How do you tell if a salmon is fit and well? This is a question, which has troubled salmon farmers and biologists for years, but now scientists may have come up with the answer - using DNA chips. By studying the genes of Atlantic salmon, scientists are developing a DNA chip to monitor the health and performance of salmon, a tool that could both save the salmon industry thousands of pounds and also help conserve dwindling wild salmon populations. Atlantic salmon is a disappearing species in the wild. They are particularly vulnerable to infection because of the dramatic physical and chemical changes they go through, known as smoltification, which enable them to live in both fresh and saltwater. Assessing their health and performance is very difficult as conventional measures used in other animals, such as temperature, blood protein levels and general demeanor, are not relevant or are difficult to assess in fish. Farmers and conservationists currently have to rely on the general appearance of salmon as an indicator of their health, which is far from ideal. The new DNA chip will help farmers assess the state of their stock more accurately and also enable conservationists to sample wild populations to ascertain their health and well being. The development of the chip is the culmination of a four-year study known as Salmon To develop a more effective method of monitoring salmon health and performance the scientists have been studying salmon gene expression. By doing this, they have identified genes which play different roles in the lifecycle of salmon, for example immune response.