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Re: Live Foods Digest V2 #212

The presence of large amounts of ammonia retards growth in a lot of
organisms and daphnia are no exception, but the slow/little movement tends
to suggest the presence of nasty ions in the water, usually metals from
pipework or the treatment works. There are really a lot of possibilities
here, and it could be as simple as a build up of waste metabolites in the
water (usually the water gets a brown tint to it after a while when they
get into high concentrations). I did an experiment recently (sadistic
bugger that I am) and didn't change the water in a 20 litre magna tank for
3 weeks. Only water I changed was a litre of water for every litre of
green I put in. Fed every day, the population exploded after a few days,
reached a peak at about 17 days, and then dropped like a hot potatoe to
slightly more than 0 live daphnia at the end of 3 weeks, simply from
metabolite build up in the water.

Good thing to remember is that water testing companies/institutions often
use young D. magna (less than 24 hours old) to test water for metal ions
and certain other toxic substances. The tests are measured in
two ways - a percentage of the Daphnia lose mobility and/or
heartbeats will be measured (you'd be surprised how many times a 
minute a Daphnia's heart beats).


John

> 
> Date: Fri, 02 Oct 1998 09:29:18 GMT
> From: spflume at gwdg_de (Stephan Pflume)
> Subject: Re: Live Foods Digest V2 #211
> 
> On Thu, 1 Oct 1998 15:58:01 -0400 (EDT), Owner-Live-Foods at actwin_com
> (Live Foods Digest) wrote:
> 
> >Your green water pH problem probably stems from the starting pH of the
> >water, the dissolved salt content and the ammonia levels (I guess you know
> >that though). As long as you keep the ammonia levels down, D. magna and D.
> >pulex can do well at anything up to 9 from what I can tell. If only
> >ammonia didn't change in toxicity with pH :(.
> 
> Hm. I haven't measured anything. I just tried to rear Daphnia magna in
> an outdoor tank, which had become green during some weeks before. Well
> though these stayed alive, they became rather lucid and reproduced
> rather slow. 
> 
> Stephan
> - -- 
> Stephan Pflume
> Abt. Vegetationskunde und Populationsbiologie
> Wihlelm-Weber-Str 2. 37075 Goettingen
> 
> ------------------------------
> 
> End of Live Foods Digest V2 #212
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