has to be a tropical species of Daphnids that can
live and multiply in water over 30 C (85 F). Wouldn't it be nice, if 
people who are traveling to exotic spots to collect fish, would also
look for warm-water Daphnia!?

If you get several responses at what temperature people keep their
Daphnia, please let me know.