Are all the things which you have learned to consider when cooking meat and poultry little help when cooking fish? Yes! The muscle structure of mammals or birds is made up of very long fibres arranged in bundles held together by relatively thick connective tissue. When we cook mammals and birds the primary function of cooking is to tenderise the meat.
The muscle structure of fish is made up of rows of rather short fibres, separated by large sheets of very thin connective tissue. There is very little connective tissue in fish (about 3% by weight, compared to 15% in land animals)- and the connective tissue in fish is very fragile.
The combination of sparse, weak connective tissue and short muscle bundles in fish shifts the focus from tenderising, (as with land animals), to one of simply firming up the muscle fibres and melting away the thin connective tissue. The fish is then at it’s most tender, moist, and flavorful. Cooking beyond the point of doneness will only dry out and toughen the flesh.