Chapter 41: Fishes

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Chapter 41 Fishes
41-1 Introduction to Vertebrates
41-2 Jawless Fishes, Sharks, and Rays
41-3 Bony Fishes
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41-1 Introduction to Vertebrates
I. Characteristics of Vertebrates (evolved 550
m.y.a.)

• Possess VERTEBRAE (protect DORSAL nerve cord), a
  CRANIUM (skull), and ENDOSKELETON (bone or
  cartilage)

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(1) Vertebrate Column

• Spinal column or BACKBONE that protects spinal
  cord.

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(2) Cranium

• Skull encases and protects the BRAIN.

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(A) Classification ( 45,000 species vertebrates,
MOST are fishes)

• SEVEN classes occupying TERRESTRIAL and AQUATIC
  habitats.

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(1) Lampreys and Hagfishes ( 80 species)

• Elongated, eel-like cartilaginous bodies LACKING
  jaws, paired fins, and bone.

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(2) Sharks, Rays, and Skates ( 800 species)

• Predatory fishes have JAWS, PAIRED FINS,
  skeletons of CARTILAGE, and a unique type of
  SCALE (integument).

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(3) Bony Fishes ( 23,000 species)

• Jaws, BONY skeleton TWO bony fish lineages(1)
  RAY-Finned Fishes (most species), (2) LOBE-Finned
  Fishes.

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(4) Amphibians ( 4,500 species)

• Thin, MOIST skin permeable to GAS exchange LAY
  eggs IN WATER and pass through an aquatic LARVAL
  stage.

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(5) Reptiles (6,000 species)

• Dry, SCALY skin with leathery eggs laid ON LAND,
  protected against desiccation.

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(6) Birds ( 10,000 species)

• Adaptations from reptiles allowing FLIGHT
  include feathers, HOLLOW bones, and unique
  RESPIRATORY system.

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(7) Mammals ( 4,400 species)

• Presence of INSULATING hair or fur and OFFSPRING
  are nursed with MILK from mammary glands.

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II. Evolution ( Evolution from Acanthodians,
Chordates 550 m.y.a.)

• EARLIEST appeared shortly after 1st chordates
  early JAWLESS fishes had HEAVY, bony scales
  (i.e., Class Agnatha)

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(A) Origin of Jaws (evolved 440 m.y.a.,
out-competing jawless ancestors)

• Evolved from GILL ARCHES as an adaptation
  favoring IMPROVED methods of obtaining nutrition
  (i.e., improved PREDATION)

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(1) Gill Arches (1st pair evolved into JAWS)

• Skeletal elements SUPPORT pharynx and evolved
  into first JAWS.

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41-2 Jawless Fish, Sharks, and Rays
I. Life in the Water (adaptations)

• Streamlined, muscular tail, paired AND unpaired
  fins, MUCUS coating, air bladder, and vascular
  GILLS.

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Critical Thinking
(1) Many species of fishes that live deep in the
ocean, where there is little or no light, are
luminescent. What might be the advantages and
disadvantages of such an adaptation?
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(A) Homeostasis (freshwater VS. marine species of
fish, osmosis)

• KIDNEYS and GILLS filter blood, regulate ION
  concentrations (Na, K), and RELEASE wastes.

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Critical Thinking
(2) Saltwater fishes drink more water and produce
much less urine than freshwater fishes do. How
could you account for this difference?
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(B) Sensory Functions (vary by species)

• Detect VIBRATIONS, and developed senses of
  SMELL, sight, hearing, and ELECTRICAL currents.

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(1) Lateral Line System (detects VIBRATIONS in
the water)

• A row of SENSORY organs run length of body on
  EACH SIDE connected by NERVES to BRAIN.

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II. Class Agnatha ( 80 species)

• Jawless fish LACKING vertebrae ? freshwater AND
  marine habitats.

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(A) Hagfishes (LACK vertebrae, retain notochord
cold, marine waters)

• Burrow into body of a DEAD or DYING fish through
  gills, skin, or anus and EAT internal organs.
  (i.e., NON-parasitic)

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(B) Lampreys (all breed in freshwater, BUT may
inhabit marine waters)

• PARASITIC ? require HOST to draw BLOOD from an
  inflicted WOUND.

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Critical Thinking
(3) When sea lampreys invaded the Great Lakes,
they devastated populations of their hosts. In
lakes where sea lampreys have lived for a long
time, host populations have NOT declined. Using
what you understand about co-evolution, explain
why this disparity may exist.
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(1) External Fertilization

• NEST is dug out of gravel and EGGS are released
  (fertilized by sperm, hatching into LARVAE
  resembling lancelets, develop into ADULTS).

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II. Class Chondrichthyes ( 800 marine species)

• CARTILAGINOUS fishes sharks, skates, and rays
  with JAWS, skeletons, and paired FINS.

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(1) Cartilage

• A flexible, LIGHT-WEIGHT material made of cells
  surrounded by tough fibers of PROTEIN.

