Transcript Chapter 24

CHAPTER 24
Fishes
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Diversity
Overview
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“Fish” has many usages extending beyond
what are actually considered fishes today
(e.g., starfish, etc.)
A modern fish
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Fishes
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Aquatic vertebrate with gills, limbs (if present) in
the form of fins, and usually with a skin covered
in scales of dermal origin
In an evolutionary sense, can be defined as all
vertebrates that are not tetrapods
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Diversity
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Common ancestor of fishes is also an ancestor of
land vertebrates
Approximately 24,600 living species
 Include more species than all other vertebrates
combined
Adapted to live in medium 800 times denser than air
Can adjust to the salt and water balance of their
environment-osmotic balance
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Diversity
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Gills are efficient at extracting oxygen from
water that has 1/20 the oxygen of air
Lateral line system detects water currents
and vibrations, a sense of “distant touch”
and used in schooling
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
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Ancestry and Relationships of Major Groups of Fishes
History
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Earliest fish-like vertebrates: Group of
agnathan fishes
Agnathans “jawless”
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Include extinct ostracoderms and living hagfishes
and lampreys
 Hagfishes lack vertebrae
 Lampreys have rudimentary vertebrae
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Ancestry and Relationships of Major Groups of Fishes
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Gnathostomes “jawed”
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Appear in the Silurian fossil record with fully
formed jaws
No intermediate forms between agnathans are
known
The Devonian is called the Age of Fishes
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Ancestry and Relationships of Major Groups of Fishes
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Cartilaginous Fishes
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Lost heavy dermal armor and adopted skeleton of
cartilage
Flourished during the Devonian and
Carboniferous
Almost became extinct at end of the Paleozoic
Increased in numbers in the early Mesozoic,
diversifying to form a modern shark assemblage
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Ancestry and Relationships of Major Groups of Fishes
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Bony Fishes
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Dominant fishes today
Two distinct lineages
 Ray-finned fishes
 Lobe-finned fishes
Ray-finned fishes radiated to form modern bony
fishes
Lobe-finned fishes are a relict group with few
species today
 Include the sister group of the tetrapods
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Living Jawless Fishes
Overview
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Living jawless fishes include hagfishes and
lampreys
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Members of both groups lack jaws, internal
ossification, scales, or paired fins
Both groups share porelike gill openings and an
eel-like body
Hagfish
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Living Jawless Fishes
Hagfishes
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Entirely marine
Scavengers and predators of annelids,
molluscs, dead or dying fishes, etc.
Enters dead or dying animal through orifice
or by digging inside using keratinized plates
on tongue
Nearly blind
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To provide leverage
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Locate food by an acute sense of smell and touch
Ties knot in tail and passes it forward to press
against prey
Special glands along body secrete fluid that
becomes slimy in contact with seawater
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Living Jawless Fishes
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Reproduction of Hagfishes
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Copenhagen Academy of Science offered a prize
over a century ago for information on hagfish
breeding habits………it remains unclaimed
In some species, females outnumber males by
100 to 1
Females produce small numbers of large, yolky
eggs 2-7 centimeters in diameter
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Living Jawless Fishes
Lampreys
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Diversity
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Marine lamprey
 Occurs on both Atlantic coastlines
 Grows to a length of one meter
20 species of lampreys in North America
 Half belong to nonparasitic brook-dwelling
species
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Living Jawless Fishes
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Parasitic Lampreys
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Marine, parasitic lampreys migrate to the sea
Other species remain in freshwater
Attach to a fish by a sucker-like mouth
Sharp teeth rasp through flesh as they suck fluids
Inject anticoagulant into a wound
When engorged, lamprey drops off but wound may
be fatal to fish
Parasitic freshwater adults live 1–2 years before
spawning and dying
Anadromous forms live 2–3 years
Nonparasitic lampreys do not feed
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Digestive tract degenerates as an adult
They spawn and die
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Living Jawless Fishes
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Sea Lamprey Invasion of the Great Lakes
Region
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No lampreys were in the U. S. Great Lakes west of
Niagara Falls until the Welland Ship Canal was
deepened between 1913 and 1918
Lampreys preferred lake trout
Destroyed this commercial species along
with overfishing
 Lamprey populations declined both from
depletion of food and control measures
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Chemical larvicides in spawning streams
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Class Chondrichthyes: Cartilaginous Fishes
Overview
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Well-developed sense organs, powerful jaws,
and predaceous habits helped them survive
True bone is completely absent throughout
the class
Phosphatized mineral tissues retained in
teeth, scales, and spines
Nearly all are marine
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Only 28 species live primarily in freshwater
After whales, sharks are the largest living
vertebrates, reaching 12 meters in length
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Class Chondrichthyes: Cartilaginous Fishes
Sharks, Skates and Rays
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coastal tiger and bull sharks and the hammerhead
large, pelagic sharks such as the white and mako
shark
dogfish sharks
skates
several groups of rays (stingrays, manta rays, etc.)
