Competition
between the rotifer Brachionus rotundiformis and the ciliate Euplotes
vannus fed on two different algae
S.-H.
Cheng, S. Aoki, M. Maeda, A. Hino-2004
Aquaculture, 241(1-4): 331-343
Abstract:
The
ciliate Euplotes vannus is a common protozoan in mass cultures of
rotifers, and rapid reproduction of E. vannus occasionally reduces
the rotifer yield. We performed a competition experiment between the rotifer
Brachionus rotundiformis and the ciliate E. vannus. The
ciliate was inoculated at three stages of the rotifer growth curve: the lag
phase, the logarithmic growth phase and the stationary phase. When feeding
on the alga Tetraselmis tetrathele, the ciliate increased and the
rotifer growth was suppressed. The interference with rotifer growth was
stronger in the lag and stationary phases than in the logarithmic growth
phase. In contrast, when feeding on the alga Nannochloropsis oculata,
the ciliate did not increase and the rotifer growth was similar to the
control. In addition to the competition experiments, 15N
incorporation experiments were performed on the ciliate to investigate its
food preference. The nitrogen incorporation rates (% of body nitrogen h−1)
of the ciliate were 0.7% through dead algae and 1.9% through rotifer feces
when using T. tetrathele, and 0.4% through dead algae and 3.4%
through rotifer feces when using N. oculata. The incorporation rate
through bacteria-free rotifer feces was about one-third that of normal
rotifer feces. These results indicated that the ciliate did not incorporate
algal nitrogen directly, but rather through the microbial food chain, from
phytoplankton to rotifer feces to bacteria. E. vannus incorporated
the nitrogen of N. oculata and grew for a short time but the growth
was soon suppressed. This growth inhibition may be due to allelopathy of N.
oculata for E. vannus. Consequently, we propose that periodic
addition of N. oculata should control E. vannus, and that this
technique of applying allelopathy should be more sustainable than
conventional treatments.
(Biotechnology
Division, Taiwan Fisheries Research Institute, Tungkang, Pingtung 928,
Taiwan, e-mail of S. Aoki: asaoki@mail.ecc.u-tokyo.ac.jp)