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

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.