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Class Chondrichthyes: Cartilaginous Fishes
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Form and Function of Sharks
Sharks are among the most gracefully
streamlined of fishes
In males, part of the pelvic fin is modified to form
a clasper used in copulation
Lateral eyes are lidless
Behind each eye is a spiracle
 Remnant of the first gill slit
Tough, leathery skin with placoid scales
 Reduce water turbulence
Detect prey at a distance by large olfactory
organs sensitive to one part per 10 billion
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Class Chondrichthyes: Cartilaginous Fishes
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Nostrils to each side of the hammerhead shark may
improve stereo-olfaction
Prey may also be located from long distances
sensing low frequency vibrations in the lateral line
 Consists of neuromasts in interconnected tubes
and pores on side of body
At close range, switch to vision
 Most have excellent vision even in dimly lit water
Up close, sharks are guided by bioelectric fields
that surround all animals
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Class Chondrichthyes: Cartilaginous Fishes
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Electroreceptors, the ampullae of Lorenzini, are
located on the shark’s head
Upper and lower jaws equipped with sharp,
triangular teeth (modified placoid scales) that are
constantly replaced
Spiral valve in intestine slows passage of food
and increases absorptive area
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Class Chondrichthyes: Cartilaginous Fishes
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Reproduction and Development
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Fertilization is internal
Maternal support of embryo is variable
 Includes oviparous, ovoviviparous, and
viviparous species
“Mermaid’s purse”
 capsule encasing eggs laid by some oviparous
species
 Sharks
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Class Chondrichthyes: Cartilaginous Fishes
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Rays & Skates
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Most specialized for benthic life
flattened body and enlarged pectoral fins used to
propel themselves
Respiratory water enters through large spiracles on
top of the head to prevent clogging of gills.
Teeth adapted for crushing prey
 Molluscs, crustaceans, and sometimes small fish
Stingrays
 Have whiplike tail with spines and venom glands
Electric rays
 Have large electric organs on each side of head
 Stingrays
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Class Chondrichthyes: Cartilaginous Fishes
Chimeras
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Small subclass
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Fossil chimaeras
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Remnants of a line that diverged from the earliest
shark lineage
33 extant species
First appeared in the Carboniferous, reached a
zenith in the Cretaceous and early Tertiary, and
then declined
Mouth lacks teeth
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Equipped with large flat plates for crushing food
Upper jaw fused to the cranium
Feed on seaweed, molluscs, echinoderms,
crustaceans, and fish
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Osteichthyes: Bony Fishes
Origin, Evolution and Diversity
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In early to middle Silurian, a lineage of fishes
with bony endoskeletons gave rise to a clade
that contains 96% of living fishes and all
living tetrapods
3 features unite bony fishes and tetrapod
descendants
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Endochondral bone replaces cartilage during
development
Lung or swim bladder is present
 Evolved as an extension of gut
Have several cranial and dental characters unique
to clade
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Osteichthyes: Bony Fishes
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2 major lineages
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Operculum increased respiratory efficiency
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Ray-finned fishes,modern bony fishes
Lobe-finned fishes, lungfishes and the coelacanth
Helped draw water across gills
Gas-filled structure off the esophagus
 Helped in buoyancy and also in hypoxic waters
 In fishes that use these pouches for respiration
 Pouches are called lungs
 In fishes that use these pouches for buoyancy
 Pouches are called swim bladders
Specialization of jaw musculature improved
feeding
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Ray-finned Fishes
Morphological Trends
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Heavy dermal armor replaced by light, thin,
flexible cycloid and ctenoid scales
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Fins changed to provide greater mobility and
serve a variety of functions
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Some eels, catfishes, and others lost scales
Increased mobility from shedding armor helps fish
avoid predators and improved feeding efficiency
Braking, streamlining, and social communication
Jaw changed to increase suctioning and
protrusion to secure food
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Class Sarcopterygii: Lobe-finned Fishes
Diversity
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Ancestor of tetrapods
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Early sarcopterygians
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Group of extinct sarcopterygian fishes called
rhipdistians
Had lungs, gills
Had powerful jaws, heavy, enameled scales with a
dentine-like material called cosmine, and strong,
