Fish

Actinopterygii

Approximately 40,000 (about 1/2 of all vertebrate species)

Homocercal

Usually Ctenoid (D-shaped, rougher surface) or Cycloid (round/smoother) Can also be ganoid, cosmoid, or scutes

Saltwater: drinks seawater, salts excreted through gills and gut. Produce small volume of relatively salty urine. Water loss by osmosis through gills and skin. Freshwater: does not drink, salts absorbed by gills, no salts enter gut. Produce large volume of dilute urine. Water gain by osmosis through gills and skin.

Sharks: gills block loss of urea, ingests salts with foods. Most urea retained by kidneys, salts excreted in urine & by rectal gland. Slight water gain by osmosis through gills and skin. Bony fishes (marine): gains water and salts by swallowing seawater and food. Salts excreted by chloride cells of gills, some salts pass through gut, some salts & water lost via urine. Kidneys retain water. Water loss by osmosis through gills and skin.

2 dorsal fins, caudal fin, anal fin

Pectoral fins and pelvic fins

1st dorsal fin. Primarily for maneuvering, stabilization & defense.

2nd dorsal fin. Primarily for low speed maneuvering and swimming.

Tail fin. Used for propulsion.

On ventral (bottom) side, toward back, opposite of soft dorsal. Used for stabilization.

Located on sides of body. Used for swimming, maneuvering, and stabilization.

On ventral side underneath the pectoral fins, used for stabilization.

Gill cover, bony and tough structure Protects gills and serves as “bellows” to help pump water over gills

Seals operculum and prevents back flow of water into the gill chamber

external nostrils, used in odor detection (not breathing)

Series of small fluid-filled canals lying just beneath the skin on the head and along the sides of the body (dark colored). System of receptors transforms underwater sound or mechanical disturbance into nerve impulses.

located just before the caudal fin Function: generates power to the caudal fin for swimming

located in middle of body cavity, comes after esophagus and before intestines function: food storage and digestion

finger-like structure located above/underneath the stomach function: aid in digestion and absorption

small, located toward front of body (between stomach/liver) sac, typically green, that holds bile for enzymatic digestion

located after stomach, large, twisty simple intestines, used for digestion

a diffuse organ, extending over the surface of the intestine and connective tissues/blood vessels. Can only be differentiated by using a microscope. function: secretion of digestive juices and insulin