Chapter 5

• Osteichthyes


  The vast majority of fish, the most various group of vertebrates, consisting of over 29,000 species, the largest class of vertebrates
• Osteichthyes


  • Their skeleton is made of bone instead of cartilage
  • Most species produce eggs rather than bearing live young, with many spawning
• Types of Osteichthyes


  • Ray-finned fish (Actinopterygii)
  • Lobe finned fish (Sarcopterygii)

  
• Most bony fish belong to the Actinopterygii, there are only eight living species of the Sarcopterygii including the lungfish and coelacanth

  
• Osteichthians


  • Relatively stable pattern of cranial bones
  • Rooted teeth
  • Medial insertion of mandibular muscle in lower jaw
  • Head and pectoral girdles covered with large dermal bones
  • Eyeball supported by a sclerotic ring of four small bones
  • Labyrinth in the inner ear contains large otoliths
  • Braincase divided into anterior and posterior sections
  • Lung or swim bladder
  • No fin spines, instead support fin with lepidotrichia (bone fin rays)
  • Operculum to help breathe without having to swim
• Dermal scales


  Ganoid, cycloid, or ctenoid
• Spiracles


  Present in primitive groups
• Internal nares


  With or without
• Lung or swim bladder


  With or without duct
• Reproduction


  Mostly oviparous with external fertilization, some ovoviviparous or viviparous
• Fish are animals that are cold-blooded, have fins and a backbone. Most fish have scales and breathe with gills.
• Largemouth bass


  • Typical torpedo-like (fusiform) shape
  • Body consists of head, trunk, and tail
  • Fins used for maintaining position, movement, steering, and stopping
• Types of fins


  • Single fins along centerline (dorsal, caudal, anal)
  • Paired fins (pectoral, pelvic)
  • Adipose fin (in catfish)
• Caudal fin


  Main fin for propulsion, homocercal (two lobes equal)
• Skin and color


  • Tough, contains blood vessels, nerves, connective tissue, mucus-producing cells, and chromatophores (pigment cells)
  • Silvery pigments produce bright rainbow colors in sunlight
• Scales


  • Ctenoid (jagged edges) or cycloid (smooth rounded edges)
  • Growth rings called circuli and annuli allow age estimation
• Gills


  Highly vascularized breathing apparatus, protected by flexible bony operculum
• Fish vision


  Detects color, eyes rounder than mammals due to water's refractive index, focus achieved by moving lens
• Nostrils (nares)


  Used to detect odors, can be quite sensitive
• Mouth shape


  Indicates diet, larger mouths can consume bigger prey, some have teeth for seizing, tearing, or grinding food
• Vent


  External opening to digestive, urinary, and reproductive tracts
• Skeleton


  • Backbone with vertebrae, skull supports mouth and gills
• Muscles


  • Skeletal muscles for movement, smooth muscles for internal organs, heart muscles
• Digestive system


  • Mouth, pharynx, esophagus, stomach, intestines, anus
  • Some have gizzard or pyloric caeca to aid digestion
  • Liver assists digestion and other functions
• Swim/air bladder


  Hollow, gas-filled balance organ that allows fish to maintain neutral buoyancy
• Fish get oxygen from dissolved oxygen in water, gulping water over their gills
• Pyloric caeca


  • Fingerlike projections located near the junction of the stomach and the intestines
  • Their function is not entirely understood, but it is known to secrete enzymes that aid in digestion, may function to absorb digested food, or do both
• Liver


  • Assists in digestion by secreting enzymes that break down fats
  • Serves as a storage area for fats and carbohydrates
  • Important in the destruction of old blood cells and in maintaining proper blood chemistry
  • Plays a role in nitrogen (waste) excretion
• Swim or air-bladder


  A hollow, gas-filled balance organ that allows a fish to conserve energy by maintaining neutral buoyancy (suspending) in water
• Respiratory system of fish

  1. Water contains dissolved oxygen

  2. Fish gulp water through the mouth and pump it over the gills

  3. Water passes into the gill chambers and flows over the gills

  4. Gill filaments absorb oxygen from the water and replace it with carbon dioxide

  5. Water then passes out through the gill openings
• Circulatory system of fish

  • Heart consists of two main chambers - the atrium and the ventricle
  • Blood flows through veins to the atrium, then to the ventricle
  • Ventricle pumps the blood through arteries to the gills, where the blood receives oxygen and gives off carbon dioxide
  • Arteries then carry the blood throughout the body
  • Blood carries food from the intestines and oxygen from the gills to the body cells, and carries away waste products from the cells
  • Kidneys remove the waste products from the blood, which returns to the heart through the veins
• Nervous system of fish

  • Consists of a spinal cord, brain, and nerves
  • Not as complex as that of mammals and other higher vertebrates
  • Spinal cord runs from the brain through the backbone
• Sense organs of fish

  • Eyes are analogous to those of sharks, without eyelids and non-modifiable lens
  • Accommodation is done by the change in location of two specialized structures: the calciform ligament and the Haller organ
  • Lateral line is a sensory organ consisting of fluid filled sacs with hair-like sensory apparatus that are open to the water through a series of pores
  • Lateral line primarily senses water currents and pressure, and movement in the water
• Excretory system of fish

  • Opisthonephric kidneys are situated dorsally in the abdominal cavity
  • They filter liquid waste materials from the blood and pass them out of the body
  • Kidney is also extremely important in regulating water and salt concentrations within the fish's body, allowing certain fish species to exist in freshwater or saltwater
  • Vent is the site of waste elimination from the fish's body
• Reproductive system of fish

  • Testes in males and ovaries in females
  • In adult female bass, the bright orange mass of eggs is unmistakable during the spawning season
  • Male organs, which produce milt for fertilizing the eggs, are much smaller and white but found in the same general location
  • Eggs (or roe) of certain fish are considered a delicacy, as in the case of caviar from sturgeon
  • Most fish release their sex cells into the water through an opening near the anus
  • Males of some species have special structures for transferring sperm directly into the females
• Electric fish


  • Produce electricity from an organ in the tail called an 'electric organ'
  • Electric organ contains electrically excitable cells called 'electrocytes', which receive simultaneous command signals from the brain to 'fire'
  • Simultaneous firing of electrocytes results in the electric organ discharges (EODs) which are emitted in the surrounding water
  • Strongly electric fishes, such as the electric eel, electric catfish, and electric rays, have a huge electric organ containing numerous electrocytes, with discharge voltage reaching as high as 600 volts
  • Weakly electric fishes, which use electricity for navigation and communication, have a small discharge voltage, often less than a volt
  • Electroreceptors are used to detect a slight change of electric field caused by nearby objects, allowing electric fishes to 'electrically see' objects in an environment where vision is useless
• Bioluminescence


  • Living light generated by organisms through biochemical reactions
  • Often involves an enzyme, luciferase, which catalyses the light-emitting oxidation of a substrate, luciferin
  • Different luciferins and luciferase are found in different organisms, and the reaction does not always involve oxygen
  • Functions include lightening the environment, protection from predators and sexual communication in certain species
  • Luminescent fish include Myctophids, Anomalops, and deep water angler fish
• Types of fish migration

  • Holobiotic migrations (within salt water or within fresh water)
  • Potamodromous fish (migrate within fresh water only)
  • Oceanodromous fish (migrate within salt water only)
  • Amphibiotic migrations (between fresh and salt water, also called diadromous migration)
  • Anadromous fish (live in the sea mostly, but move to fresh water to breed)
  • Catadromous fish (live in fresh water, but migrate to the sea to breed)
  • Amphidromous fish (migrate between fresh and salt water during part of life cycle, but not for breeding)