any polyunsaturated fatty acid having a double bond between the sixth and seventh carbon atoms from the end of the molecule farthest from the carboxylic acid; although they are essential fatty acids, there is evidence that excess levels can cause a number of diseases
any polyunsaturated fatty acid having a double bond between the third and fourth carbon atoms from the end of the molecule farthest from the carboxylic acid; they are found in green vegetables and in the oils of fish such as salmon and mackerel; they are essential fatty acids, and seem to be beneficial in reducing the risk of heart disease
Both types of fish are available in cans, but unlike tuna, salmon is loaded with fat — healthy omega-3 fatty acids.