Abnormalities in fish muscle represent not only an ethical and welfare issue, but may also have a negative impact on economy and market acceptance due to growth impairment in affected fish, elevated mortality and reduced fillet quality. Alertness and know ledge on this field is also important for the reputation of the aquaculture industry as the public will have an even lower acceptance for abnormalities in the food, than for skeletal and internal organ malformations in intensive animal production. Little information exists on muscle abnormalities, only a few reports describing some muscle pathological observations like obliteration of striation, fibre loss and irregular fibres. However, all three partners in this project have observed muscle abnormalities on several occasions working with harvest sized fish. It is not known if alterations in muscle structure are caused by environmental or genetic factors, if abnormal muscle can be linked to meat quality problems or to other kinds of deformities observed i n both wild and farmed fish. As observations of abnormalities in the muscle are quite frequent and no studies have been done in this field, it is important for the aquaculture industry to gain knowledge on the extent of muscle abnormalities in farmed fish , and whether or not it represents a production problem and potential market risk for the industry. Thus, the principle objective of the project is to gain knowledge about muscle abnormalities in intensively farmed salmon populations in order to ensure no rmal muscle development and growth, good animal welfare and high product acceptability in aquaculture. In the project we will identify the types and extent of muscle abnormalities in intensively farmed salmon populations, study the causatives of muscle ab normalities and possible links to skeletal malformations and product quality problems and provide knowledge on mechanisms behind muscle abnormalities.