Fishes

1
Fishes

• Chapter 24

2
Diversity

• Fish has many usages extending beyond what are
  actually considered fishes today (e.g., starfish,
  etc.).
• Fishes do not form a monophyletic group.
• In an evolutionary sense, can be defined as all
  vertebrates that are not tetrapods.
• Common ancestor of fishes is also an ancestor of
  land vertebrates.
• Therefore in pure cladistics, would make land
  vertebrates fish.
• Approximately 24,600 living species.
• Adapted to live in medium 800 times denser than
  air.
• Can adjust to the salt and water balance of their
  environment.

3
Diversity

• Evolution in an aquatic environment both shaped
  and constrained its evolution.
• Fish refers to one or more individuals of one
  species.
• Fishes refers to more than one species.

4
Ancestry of Fishes

• Fishes have descended from an unknown
  free-swimming protochordate ancestor.
• Agnathans including ostracoderms.
• Gnathostomes derived from one group of
  ostracoderms.
• Four groups of gnathostomes flourished during the
  Devonian, two survive today.

5
(No Transcript)
6
Fossils of Early Vertebrates

• Armored, jawless vertebrates called ostracoderms
  had defensive plates of bone on their skin.
• One group of ostracoderms led to the
  gnathostomes.

7
Fossils of Early Vertebrates

• Placoderms, one group of early jawed fishes, died
  out during the Carboniferous.
• Left no descendents.

8
Fossils of Early Vertebrates

• Another group, the acanthodians, were common
  during the Devonian, but became extinct during
  the Permian.
• They were distinguished by having heavy spines on
  all fins except the caudal (tail) fin.
• Possible sister group of the bony fishes.

9
Fossils of Early Vertebrates

• A third group of gnathostomes, the cartilaginous
  fishes (Class Chondrichthyes) lost the dermal
  armor and uses cartilage rather than bone for the
  skeleton.
• Sharks, skates, rays, chimaeras.

10
Fossils of Early Vertebrates

• The last group, the bony fishes, are the dominant
  fishes today.
• Ray-finned fishes include most modern bony
  fishes.
• Lobe-finned fishes contain few living species.
• Includes sister group of tetrapods.
• Lung fishes coelacanths.

11
Origins of Bone and Teeth

• Mineralization appears to have originated with
  vertebrate mouthparts.
• The vertebrate endoskeleton became fully
  mineralized much later.

12
Agnathans

• The least derived vertebrate lineages that still
  survives are class Myxini, the hagfishes and
  class Petromyzontida, the lampreys.
• They lack jaws, internal ossification, scales,
  and paired fins.
• Pore-like gill openings along the side of the
  body.

13
Class Myxini - Hagfish

• Entirely marine.
• Feeds on annelids, molluscs, crustaceans, dead
  or dying fishes.
• Predators or scavengers.

14
Class Myxini - Hagfish

• Hagfishes are jawless marine vertebrates that
  have a cartilaginous skull and axial rod of
  cartilage derived from the notochord.
• They lack vertebrae.

15
Class Myxini - Hagfish

• A hagfish can tie itself in knots to increase
  leverage when burrowing into a dead fish.
• Produces large amounts of slime.

16
Class Petromyzontida - Lampreys

• Lampreys (Class Petromyzontida) are found in
  fresh and saltwater.
• Lampreys have cartilaginous segments surrounding
  the notochord and arching partly over the nerve
  cord.

17
Class Petromyzontida - Lampreys

• All ascend freshwater streams to breed.
• Marine forms are anadromous.
• Freshwater forms move between lakes streams.

18
Class Petromyzontida - Lampreys

• Lamprey larvae are called ammocoetes.
• Larvae look much like amphioxus.
• Possess basic chordate characteristics in
  simplified form.
• Suspension feeders.

19
Class Petromyzontida - Lampreys

• Many are parasitic as adults.
• Those that are not, do not feed as adults.

20
Derived Characters of Gnathostomes

• Gnathostomes have jaws that evolved from skeletal
  supports of the pharyngeal slits.