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(2) Placoid Scales (a.k.a., denticles)

• Small, tooth-like scales (sandpaper) ? REDUCES
  friction of water during swimming. (BUT limits
  diffusion through skin)

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Critical Thinking
(4) Sharks have a large corkscrew-shaped
structure in the intestine called a spiral
valve. How do you suppose this organ might
function in digestion?
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(A) Sharks (use smell, lateral lines, vision, and
electrical fields to hunt)

• Predatory (tiger shark, bull shark) or
  filter-feeders (whale shark, basking shark) with
  senses (LARGEST brains of all fish) and
  REPLACEABLE teeth.

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Critical Thinking
(5) In a famous set of experiments, A. J. Kalmijn
studied the ability of sharks to find prey. He
showed that a shark could locate and capture a
stationary fish buried in the sand at the bottom
of a tank. When the fish was enclosed in
electrical insulation and then buried, however,
the shark could not locate it. From this
information alone, can you conclude that the
shark is using only its electrical sense to
locate the buried fish? Explain your answer.
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(1) Pectoral Fins (increased stability AND
maneuverability of fish)

• PAIRED fins behind head on VENTRAL side used for
  BALANCING.

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(2) Olfactory Bulbs (pick up SCENTs)

• Connect brain to nerve cells within NOSTRILS on
  snout ? monitor CHEMICALS in water, especially
  URINE and BLOOD.

                                                                                                         
TOP BOTTOM

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(B) Rays and Skates (BOTTOM dwellers feed on
mollusks and crustaceans)

• Flattened bodies with paired WING-like PECTORAL
  fins, and in some cases, WHIP-like tails.

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(C) Adaptations of Cartilaginous Fishes

• Gills and spiracles CONVERT ammonia to urea
  (less toxic, storable, no need to drink as OAS
  levels are matchedbody ocean)
• Breathe by SWIMMING (spiracles) OR just by
  EXPANDING and CONTRACTING their mouth cavity
  (gills).

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(1) Rectal Gland

• Removes EXCESS ions from blood and RELEASES them
  into rectum.

NOTE BUOYANCY is maintained via SWIMMING
(generates upward LIFT) and low-density LIPID
storage in the LIVER (oil FLOATS in water),
REDUCING body density (an NRG saver).
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(D) Reproduction of Cartilaginous Fishes

• DIFFER from jawless fish in that fertilization
  is INTERNAL in female. (NOTE Yolky egg can be
  LAID or RETAINEDlive birth)

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(1) Internal Fertilization

• Females lay large, yolky eggs after
  fertilization young develop within egg
  (nourished by yolk) AND hatch as juveniles. (NO
  parental care given)

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(2) Claspers (ONLY found in MALES)

• During MATING, male transfers sperm INTO
  females body with MODIFIED PELVIC fins and may
  BITE the fin to HOLD ON.

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41-3 Bony Fishes
I. Characteristics of Bony Fishes ( 24,000
species, 2 groups)

• Inhabit freshwater AND marine habitats 3 key
  features.

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Critical Thinking
(6) Cod and many other ocean fishes lay eggs near
the surface of the water. The male largemouth
bass scoops out a nest in a lake or river bottom
and waits for a female to deposit her eggs. What
hypothesis would you make regarding the relative
number of cod and bass eggs? Explain your answer.
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(1) Bone (calcified)

• Harder AND heavier than cartilage ENDOSKELETON.

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(2) Lungs (early bony fishes) or Swim Bladder
(gas filled sac)

• Gas exchange in a few LUNG fishes MOST use
  bladder for BUOYANCY (i.e., modified lung)

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Critical Thinking
(7) Bottom-dwelling fish often lack a swim
bladder. Explain the adaptive advantage of this
adaptation.
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(3) Scales

• Protect AND reduce water FRICTION while swimming.

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(A) Lobe-Finned Fishes ( 6 species of lungfish,
1 species of coelacanth)

• Fleshy fins supported by bone (NOTE
  Lobe-finned fishes are believed to be ANCESTORS
  of amphibians and all other terrestrial
  vertebrates).

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(B) Ray-Finned Fishes ( MAJORITY of bony fishes)

• Fins supported by long, flexible BONY rays
  (Fins do NOT have a central bony
  axis)

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II. External Anatomy

• Yellow PERCH is bony fish head, trunk and
  tail regions.

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(1) Operculum (located on EACH side of the head)

• Hard COVERING opens at rear and PROTECTS gills.

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(A) Fins (FOUR types)

• For swimming (propulsion, steering, and balance).

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(1) Caudal Fin (tail fin)

• Moves from side to side ? PROPELS the body.

(2) Dorsal Fins (back fins)

• Keeps fish UPRIGHT and moving in a STRAIGHT line.

(3) Anal Fin

• Ventral fin works with dorsal fins for BALANCE.

(4) Pelvic Fins

• Paired with PECTORAL fins to steer, stop, move
  up/down, and back up.

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(B) Skin (covered with scales)

• Thin, round disks of a bone-like material grow
  from pockets in skin.

