Fish internal structure and nervous system

The carp’s digestive tract: mouth cavity, pharynx, gullet and intestine; it has no teeth on its jaws (throat teeth grind the food) and no separate stomach, so food goes straight to the intestine (predatory fishes have toothed jaws and a stomach). In the small intestine pancreatic juice and bile from the liver digest food and absorbed substances enter the blood. Fishes breathe with gills: water taken in through the mouth leaves via the gill slits, oxygen passes into blood in the capillaries of the gill filaments and carbon dioxide into the water. Gill rakers keep food from escaping with the water. Circulation is a single circuit: the heart has two chambers (atrium and ventricle); blood goes from the ventral aorta to the gills, enriched with oxygen to the dorsal aorta and then to the organs; venous blood returns to the atrium. Excretion: two ribbon-like kidneys, ureters and a bladder. Fishes are cold-blooded: body temperature follows the surroundings. Under ice in winter or in hot summer water with low oxygen, fishes can die.