The dual myths of the healthy wild fish and the unhealthy farmed fish.

Although diseases, suffering and death have always been recognized as intrinsic parts of life as far as humans are concerned, it seems that many people tend to disregard these factors when it comes to animals. In particular, wild fish are generally assumed to be 'healthy', although the public concept of that term is unclear. In contrast, farmed fish are often popularly viewed as 'unhealthy'. Present knowledge of the importance of epizootics among wild fish is clearly limited, especially regarding viral and bacterial diseases. In contrast to the popular view, the available data indicates that disease among wild fish is common, that epizootics may be of significant ecological importance, and that there is reason to believe that fish diseases among wild as well as cultured fish may be associated with reduced welfare. Large-scale aquaculture without prophylaxis is practically impossible without an unacceptable impact on the environment, as well as reduced fish welfare. In this essay, I oppose the traditional view that industrialisation of aquaculture is linked to reduced fish welfare. In contrast, modern industrial aquaculture with state-of-the-art prophylaxis probably represents a major improvement in controlling fish diseases, thus increasing fish welfare. This is true especially when compared to traditional third world aquaculture, as measured in terms of fish mortality and consumption of antibacterial agents. However, aquaculture may influence diseases of wild fish populations either by providing vectors for transmission of pathogens into new geographic areas, or by altering the balance in host-parasite dynamics by increasing the number of available hosts.