Are gills part of digestion system in fish?

Gills are not part of the digestion system in fish. Their primary function is for respiration, enabling the exchange of oxygen and carbon dioxide between the water and the bloodstream. Gills extract dissolved oxygen from the water passing over them, which then enters the bloodstream and is transported to the body's tissues.

In contrast, the primary function of the digestion system is to break down food, absorb nutrients, and eliminate waste products. In most fish species, the major components of the digestion system include the mouth, esophagus, stomach, intestine, and digestive glands like the liver and pancreas. Through these structures and physiological processes, fish can consume food, break it down into usable nutrients, absorb these nutrients for energy and growth, and expel undigested materials as waste.

Therefore, gills serve a respiratory function, facilitating the uptake of oxygen, while the digestion system is responsible for processing food and obtaining essential nutrients.