The main structural similarities between fish and meat are in the form of the muscle fibres. The major structures of the two are quite different, however. Unlike meat, fish flesh is composed of muscle sheets running head to tail on each side of body, divided into segments by perpendicular sheets of connective tissue.
Cooked fish has a tender, delicate texture for two reasons. Firstly, fish flesh contains much less connective tissue than is found in warm-blooded animals, and secondly, contains more thermally unstable collagen, which liquefies on heating. This causes the structure to fall apart when force is applied, as the bonds caused by connective tissue are no longer present. Connective tissue properties influence the texture of raw fish, whereas cooked fish is influenced by muscle fibre properties.