fleshy, paired lobed fins
Today, clade is represented by 8 fish species
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6 species of lungfishes and 2 species of coelacanths
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Class Sarcopterygii: Lobe-finned Fishes
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Lungfish
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Australia lungfishes, unlike close relatives, rely
on gill respiration and cannot survive long out of
water
South American and African lungfish can live out
of water for long periods of time
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Class Sarcopterygii: Lobe-finned Fishes
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The Coelacanth
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Thought to be extinct 70 million years, a specimen
was dredged up in 1938
More were caught off coast of the Comoro Islands
and in Indonesia
Young coelacanths born fully formed after
hatching from eggs up to 9 cm in diameter
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Structural and Functional Adaptations of Fishes
Locomotion in Water
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Speed
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Most fishes swim maximally at ten body lengths
per second
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Larger fish therefore swims faster
Short bursts of speed are possible for a few
seconds
Mechanism
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Trunk and tail musculature propels a fish
Muscles are arranged in zigzag bands called
myomeres
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Have the shape of a W on the side of fish
Internally the bands are folded and nested
Each myomere pulls on several vertebrae
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Structural and Functional Adaptations of Fishes
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Economy
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Swimming is the most economical form of motion
because water buoys the animal
Energy cost per kilogram of body weight for
traveling one kilometer is 0.39 Kcal for swimming,
1.45 Kcal for flying, and 5.43 for walking
Yet to be determined how aquatic animals can
move through water with little turbulence
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Structural and Functional Adaptations of Fishes
Neutral Buoyancy and the Swim Bladder
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Fish are slightly heavier than water
To keep from sinking, a shark must
continually move forward
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Fins keep it “angled up”
Shark liver has a special fatty hydrocarbon,
or squaline, that acts to keep the shark a
little buoyant
Swim bladder, as a gas-filled space, is the
most efficient flotation device
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Structural and Functional Adaptations of Fishes
Hearing and Weberian Ossicles
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Fish, like other vertebrates, detect sounds as
vibrations in the inner ear.
 Weberian ossicles
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Structural and Functional Adaptations of Fishes
Respiration
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Fish gills are filaments with thin epidermal
membranes folded into plate-like lamellae
Gills are inside the pharyngeal cavity and
covered with a movable flap, the operculum
Operculum protects delicate gill filaments
and streamlines body
Pumping action by operculum helps move
water through gills
Although it appears pulsatile, water flow over
gills is continuous
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Structural and Functional Adaptations of Fishes
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Water flow is opposite to the blood flow
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Countercurrent exchange maximizes exchange of
gases
Some bony fishes remove 85% of the oxygen
from water passing over gills
Some active fishes use ram ventilation
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Forward movement is sufficient to force water
across gills
Such fishes are asphyxiated in a restrictive
aquarium even if the water is saturated with
oxygen
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Structural and Functional Adaptations of Fishes
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Fishes Out of Water
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Lungs of lungfishes allow them to respire in air
Eels can wriggle over land during rainy weather
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Use skin as major respiratory surface
A bowfin uses gills at cooler temperatures and
lung-like swim bladder at higher temperatures
Electric eel has degenerate gills and gulps air
through vascular mouth cavity
Indian climbing perch spends most of its time on
land, breathing air in special chambers
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Structural and Functional Adaptations of Fishes
Osmotic Regulation
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Freshwater is hypotonic to fish blood
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Water enters body and salt is lost by diffusion
Scaled and mucous-covered body is mostly
impermeable, but gills allow water and salt fluxes
Freshwater fishes are hyperosmotic
regulators
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Opisthonephric kidney pumps excess water out
Special salt-absorbing cells located in epithelium
actively move salt ions from water into fishes’
blood
Systems are efficient
 Freshwater fish devote little energy to
maintaining osmotic balance
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Structural and Functional Adaptations of Fishes
