Fishery products constitute an important part of international trade and the consumption of fish and seafood has increased. They are prime sources of animal protein also they have health advantages over red meats. As catches can often live in contaminated waters, with contamination coming from human and animal sources, fish can be involved in the transmission of pathogenic microorganisms and toxins.
But Unlike other animal products, quality and safety of fish is often more difficult to control due to variations in species, sex, age, habitats and action of autolytic enzymes as well as hydrolytic enzymes of microorganisms on the fish muscle.
Definition of fish:
The term fish is used to refer to any aquatic vertebrate that has a skin covered with scales, two sets of paired fins, some unpaired fins and a set of gills. They include hagfishes, lampreys, lobe-finned fishes, cartilaginous fishes and ray-finned fishes. Fish are the most diverse group of vertebrates alive today.
Structure of fish muscle:
The surface is adjacent to the skeleton. The blocks of muscle, which form the individual flakes in the cooked fish, are separated by thin sheets of what is known as connective tissue; these are curved within the fillet and run from the backbone to the skin. In fresh fish the muscle blocks are firmly attached to the connective tissue, and the surface of a cut fillet is smooth and continuous. There are also tiny blood vessels running through the muscle. The connective tissue accounts for only a small percentage of the total weight of the muscle, smaller than for example in beef muscle; this is one reason why fish is generally less tough to eat than meat Fish muscle is of two kinds, light muscle and dark muscle. In white fish there is a small strip of dark, or red, muscle just under the skin on both sides of the body, running beneath the lateral line. In fatty fish the strips of dark muscle are much larger in proportion and contain higher...