Physiology of Finfish and Shellfish (2+1)

4.3.2 Metabolism

Nutrients consumed by fish are digested in the gut are absorbed by the gut lining and appear in the blood stream as their component molecules.

These molecules circulate in the body and are taken up by a variety of tissues, where they are subjected to a number of different chemical reactions. Metabolism refers to the physical and chemical processes that occur inside the cells of the body and they are necessary for the maintenance of life. In metabolism some substances are broken down to yield energy for vital processes while other substances are synthesized necessary for life. The transformation of the macro nutrients carbohydrates , fats and proteins in food to energy and other physiological processes are parts of the metabolic process. ATP (adinosene triphosphate) is the major form of energy used for cellular metabolism.

(Digestion is the process of dissolving food and breaking it down into simple chemical compounds in a living body while metabolism is the process of building up the chemical changes in living cells by which energy is provided and as similated into the system).

Through digestion proteins are broken down into amino acids, carbohydrates to simple sugars, and fats to glycerol and free fattyacids (FFA) . On absorption these smaller components end up in the liver, although fats take a circuitous route through tissue fluids and part of the lymphatic system known as the lacteals.

A number of metabolic processes occur in the liver. Amino acids are removed from the blood and stored temporarily prior to transport through the body for the synthesis of new fish proteins. There is a continual breakdown and synthesis of proteins which are used in cell and tissue structures, and enzymes. Any excess will be used for maintenance/movement energy, as it is broken down to carbon dioxide, water and ammonia . Absorbed sugars (from dietary carbohydrates) are converted to glucose in the liver which can then either be burned to supply energy or recombined to form glycogen which is stored in the liver as an energy reserve. The processes involved in the synthesis of proteins, fats and carbohydrates will be discussed later.