Fishes

• The most abundant and diverse of all vertebrate groups
• The oldest known first true vertebrates appeared in the fossil record 530 MY ago (early Cambrian)

  
• Probably sucked up small particles of food from the bottom sediments
• They eventually developed primitive fins that improved their swimming ability
• Fish occupy virtually every kind of freshwater and saltwater habitat
• There are no terrestrial fish
• Smallest fish


  Males 7 mm long, females 8.4 mm and weighs 1 mg
• Largest fish


  50 to 70 feet (40 tonnes)
• Most fish continue to grow (temperature dependent) throughout life
• Annual rings are produced in scales, otoliths, and other bony parts
• Epidermis


  Usually secretes slimy mucous to reduce friction
• Dermis


  Sometimes tough and leathery or relatively thin, produces scales in most fish
• Scales


  Made of enamel and sometimes dentin, the same basic components as our teeth
• Skeleton begins as a cartilage framework in most fish and is replaced by bone by adulthood

  
• Bone is a tissue unique to the vertebrates
• Fish have ribs but they are not used for "breathing" but support swimming muscles
• Most fish have paired appendages in the form of pectoral and pelvic fins (appendicular skeleton)

  
• Fins


  • Act as rudders, for balance, feelers, weapons, sucking discs lures to attract prey
• Body mass


  Bundles of segmented muscle tissue / myomeres / myotomes, mainly for swimming although some can walk, crawl, burrow, and "fly"
• Less energy is required for swimming than most other forms of vertebrate locomotion
• Each myomere consists of short muscle fibers connected to the tough connective tissue that is also attached to the next myomere
• Myomeres produce "S" shaped swimming motion
• Swimming speeds are not particularly fast compared to running or flight due to the high density of water
• The larger the fish the faster it can usually swim
• Flying fish can glide above the water for 20-40 sec
• Dorsal and ventral fins improve swimming efficiency
• Teeth


  Small, numerous, sharp teeth are used to seize prey
• Most fish have very flexible jaws to engulf large prey
• Most fish lack moveable tongues
• Fish swallow their food whole; they don't "chew"
• Opercular and pharyngeal muscles

  Pump water in most fishes
• Ram ventilation


  In elasmobranchs and open-ocean bony fish
• Gill (visceral) arches support gills
• Gill filaments and pharyngeal lamellae
• Circulatory system


  Blood flows through a single circuit: heart →arteries → capillaries →veins → back to the heart
• Fish are cold-blooded; ie poikilotherms
• The body temperature of most fish is the same as their environment
• High temperatures promote swimming and improved nervous activities
• Brain


  Made up of several distinct functional areas: cerebrum (higher centers) very small, cerebellum (coordination of movement) relatively large, brain stem (automatic activities) also relatively large
• Fish do sleep, stay motionless for several hours