The scientists made the observation while assessing fish communities in a lake in southeastern Quebec last year. They found a zebra mussel attached to a lake chub (Couesius plumbeus), a species of minnow typically about 12 centimeters long. The observation, reported this month in Biological Invasions, is the only time a nonlarval freshwater bivalve has been seen attached to a fish. The mollusk had latched onto the hapless minnow (pictured above) using protein fibers called byssal threads, which they also use to attach to plants, rocks, and concrete.