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PT13 Aquatic Ecotoxicology I
(PT197) Evaluation of Factors Affecting Measurement of Daphnia magna Dry Weights.
Samel, A1, Hoke, R2, Bouchelle, L3, Green, J4, Dobrzynski, D5, Wetzel, J6, 1 DuPont Haskell Laboratory, Newark, DE, USA2 DuPont Haskell Laboratory, Newark, DE, USA3 DuPont Haskell Laboratory, Newark, DE, USA4 DuPont Haskell Laboratory, Newark, DE, USA5 DuPont Haskell Laboratory, Newark, DE, USA6 DuPont Haskell Laboratory, Newark, DE, USA
ABSTRACT- Studies were conducted to determine factors that could affect the precision of Daphnia magna dry weight measurements. The first experiment examined the effects of storage conditions on dry weight measurements. Pooled daphnid samples, dried at 700C for approximately 24 hours, were stored either in a dessicator or in the general lab area exposed to ambient humidity levels. It was determined that storage conditions did not significantly affect daphnid dry weight measurements. In addition, individual daphnids were weighed three times to determine within-daphnid variability and pooled daphnid variability. Measurement variability was greatest with individual weight measurements versus the pooled weight measurements, possibly due to the amount of handling of individual daphnids and the precision of the balance used during the experiment. A second experiment was conducted to further evaluate sources of variability first observed in the first experiment. Variation in daphnid dry weights associated with different individuals performing the dry weight measurements and a comparison of individual daphnid dry weight measures with pooled dry weight measurements were components of the second experiment. There was no apparent change in dry weights due to repeated dry weight measurements as observed in the first experiment. Measurement error, although high, was found to be approximately 33% lower than in the first experiment. Measurement error is still a significant factor and group dry weight measurements are recommended versus individual dry weight measurements. Paired comparisons among individual technicians performing dry weight measurements resulted in a significant difference in one of the three paired analyses. When conducting dry weight measurements it is important that either the same individual does all dry weight measurements or that effective training is provided to ensure minimum variability among personnel.
Key words: Dry Weight, Daphni magna, Variability
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