One of the hottest points of debate on aquaculture is the effect that farmed fish might have on their wild cousins. Fish raised in a major aquaculture operation live in close, sometimes cramped conditions that are nothing like the open ocean. As a result, they can become victims of disease and parasites—just as for centuries human beings who lived in densely populated cities tended to fall victim to infectious disease more often than those who lived in sparsely populated rural areas. Disease is a major economic worry for aquaculture producers—just as it is for their counterparts on land–but if infected farmed fish escape, they can introduce those diseases to wild species, with potentially devastating environmental consequences.

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