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