Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 52 (2019)

Eﬀect of diﬀerent conditions of the mutant isolation system on rotifers
by using heavy-ion beam irradiation
K. Tsuneizumi,∗1 M. Yamada,∗1 K. Ichinose,∗1 H. Ichida,∗1 and T. Abe∗1
Heavy-ion beam mutagenesis is generally recognized
as an eﬀective method for mutation breeding.1,2) Although this method has been greatly successful withplants, its application to animals is limited. Therefore,
we plan to acquire more basic data to set up the optimal conditions for a heavy-ion beam irradiation system
by using Brachionus plicatilis sensu stricto (rotifer) as
the model.3)
In aquaculture, rotifers are used as the live bait forlarval ﬁshes that have just been born. As larval ﬁshes
grow, they select food based on the mouth size.4) Rotifers are used for larval ﬁshes at ﬁrst, and later on
the brown shrimp Artemia is used. Rotifers averagearound 300 µm in length, while Artemia is between
400 µm and 1 cm in length. When switching foodfrom rotifer to Artemia, a live bait of a suitable size
(300–400 µm) has not been found yet. During thisgap time, larval ﬁshes die of starvation or cannibalize
each other, and these problems result in a signiﬁcantdecrease in the number of larval ﬁshes. It is known to
be a common bottleneck in aquaculture.
In this study, to overcome the problem of starvation and cannibalization, we plan to establish large rotifers required during the gap time. Using heavy-ion
beams accelerated by the RIBF accelerator at RIKEN,
we measured the biological eﬀect of heavy-ion beamirradiation on rotifers under diﬀerent conditions. After irradiation, each rotifer was separated to a plastic
culture dish and cultivated at 20◦ C at a salinity of
1.8%. Nonirradiated rotifers almost survived throughthe experiment. On the contrary, the survival rate ofrotifers irradiated by 600 Gy of carbon-ion beam wasdecreased to 41.7% by the 16th day after irradiation(Fig. 1). The survival rate of rotifers irradiated by
200 Gy of argon-ion beam was decreased to 15.0% by
the 15th day after irradiation (Fig. 2). The survival
rate decreased gradually depending on the degree ofirradiation dose (Figs. 1, 2). These data will be helpful for the establishment of the mutant isolation systemby heavy-ion beam irradiation on rotifers.

Fig. 2. Eﬀects of diﬀerent argon irradiation conditions on
survival rate of rotifers. The rotifers were irradiatedwith argon-ion beams at diﬀerent dose levels (25, 50,
75, 100, 150, and 200 Gy). The survival rates weremeasured every two or three days under each conditionafter irradiation. The data includes mean ± SE of six
independent experiments. The bars represent the SE ofdata.

References
Fig. 1. Eﬀects of diﬀerent carbon irradiation conditions on
survival rate of rotifers. The rotifers were irradiatedwith carbon-ion beams at diﬀerent dose levels (100, 150,200, 300, 400, and 600 Gy). The survival rates weremeasured every two or three days under each condition
after irradiation. The data includes mean ± SE of six
independent experiments. The bars represent the SE ofdata.
∗1RIKEN Nishina Center- 221 -1) T. Abe et al., in Plant Mutation Breeding and Biotechnology, edited by Q. Y. Shu et al., (CABI, Oxfordshire,2012).
2) A. Tanaka et al., J. Radiat. Res. 51, 223 (2010).
3) S. Mills et al., Hydrobiologia 796, 39 (2017).
4) Y. Sawada et al., Bull. Fish. Lab. Kinki Univ. 7, 1(2000).