THE mucky sediment below fish farms usually teems with antibiotic-resistant bacteria. The presence of such bacteria is a cause of increasing concern because resistance can limit the ability to fight diseases, but it is also not that surprising: pisciculturalists have a long history of dosing fish they are breeding and rearing with antibiotics. But some scientists suspect there is more to it than that. One group, led by Jing Wang of Dalian University of Technology in China, has found that the problem is also linked to what the fish are being fed.
Dr Wang knew from previous reports that fish farmers who had not used antibiotics for years, or had never used them at all, still had sediment in their marine farms carrying bacteria with many of the genes associated with drug resistance. The genes had to be getting into the bacteria somehow; one possible pathway was through antibiotic-resistance genes in fish food mingling in various ways with bacteria in the sediment.