The importance of maintenance conditions of Daphnia magna Straus as a test organism for ecotoxicological analysis

Abstract

Insufficient attention to the standardization of conditions for test organisms can lead to a distortion of bioassay results by changing the characteristics of the culture. The present study deals with the influence of abiotic factors (temperature of cultivated water, its chemical composition, season of the year) and biotic factors (seeding density) on the culture of Daphnia magna Straus. The natural mortality of D. magna is described by the Gompertz equation. One of the parameters of the equation related to daily increase of mortality is very stable, and we suggest monitoring its constancy as a sign of the health of D. magna culture. Seeding density of crustaceans affects both the fertility of species and their mortality. We observed a high degree of compensation for the natural death of adults with increasing fertility for groups of 10 and 25 species living in 1 L of water; the current population density of D. magna regulates the birth rate of juveniles. If the density is 50 individuals/L, the compensatory effect is reduced. Keeping Daphnia in small groups (for example, 10 individuals) and an increase in temperature from 20 to 25 °C reduces the average life expectancy. Therefore, when choosing a test protocol to determine chronic toxicity, it is important to pay attention to the seeding density of Daphnia, the optimal value being approximately 25 individuals/L. Sensitivity of D. magna depends on the season: it is maximal in winter and minimal in spring and summer. In addition, crustaceans' sensitivity increases when they are kept in water with low content of natural salts. Environ Toxicol Chem 2018;37:376-384. © 2017 SETAC.

In Situ and after Synthesis of Magnetic Nanoarchitectures Grown onto Zeolite Type 5A/CTAB Frameworks and Their Ecotoxicological Properties

“…D. magna populations were grown on a standardized medium under laboratory conditions and were kept at 20 ± 2 °C under an 8 h light and 16 h dark photoperiod ratio at a pH of 7.5 ± 0.5 . The cladocerans were fed everyday with 0.5–0.8 mL of microalgae according to their life stage and number of organisms per culture medium.…”

“…After each exposure, surviving organisms were transferred to an NPs-free culture medium and maintained for the subsequent 14 days but fed daily with 0.3 mL of microalgae. Every day, survivors and neonates of the next generation were counted to calculate the reproduction rate and to evaluate the mean lethal concentration value (LC 50 ), which is the main parameter generally used for evaluating ecotoxicological bioassays …”

Intraspecific Sensitivity to Toxicants – a Methodological Problem of Bioassay: Review

“…The most likely reasons for such interlaboratory differences in individuals of the same species are differences in the chemical composition of cultivation waters, nutrition of organisms, cultivation protocols (density of model populations, temperature of keeping and temperature of the experiment, total volume of the cultivation medium, frequency of manipulations, etc. ), on which detailed studies are available [Olkova et al 2018;Terekhova et al 2018].…”

“…In the earlier work [Olkova et al 2018], it was shown that the density of model cultures of test-organisms affects the lifespan and fertility of D. magna -these are the parameters the variations of which are assessed when determining the toxicity of the test medium. Confirmation of this hypothesis can be seen in the work devoted to the effect of the pesticide on the dragonfly larvae Ischnura elegans under the conditions of competition between individuals and in their individual, isolated, keeping.…”

“…Bioassay under tightly controlled conditions using standard test-cultures improves the accuracy and reproducibility of toxicological assessments. There are the following difficulties in bioassay standardization: stock and supply of standard materials, storage stability of the standards, criterion of acceptance [Asano 2006], selection of cultivation water, variety and quality of test-cultures, standardization of test conditions [Olkova et al 2018;Terekhova et al 2018]. These issues can be solved through development of international bioassay protocols and introduction of additional criteria for the quality of test-cultures [Olkova 2021].…”