21
Derived Characters of Gnathostomes

• Other characters common to gnathostomes include
• Enhanced sensory systems, including the lateral
  line system.
• An extensively mineralized endoskeleton.
• Paired appendages.

22
Fossil Gnathostomes

• The earliest gnathostomes in the fossil record
  are an extinct lineage of armored vertebrates
  called placoderms.

23
Fossil Gnathostomes

• Another group of jawed vertebrates called
  acanthodians radiated during the Devonian period.
• Closely related to the ancestors of osteichthyans
  (bony fishes).

24
Class Chondrichthyes

• Members of class Chondrichthyes have a skeleton
  that is composed primarily of cartilage.
• The cartilaginous skeleton evolved secondarily
  from an ancestral mineralized skeleton.

25
Subclass Elasmobranchii

• The largest and most diverse subclass of
  Chondrichthyes, Elasmobranchii, includes the
  sharks and rays.

26
Subclass Elasmobranchii

• Most sharks have a streamlined body and are swift
  swimmers.
• Heterocercal tail the upper lobe of the tail is
  longer than the lower.
• Placoid scales.
• The upper lower jaws have a front, functional
  row of teeth and several developing rows growing
  behind as replacements.

27
Subclass Elasmobranchii

• Spiral valve in intestine slows passage of food
  and increases absorptive area.
• Large fatty liver aids in buoyancy.

28
Subclass Elasmobranchii Acute Senses

• Prey is initially detected using large olfactory
  organs.
• Mechanorecptors in the lateral line system sense
  low-frequency vibrations from far away.
• Vision is important at close range.
• Bioelectric fields surrounding their prey can be
  detected using electroreceptors in the ampullae
  of Lorenzini on the sharks head.

29
Subclass Elasmobranchii

• All chondrichthyans have internal fertilization.
• Oviparous species lay large yolky eggs soon after
  fertilization.
• Some lay eggs in a capsule called a mermaids
  purse that often have tendrils to attach it to a
  some object.

30
Subclass Elasmobranchii

• Ovoviviparous species retain developing young in
  the uterus while they are being nourished by the
  yolk.

31
Subclass Elasmobranchii

• In viviparous species, young receive nourishment
  from the maternal bloodstream through a placenta,
  or from nutritional secretions produced by the
  mother.
• Some receive additional nutrition by eating eggs
  siblings.
• Parental care ends as soon as eggs are laid or
  young are born.

32
Subclass Elasmobranchii

• Skates and rays are specialized for bottom
  dwelling with a flattened body and enlarged
  pectoral fins.
• Gill openings on ventral surface.
• Water enters through spiracles on dorsal surface.

33
Subclass Elasmobranchii

• Stingrays have a slender whip-like tail with one
  or more saw-edged spines with venom glands at the
  base.
• Electric rays have large electric organs that can
  discharge high-amperage, low voltage current into
  the surrounding water.

34
Subclass Holocephali

• A second subclass is composed of a few dozen
  species of chimaeras, or ratfishes.
• Flat plates instead of teeth.
• Upper jaw fused to cranium.

35
Osteichthyes

• Osteichthyes are the bony fishes.
• Bone replaces the cartilage during development.
• A swim bladder is present for controlling
  buoyancy and respiration in some.
• Not a monophyletic group.

36
Osteichthyes

• Fishes breathe by drawing water over four or five
  pairs of gills located in chambers covered by a
  protective bony flap called the operculum.

37
Class Actinopterygii

• Ray-finned fishes (class Actinopterygii) contain
  all the familiar bony fishes more than 23,600
  species.

38
Class Actinopterygii

• The fins, supported mainly by long, flexible rays
  are modified for maneuvering, defense, and other
  functions.

39
Class Actinopterygii

• Two main groups of ray-finned fishes.
• Chondrosteans (e.g. sturgeons) have heterocercal
  tails and ganoid scales.

40
Class Actinopterygii

• Neopterygians one lineage of early
  neopterygians led to the modern bony fishes
  (teleosts).
• Early type neopterygians include the bowfin and
  gars.

