Zoospores of an Aphanomyces from a diseased fish ceased to be motile following physical shock, or ionic shock with 100 mg Ca l−1, but motility was regained after 4·5 h, without an intervening encystment phase. This novel finding indicates that, in this fungus at least, zoospores might be transported, immobile, by water currents and encyst only in response to conducive surfaces.
