Define Fish as a rich source of protein?

The edible portion is skeletal muscles of the body. Even though the skeletal muscles of different animals are basically similar, fish species used for food are far more numerous and diverse than the mammalian species. Fish usually contains 40-60% edible flesh. Protein content of fresh water fish ranges from 13-25%. In the mid or lateral line of many fishes, there exists a layer of heavily pigmented reddish brown muscle that may contribute to 10% of total body muscle. This contains a high content of hemoprotein, which following the harvest, may catalyze oxidation of lipids and cause pronounced rancidity. The proteins may be classified as sarcoplasmic, myofibrillar or connective tissue protein.