Movement of pathogens with the international trade of live fish: problems and solutions.

Inter-regional trade in live fish as eggs, larvae or juveniles provides the potential for parallel movements of pathogens. Pathogens that exist in a carrier state and/or can be transmitted by vertical means pose the greatest threat since casual observation, and even periods of quarantine or pathogen inspections, may fail to indicate their presence. Additional complications arise with the movements of non-target species for which health examinations may not be required, or for which criteria for pathogen inspections have not been developed. Although international trade in salmonids has been responsible for most of the disease regulations currently in place, an equal or stronger effort should be expected with other species. At the same time, ensuring equal treatment of all trading partners with respect to the level and sophistication of the health examinations to which the product will be subjected is a major problem. There are several examples of past and potential pathogen movements with fish or fish products. Unfortunately, these are often confused by a poor understanding of the current situation in the region into which the animal or product has been imported. The technology, experience or extent of surveillance in the importing region may be insufficient to assess the situation. Distinguishing between exotic imported pathogens and unknown pathogens which are already present in indigenous fish stocks can therefore often be difficult. The author discusses examples of clearly-documented imports of pathogens, as well as the potential for the spread of agents which pose an equal or greater danger. In addition, the author discusses the confusion which often arises when the background into which these pathogens are to move is poorly understood in the importing region.