Science Buddies: "Ask an Expert"

Hi,
My name is Allie Agnew and this year, I am conducting a science fair project about the effect of Caffeine on the Daphnia Magna’s heart rate. I have been looking high and low, for the weight of daphnia. It is crucial in my research. If you happen to know the answer to this question, or know anybody who would know, please inform me!
Thanks,
Allie
4067

I'm not sure there's any one answer here. It will depend on the size of the specific animals you have. When you ask the question in Google you find a few different answers.

http://link.springer.com/article/10.1007%2FBF00772684 is a link to a study done by Kees Kersting and Corrie van der Leeu-Leegwater on the effect of food concentration on respiration of daphnia magna. To get the whole study you have to buy it, but it includes:

The mean body length of animals used in subsequent experiments of the study varied from 2.5 to 3.1 mm, and the mean length of all animals was 2.6 mm. The mean weights varied from 0.112 to 0.164 mg with a mean of all experiments of 0.138 mg.

http://www.aslo.org/lo/toc/vol_17/issue_4/0645.pdf gets you a paper done by researchers in Italy who reported the dry weight (more reliable, but you have to sacrifice the animals to get it).

Other people have asked the same question and got pointed towards a research paper that seems to be hard to find now, but the discussions of the question include the table. http://www.madsci.org/posts/archives/20 ... .Zo.r.html and http://kaimukirip.k12.hi.us/MSPShareWeb ... Study.html

If you wanted to measure it yourself, you could take a sample of your colony in water and weigh that, then strain out the animals and reweigh the water. That gives you the weight of the animals. Count them and divide to get the average weight of the specific individuals you have. It does appear that the weights can vary a good deal depending on size.

Howard