The liver in a fish serves digestion, waste removal and storage functions. The liver produces bile, which aids in the digestion of food as it processes through the stomach and intestines. This organ also serves as a food reserve, sustaining the fish when food resources are scarce.
Fish livers function analogously to the livers of many other animals, including humans. Bile is produced by the liver to break down fats and proteins, which allows the digestive system to extract more nutrients as food processes through the body. The liver is also used to remove waste from the blood and to aid in recycling old blood cells.
The livers of many fish species are rich in omega-3 fatty acids and vitamins A and D. Because of this characteristic, fish livers and fish liver extracts, especially from cod, are used in the production of nutritional supplements that are routinely consumed by humans.
The livers of sharks, skates and rays serve the added function of providing a means of remaining neutrally buoyant in the ocean. Shark livers contain high levels of a chemical called squalene, which serves as a substitute for a swim or air bladder that is found in species of bony fish.