Most fish are predators, actively hunting. Others are filter feeders that can use the the gill rakers off of the gill arches to direct food inward. 1 Fish have a stomach for storage of large, infrequent meals. The intestine has outpocketings or pyloric ceca in some bony fish. Pancreas, liver, and gallbladder are additional digestive organs.
Most fish pump water over the gills with pharyngeal and opercular muscles.
There are separate oral and opercular cavities. Gill arches support gill filaments which are covered by gill lamellae. Blood in the capillaries and water rushing over the gills flow in the opposite direction, or countercurrent mechanism . This allows the maximal extraction of oxygen possible out of the water. Lungs are endodermal derivations from the posterior pharynx, and so are homologous to the swim bladder.