Description of the individual growth of Daphnia magna (Crustacea: Cladocera) through the von Bertalanffy growth equation. Effect of photoperiod and temperature

Daphnia magna is a cladoceran used as a model organism in aquatic ecology and ecotoxicology studies. Because growth is a critical parameter to study the effect of environmental conditions on the development of zooplankters, the somatic growth of D. magna was measured here and described by the von Bertalanffy growth equation (VBGE), a mathematical model widely used in fisheries management. For this purpose, the effect of two temperatures (20 and 25°C) and two photoperiod conditions (12:12 and 16:8, light:dark) was assayed. Experiments began with neonate females and were finished when parthenogenetic females reached the age of 41 days; they were fed the microalga Ankistrodesmus falcatus (400,000 cell ml ^-1, 12 mg l ^-1, dry weight). According to the VBGE, maximal length (L _max) was inversely correlated with the growth rate (K). The highest L _max (6.45 mm) was for the females grown at 20°C with the 12:12 photoperiod, whereas the maximum growth rate (K = 0.182 ± 0.010) was for individuals grown at 25°C with the 12:12 photoperiod. The number of clutches during the studied period was significantly higher for females grown at 25°C, 12:12. Temperature affected the growth rate and the maximum size in D. magna; interaction of temperature with photoperiod was also noteworthy. The VBGE was a nifty way to assess the effects of the tested environmental factors.