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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