Lifetable demography and population growth of the rotifer Brachionus angularis in Kenya: influence of temperature and food density

Abstract

Lifetable demography and reproductive traits of a Kenyan strain of the rotifer Brachionus angularis were investigated using individual and small batch culture approaches. The rotifer was identified morphologically before conducting studies at 20, 25 and 30 °C, using Chlorella vulgaris at 2.5 × 105 to 2.5 × 107 cells ml–1. The rotifers were highly fecund, producing 2.11 ± 0.07 offspring female–1 day–1 and reproductive, producing 8.43 ± 0.24 offspring female–1 at 25 °C with 2.5 × 106 algal cells ml–1. The highest intrinsic rate of natural increase (0.74 ± 0.02 d–1), specific population growth rate (0.49 ± 0.01), longest life expectancy at hatching (12.41 ± 0.28 d) and shortest generation time (2.87 ± 0.03 d) also occurred at 25 °C with 2.5 × 106 algal cells ml–1. The duration of hatching to first spawning was shortest (2.86 ± 0.21 h) at 30 °C with 2.5 × 107 algal cells ml–1 and longest (8.83 ± 0.39 h) at 20 °C with 2.5 × 105 algal cells ml–1. The highest population density (255.7 ± 12.6 ind. ml–1) was realised at 25 °C with 2.5 × 106 cells ml–1 on Day 8, whereas the lowest population density (122.0 ± 3.6 ind. ml–1) was realised at 20 °C with 2.5 × 105 cells ml–1 on Day 8. The lorica length and width of the Kenyan strain of B. angularis are 85.6 ± 3.1 µm and 75.4 ± 3.6 µm, respectively. The rotifer optimally reproduces at 25 °C when fed with 2.5 × 106 algal cells ml–1.