GROWTH, REPRODUCTION AND POPULATION GROWTH FORM OF DAPHNIA MAGMA STRAUS

Daphnia magna Straus, derived from a pure strain and aged 6±6 hours, were reared under renewed static condition at 25±1℃. Animals were divided into two groups and fed with Scenedesmus obliquus about (4×105 cell, ml-1) and Chlorella pyrenoidosa (6—8×105 cell. ml-1), respectively. Population parameters regarding growth, longevity, fecundity and population increase were recorded throughout their life-span. The results are summarized as follows:1. The growth of bedy-length (lt, in mm) in relation to age (t, in day) may be described as lt=4.57—3.518e-0.0838t for animals fed on Scenedesmus, and lt=4.00—1.945e-0.0763t for those fed on Chlorella.2. The mean longivity of the individuals fed on Scenedesmus was estimated to be 68.40±9.82 days or 27.5±2.88 instars. The instur(x)-age(t) relationship is given approximately as t=—2.245+1.510x+0.035x2 (r=0.99, Pt)for individuals ranging from 2.5 to 4.0 mm in length was found to be curvilinear and the equation is expressed as: lg y=2.65 lg 1-0.04 (r=0.975, Pm) as computed from the tables is 0.454 per female per day; the net reproduction rate (Ro) is 448.396 per generation and the mean length of a generation (T) is 28.12 days.5. In a population originated by 10 individuals, the population growth curve of D. magna was shown to be logistic anal may be expressed as y=(4,400)/(1+e3.86-0.131t, in which y denotes total individuals and t, days.