 One key to good fish breeding is providing fish with the right food. That means getting the right-sized food. As fish larvae grow, so does the optimum size of their food. That's a problem for certain species bred in fisheries. Fish raised on live feed face a gap in their feed size as larvae. At a certain stage, the plankton they eat become too small for maximum growth. This food-size gap can affect the quality and value of fish raised for consumption. But researchers from Japan appear to have one solution, supersizing plankton with beams of heavy ions. Researchers from the Riken Nishina Center for Accelerator-Based Science generated high-powered beams of carbon and argon ions in the hopes of producing size-boosting mutations in rotifers, a phylum of plankton commonly fed to fish larvae. The tremendous amount of energy carried by these beams, a couple hundred thousand times the amount a human might receive during a routine CT scan, was enough to alter the DNA in rotifer cells. The result was a wide range of random mutations, the kind that would otherwise take ages to occur naturally. The hard part was determining which rotifers gained beneficial genetic mutations, namely mutations that led to rotifers that were not only larger than normal, but also that reproduced faster than normal. From among dozens of mutant lines, they narrowed down the beam settings that gave rise to significantly longer, wider, and faster multiplying rotifers. Importantly, the mutant rotifers preserved these qualities over several generations, at least five years worth. That means that accelerated ions could be a reliable way to introduce beneficial mutations into the rotifer genome, and it presents one solution for bridging the size gap in the diet of larval fish.