41
Class Actinopterygii

• The major lineage of neopterygians are teleosts,
  the modern bony fishes.
• Changes in fins increased maneuverability and
  speed.
• Symmetrical, homocercal, tail allows increased
  speed.

42
Teleosts

• Thinner, lighter cycloid and ctenoid scales
  replace the heavy dermal armor of primitive
  ray-finned fishes. Some (e.g. eels) lack scales.

43
Teleosts

• Fins diversified for a variety of functions
  camouflage, communication, complex movements,
  streamlining, etc.

44
Teleosts

• The swim bladder shifted purpose from primarily
  respiratory to buoyancy.
• Gill arches in many diversified into pharyngeal
  jaws for chewing, grinding, and crushing.

45
Class Sarcopterygii

• Lobed-finned fishes (class Sarcopterygii) include
  2 species of coelacanths and 6 species of
  lungfishes.
• This group was much more abundant during the
  Devonian.
• Rhipidistians are an extinct group of
  sarcopterygians that led to tetrapods.

46
Class Sarcopterygii

• All early sarcopterygians had lungs as well as
  gills and a heterocercal tail.
• Later sarcopterygians have a continuous flexible
  fin around the tail.
• They have fleshy, paired lobed fins that may have
  been used like legs to scuttle along the bottom.

47
Class Sarcopterygii

• Some lungfishes can live out of the water for
  long periods of time.
• During long dry seasons, the African lungfish can
  burrow down into the mud and secrete lots of
  slime forming a hard cocoon where they will
  estivate until the rains return.

48
Class Sarcopterygii

• Coelocanths arose during the Devonian and peaked
  (max. species) in the Mesozoic.
• One genus, two species currently.
• Believed to be extinct for 70 million years,
  rediscovered in 1938.
• The second species was discovered in 1998.

49
Locomotion in Water

• Fishes use trunk and tail musculature to propel
  them through the water.
• Musculature is composed of zigzag bands called
  myomeres.

50
Locomotion in Water

• Flexible fishes like eels use a serpentine
  movement.
• Not very efficient for high speed.
• Fast swimmers are less flexible.
• Body undulations limited to caudal region.

51
Locomotion in Water

• Many fast swimmers are streamlined with grooves
  so their fins can lie flat.

52
Buoyancy

• Sharks must move constantly to avoid sinking.
• The heterocercal tail provides lift as it moves
  from side to side.
• Broad head and angled, stiff fins add lift.
• Their large livers with fatty hydrocarbons aid in
  buoyancy as well.
• Liver is like a large sack of buoyant oil.

53
Buoyancy

• Bony fishes use a gas-filled space to regulate
  buoyancy the swim bladder.
• Derived from a pair of lungs.
• Swim bladders are absent in tunas, abyssal
  fishes, many bottom dwellers.
• Bony fishes will sink without the swim bladder
  because they are denser than water.

54
Buoyancy

• Fishes must be able to regulate gas inside the
  swim bladder.
• At depth, the gas will compress and the fish will
  sink.
• As it rises to the surface, the gas will expand
  and the fish will rise faster.
• Gas may be removed in two ways.

55
Buoyancy

• Physostomous fishes (more primitive, e.g. trout)
  have a pneumatic duct that connects the swim
  bladder and the esophagus.
• Air can be expelled through the duct.
• Gas must be secreted into the swim bladder from
  the blood, although some species can gulp air to
  fill the swim bladder.

56
Buoyancy

• Physoclistous fishes (more derived, e.g. advanced
  teleosts) the pneumatic duct has been lost. Gas
  must be absorbed by blood from the highly
  vascularized ovale.
• Gas is secreted into the swim bladder from the
  blood at the gas gland.

57
Hearing

• The bodies of fishes are nearly the same density
  as water.
• Makes hearing difficult.
• Weberian ossicles, found in minnows, suckers,
  catfish, improves hearing.
• Sound detection starts in swim bladder (sound
  vibrates easily in air) and is transmitted to the
  inner ear by Weberian ossicles.

58
Respiration

• Fish gills are composed of thin filaments covered
  with an epidermal membrane that is folded into
  lamellae.
• Richly supplied with blood vessels.
• Located inside the pharyngeal cavity.
• Covered with an operculum in bony fishes.
• Elasmobranchs have gill slits.