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III. Internal Anatomy

• Protected by skeletonskull, spinal column
  (vertebrae with cartilage pads), pectoral girdle,
  pelvic girdle, and ribs.

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(1) Pectoral and Pelvic Girdles (fin support)

• Attachment points for FINS in to skeleton.

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(A) Digestive System

• Jaws are designed to GRIP and TEAR prey.

(1) Esophagus

• CONNECTS mouth to stomach.

(2) Stomach

• Secretes acid AND digestive enzymes.

(3) Intestine

• Nutrients ABSORBED into bloodstream.

(4) Liver

• Makes and secretes BILE into gall bladder.

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(5) Gall Bladder

• Stores AND releases BILE into intestine for
  lipid digestion (emulsifies fats).

(6) Pancreas

• Makes AND releases digestive enzymes into
  intestine.

(7) Anus

• Eliminates undigested food material FROM
  intestines.

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(B) Circulatory System

• Carries O2, CO2, nutrients, NH4 throughout body
  (e.g., consists of
  4-pseudo-chambered heart)

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(1) Arteries (AWAY from heart)

• Carry blood pumped FROM heart to capillaries.

(2) Capillaries (SITES of exchange)

• Thin-walled TINY vessels where GAS EXCHANGE
  occurs.

(3) Veins (TOWARD the heart)

• Returns blood from the body back TO heart.

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(4) Sinus Venosus (Pseudo-Chamber 1)

• Receives d-Blood from body.

(5) Atrium (Chamber 2TRUE CHAMBER)

• FORCES blood into muscular VENTRICLE, main
  pumping chamber.

(6) Ventricle (Chamber 3TRUE CHAMBER)

• FORCES blood THROUGH GILLS and BODY with GREAT
  pressure.

(7) Conus Arteriosus (Pseudo-Chamber 4)

• Uses valves to PREVENT blood from flowing
  BACKWARD into ventricle (smoothes flow of
  blood from heart).

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(C) Respiratory (gills AND gill rakers) and
Excretory System

• Water pulled into mouth AND pumped OVER gills,
  before EXITING behind operculum.

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(1) Countercurrent Flow (water flows away from
head, blood toward head)

• Blood in capillaries AND water flow in OPPOSITE
  directions (i.e.,
  This optimizes the diffusion of oxygen INTO the
  blood)

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(2) Urine (made from kidneys filtering blood)

• CONTAINS NH4, ions, and water.

(3) Urinary Bladder

• Stores urine UNTIL it is excreted.

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(D) Swim Bladder

• GAS in this thin-walled abdominal SAC, enabling
  RISING or SINKING.

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(E) Nervous System

• Brain, spinal cord, peripheral nerves connecting
  to SENSORY organs.

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(1) Cranial Nerves

• Connect SENSORY organs with brain through
  FORAMEN in the skull.

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(2) Cerebrum (part of the FOREBRAIN)

• Integrates sensory data from OTHER parts of
  brain.

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(3) Optic Tectum (dominates midbrain)

• Receives processes infovisual, auditory, and
  lateral line systems.

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(4) Cerebellum (part of the HINDBRAIN)

• Helps to coordinate fishs motor output
  (locomotion AND balance)

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(5) Medulla Oblongata

• Regulates body functions AND relay station for
  senses.

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(6) Spinal Nerves

• Connect SPINAL CORD with organs, muscles, and
  senses.

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(F) Reproduction (an egg-layer is described as
being OVIPAROUS)

• Majority EXTERNAL fertilization with eggs laid
  OUTSIDE body.

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(1) Spawning (with EXTERNAL fertilization)

• Reproductive EGG-LAYING behavior influenced by
  NESTING sites.

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Extra Slides AND Answers for Critical Thinking
Questions
(1) Fishes that have lived a long time with
lampreys have evolved ways to protect themselves.
The Great Lakes fishes had not yet done so.
(2) The spiral valve probably increases the
surface area available for the absorption of
nutrients.
(3) The experiment does not exclude the
possibility that sharks are finding their prey by
smell. Although the insulating material would
block electrical signals from the prey fish, it
might also block the fishs odor. (In fact,
Kalmijn conducted further experiments to
demonstrate that sharks could detect the fish by
its electrical discharges only.
(4) The body fluids of a freshwater fish have a
higher concentration of ions than does fresh
water. Thus, freshwater fishes gain water and
rid themselves of this water by producing large
amounts of urine. They do not need to drink.
Saltwater fishes, by contrast, have lower ionic
concentrations than sea water, so they lose
water. They must drink to replace this water,
and they conserve water by producing little urine.
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(5) Because swim bladders help fishes float, a
bottom dweller would be disadvantaged if it did
float.
(6) It probably attracts desirable prey.
(7) It is likely that the bass would produce
fewer eggs for two reasons. First, because it
provides some protection for its eggs, their
mortality likely will be lower. Fewer eggs will
be lost and need to be replaced. Second, because
the bass invests more in each egg, it does not
have the resources to produce as many eggs.
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