The spread of diseases between regions is usually through the movement of live
animals (Hedrick, 1996). Although movement of diseased fish is unlikely to be legal, low
prevalence of clinical disease and subclinical infections might go undetected (Murray and
Peeler, 2005). Since wild fish also can transport pathogens, it is difficult to control these
pathogens in public rivers. Moreover, pathogens can be transported in association with using
the same equipment. Most fish farmers use the same hand net to remove sick or dead fish.
Fish in cages have also been reported to transmit pathogens to other cages and to wild fish
over vast distances (Chambers & Ernst, 2005).