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About 90% of bony fishes are restricted to
either freshwater or seawater habitats
Marine bony fishes are hypoosmotic
regulators
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Blood is hypotonic to seawater
Tend to lose water and gain salt
 Risks “drying out”
To compensate for water loss, a marine teleost
drinks seawater
 Brings in more unneeded salt
 Carried by blood to gills and secreted by
special salt-secretory cells
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Structural and Functional Adaptations of Fishes
Feeding Behavior
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Fish devote most of their time searching for
food to eat and eating
With the evolution of jaws
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Most fish are carnivores
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Fish left a passive filter-feeding life and entered a
predator-prey battle
Feed on zooplankton, insect larvae, and other
aquatic animals
Most fish do not chew food
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Would block water flow across the gills
Blue fin tuna
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Structural and Functional Adaptations of Fishes
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A few can briefly crack prey items with teeth,
or have molar-like teeth in throat
Most swallow food whole
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Some are herbivores
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Easy with water pressure that sweeps food in
when the mouth opens
Eat plants and algae
Crucial intermediates in food chain
Suspension feeders
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Crop abundant microorganisms of the sea
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Structural and Functional Adaptations of Fishes
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Many plankton feeders swim in large schools
and using gill rakers to strain food
Omnivores feed on both plants and animals
Scavengers feed on organic debris
Detritovores consume fine particulate
organic matter
Parasitic fishes suck body fluids of other
fishes
Digestion follows the vertebrate plan
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A few lack stomachs
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Structural and Functional Adaptations of Fishes
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Intestine tends to be shorter in carnivores
and long and coiled in herbivores
Stomach primarily stores food
Intestine digests and absorbs nutrients
Teleost fishes have pyloric ceca
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Apparently for fat absorption
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Structural and Functional Adaptations of Fishes
Homing Salmon
 Salmon are anadromous
 Grow up in sea but return to freshwater to
spawn
 6 species of Pacific salmon and 1 Atlantic
salmon migrates
 Atlantic salmon makes repeated spawning
runs
 Pacific species spawn once and die
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Structural and Functional Adaptations of Fishes
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Pacific species of sockeye salmon
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Migrates downstream
Roams the Pacific for 4 years
Returns to spawn in headwaters of parents’
stream
Young fish are imprinted on odor of their stream
May navigate to stream mouth by sensing
magnetic field of the earth or angle of the sun,
and then smelling their way home
Salmon are endangered by stream
degradation from logging, pollution and
hydroelectric dams
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Structural and Functional Adaptations of Fishes
Reproduction and Growth
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Most fishes are dioecious with external
fertilization and external development
Guppies and mollies represent
ovoviviparous fish that develop in ovarian
cavity
Some sharks are viviparous with some kind
of placental attachment to nourish young
Most oviparous pelagic fish lay huge
numbers of eggs
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Female cod may release 4–6 million eggs
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Structural and Functional Adaptations of Fishes
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Near-shore and bottom-dwelling species lay
larger, typically yolky, nonbuoyant and
adhesive eggs
Some bury eggs
Many attach eggs to vegetation
Some incubate eggs in their mouth
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Structural and Functional Adaptations of Fishes
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Many benthic spawners guard eggs
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Freshwater fishes produce nonbuoyant eggs
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Male is usually the guard
The more care provided, the fewer the eggs
produced
Freshwater fishes may have elaborate mating
dances before spawning
Egg soon takes up water, the outer layer
hardens and cleavage occurs
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Structural and Functional Adaptations of Fishes
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Blastoderm develops and yolk is consumed
Fish hatches carrying a semitransparent yolk
sac to supply food until it can forage
Change from larva to adult may be dramatic
in body shape, fins, color patterns, etc.
Growth is temperature dependent
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Warmer fish grow more rapidly
Annual rings on scales, otoliths, etc. reflect
seasonal growth cycles
Most fish continue to grow throughout life
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