59
Respiration

• Water must be continuously pumped over the gills.
• A countercurrent system is found where the flow
  of water is opposite to the flow of blood.
• Deoxygenated blood encounters the freshest water
  with the highest oxygen content.

60
Osmotic Regulation

• Freshwater fishes (hyperosmotic regulators) must
  have a way to get rid of water that enters their
  bodies by diffusion through the gills.
• Water enters the body, salts are lost by
  diffusion.
• Water is pumped out by the opisthonephric kidney
  which can form very dilute urine.
• Salt absorbing cells in the gill actively move
  salt from the water into the blood.

61
(No Transcript)
62
Osmotic Regulation

• Saltwater fishes (hypoosmotic regulators) have a
  lower blood salt concentration than the seawater.
• Tend to lose water and gain salts.
• Marine teleosts drink seawater.
• Salts are carried by the blood to the gills where
  they are secreted out by salt-secretory cells.
• Other salts are voided with feces or excreted by
  the kidney.

63
Feeding Behavior

• Most fishes are carnivores and prey on everything
  from zooplankton to large vertebrates.
• Some deep-sea fishes can eat victims twice their
  size an adaptation to scarce food.
• Most fishes cant chew with their jaws (this
  would block water flow over the gills), many have
  pharyngeal teeth in their throats.
• Large-mouthed predators can suck prey in by
  suddenly opening their mouths.

64
Feeding Behavior

• Herbivorous fishes eat plants and micro-algae.
• Most common on coral reefs parrotfishes,
  damselfishes, surgeonfishes.
• And tropical freshwater habitats minnows,
  characins, catfishes.

65
Feeding Behavior

• Suspension feeders filter microorganisms from the
  water using gill rakers.
• Herring-like fishes are common menhaden,
  herring, anchovies etc.
• Many larval fishes.
• Basking sharks.
• Most are pelagic fishes that travel in large
  schools.

66
Feeding Behavior

• Other groups are scavengers that eat dead and
  dying animals,
• Detritivores that consume fine particulate
  organic matter,
• Parasites that consume parts of other live fishes.

67
Migration

• Freshwater eels are catadromous, they enter the
  ocean as adults, migrate to a spawning area where
  they spawn then die.
• Larvae make their way back to the streams only
  females enter the streams.

68
Migration

• Anadromous salmon spend their lives at sea,
  returning to freshwater to spawn.
• Die after spawning.
• Strong homing instinct brings them to their
  parent stream.
• Guided by odor of parent stream.

69
Reproduction

• Most fishes are dioecious with external
  fertilization and external development
  oviparity.
• Ovoviviparous species (guppies, mollies,
  surfperches) bear live young after development in
  the ovarian cavity of the female.

70
Reproduction

• Fertilized eggs may be pelagic and hatch into
  pelagic larvae.
• Large yolky benthic eggs are often attached to
  vegetation or deposited in nests, buried, or even
  carried in the mouth.
• Many benthic spawners guard their eggs.
• Usually the male.

71
Reproduction

• In some species, males defend nest sites and
  perform courtship rituals to entice females to
  lay their eggs in his nest. Sometimes, several
  females will lay eggs in a nest.
• The male will guard the eggs from predators and
  will also fan them with his fins to aerate them.

72
Growth

• Larvae may depend on the yolk sac until their
  mouths and digestive systems are fully developed.
• Larvae then forage for their own food.

73
Growth

• Larvae metamorphose into juveniles with body
  shape color patterns usually similar to the
  adults.
• Some species have different color patterns in
  juveniles.

French Angelfishes (Pomacanthus paru) juvenile
(left) and adult (right).
74
Growth

• Growth is temperature dependent.
• Fish grow faster in summer when the temperature
  is warm and food is plentiful.
• Growth may nearly cease during the winter.
• Annual rings in scales, otoliths, and other bony
  parts reflect seasonal growth.
• Fish continue to grow throughout life.
• Larger fishes produce more gametes.