Scientists have grown large and fast-growing plankton by irradiating it with a beam of heavy ions

Economically important fish species such as bluefin tuna, yellowtail, flounder and groupers feed on plankton up to

until they get big enoughso that they can be fed artificial food. Rotifers, a type of animal plankton, are commonly used as a source of live food. However, as fish grow, they require increasingly larger baits, but rotifers tend to be small and often not large enough to satisfy the growing fish, leading to cannibalism or growth abnormalities and ultimately reduced survival.

"We decided to try to do something toimprove the survival rate of fish larvae as this will help improve aquaculture productivity. We thought that if we could create a large variety of rotifers using our experience, it would help stabilize aquaculture incomes."

Tomoko Abe from RIKEN RNC

Scientists began experimenting usinga technique known as heavy ion beam irradiation in an attempt to create larger rotifers. Heavy ion selection is a technique in which cells are exposed to a beam of heavy atomic nuclei, causing mutations much more efficiently than natural processes such as UV light. By adjusting the ion type and dose, the beam is used to induce random mutations in the genome, and strains with the desired phenotypes can be selected. The group has already succeeded in developing highly efficient mutant lines of oil-producing microalgae, high-yielding rice and commercial sake yeast using similar methods.

Using RIKEN RI Beam Factory (RIBF), the teamirradiated breeding rotifers with beams of argon and carbon ions. They then selected larger individuals and cultured plankton for several generations to create a large mutant line. The rotifers that were bred were about 1.2 times larger than the other lines, which the team thought would be the ideal size for raising young. They also found that some strains were not only larger, but also grew faster than the parent strains.

“In general, larger mutants grow slower than normal rotifers, but we were lucky enough to find a line that grows not only larger, but also faster.”

Tomoko Abe from RIKEN RNC

Food shortages due to population growthand increasing consumption is a serious global problem and countries around the world are looking for ways to increase food production. Resources from the ocean, which covers 70% of the Earth's surface area, can be an effective and promising solution to the problem. In particular, for Japan, as an island state with a large exclusive economic zone, increasing the extraction of marine resources is an attractive goal. The enlarged rotifers produced in this study have the potential to provide a stable supply of larger rotifers at a low cost, which is conducive to aquaculture development. Moving forward, the group now plans to use larger rotifers in field trials to see if they can demonstrate improved survival.

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