Irradiating small animals used as fish food makes them bigger

THE WORLD’SRIKENRISSSL fisheries are overexploited. One way to relieve pressure on them is to increase the yield of fish farms. And one way to do that is to improve the quality of the food fed to the livestock in those farms. Abe Tomoko, of the Nishina Centre for Accelerator-Based Science, in Wako, Japan, has a novel proposal for doing this. In her role as director of the centre’s beam mutagenesis group, she has overseen the creation of 30 novel cultivars of crops and ornamental plants generated by the selective breeding of promising mutants created using radiation from a particle accelerator called the Beam Factory. This time, though, she has applied the technique to animals.The young of farm-raised fish species such as yellowtails, halibut, bream and bluefin tuna are fed with live prey. For the smallest fry these are often rotifers, a phylum of tiny animals discovered in the late 17th century by early microscopists. In particular, farmers use a complex of 15 species known collectively as . The members of this complex are, in turn, divided into three groups classified by size: , the adults of which are 170-190 microns long; , with adults 190-240 microns long; and , with adults 240-320 microns long. Members of these different groups are fed to progressively larger fish larvae.