Locomotion of fish• Streamlined shape and mucoid

secretions that lubricate its body surface reduces friction between the water and the fish

• Water’s bouyancy properties also contribute to the efficiency of the fishes movement

• Fish move through the water using their fins and body wall to push against the incompressible water

Nutrition of fish and digestive system of fish

• Earliest fish were probably filter feeders

• Modern fish are predators and spend much of their lives searching for food

• Usually swallow their food whole

• Teeth capture and hold prey

• Gill rakers: trap plankton while the fish is swimming through the water with its mouth open

• Have a stomach that stores large and infrequent meals

• Small intestine is the primary site for enzyme secretion and food digestion

• Pyloric ceca-outpockets of the intestine increase absorptive and secretory surfaces

Fish digestive system

Circulation and gas exchange

Gas exchange• To maintain adequate levels

of oxygen the fish have to pass large quantities of water over their gills

• Ram ventilation: maintain water flow by holding their mouths open while swimming

• gas exchange across gill surfaces is very efficient

• Countercurrent exchange mechanism

Swim bladders and lungs• Pneumatic sacs: gas

chambers• Fish maintain vertical

buoyancy by their buoyant oils, the use of fins to provide lift, the reduction of heavy tissues and a swim bladder

• Control the amount of gas in the swim bladder to maintain buoyancy

Nervous system and sensory functions

• Central nervous system of a fish has a brain and spinal cord

• Sensory receptors are present throughout the body

• External nares: snout of fish for olfactory receptors

• Eyes: lidless and round• Receptors for equilibrium, balance

and hearing are in the inner ears• Lateral line system: used to detect

either water currents or a predator or a prey that may be causing water movements in the vicinity of the fish

Excretion and osmoregulation

• Osmoregulation is maintained by the kidneys and the gills

• Nephrons in the kidneys• Use osmotic uptake for

water across gill, oral and intestinal surfaces

• Excretion and defecation are constant

• Most excretion is ammonia

• cloaca-opening used for excretion, digestion and reproduction

Dog fish puffer

Parrot Fish

Mexican Walking Fish (amphibous fish)

Hand fish