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Fishes. Chapter 24. I. Diversity. 26,000 living species—more species than all other vertebrate groups combined Adapted to live in a medium 800 x more dense than air Can adjust to salt and water balance of environment Gills extract oxygen from water that has 1/20 th the oxygen of air

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Chapter 24

i diversity
I. Diversity
  • 26,000 living species—more species than all other vertebrate groups combined
  • Adapted to live in a medium 800 x more dense than air
  • Can adjust to salt and water balance of environment
  • Gills extract oxygen from water that has 1/20th the oxygen of air
  • Aquatic environment both shaped and constrained their evolution
ii ancestry and evolution
II. Ancestry and Evolution
  • A. Ancestor
    • Descended from free-swimming protochordate ancestor
  • B. Agnathans
    • Earliest fish-like vertebrates
    • Include extinct ostracoderms, and living lampreys and hagfishes
  • C. Placoderms
    • Fish with paired appendages and jaws that went extinct in Carboniferous with no living descendants
D. & E.
  • D. Cartilaginous Fishes
    • Lost heavy armor and adopted cartilage as skeleton
    • Flourished during some periods, becoming nearly extinct during others
  • E. Acanthodians
    • Resemble bony fish but have heavy spines on all but caudal fin; sister group to bony fishes
    • Went extinct in lower Permian
f bony fishes
F. Bony Fishes
  • Dominant fishes today
  • 2 distinct lineages—ray finned and lobe finned
  • Ray-finned radiated to form modern bony fishes
  • Lobe-finned include lungfishes, the coelacanth, and are sister group to tetrapods (amphibian ancestors)
iii superclass agnatha jawless fishes
III. Superclass Agnatha: Jawless Fishes
  • A. Characteristics
    • Lack jaws, internal ossification, scales, or paired limbs
    • Pore-like gill openings and eel-like body
b class myxini hagfishes
B. Class Myxini: Hagfishes
  • 43 species
  • Entirely marine
  • Scavengers and predators of annelids, molluscs, dead or dying fishes, etc
  • Nearly blind but locates food by acute sense of smell
  • Rasps hole into prey then eats from inside out with plate-like tongue
  • Glands secrete substance that becomes slimy in contact with seawater
c class cephalaspidomorphi
C. Class Cephalaspidomorphi
  • 1. Diversity
    • 41 species; 22 in North America and of these, half are non-parasitic brook variety
    • Marine lampreys can grow to length of 1 m.
    • All lampreys reproduce in freshwater streams, dying soon after
2 parasitic lampreys
2. Parasitic Lampreys
  • Attach to fish by sucker-like mouth and sharp teeth rasp away flesh
  • Anticoagulant injected into wound to stimulate flow of blood
  • Wound may be fatal to host fish
  • Non-parasitic lampreys do not feed; digestive system degenerates and fish die after reproducing, within 2-3 years
3 sea lamprey invasion
3. Sea Lamprey Invasion
  • No lampreys existed in Great Lakes prior to 1829 when shipping canals were built
  • By the 1940’s, they existed in all the lakes
  • They decimated almost all fish species until populations finally declined due to lack of food and control measures
iv class chondrichthyes
IV. Class Chondrichthyes
  • A. Overview
    • 850 species nearly all marine; 28 species live in freshwater
    • Ancient lineage but have survived due to well-developed sense organs and powerful jaws making them successful predators
    • Largest living vertebrates, after whales, reaching up to 12 m in length

Whale shark reaches 43’ in length

b subclass elasmobranchii
B. Subclass Elasmobranchii
  • 1. Sharks
    • A. Orders
      • Carcharhiniformes—tiger and bull sharks which are coastal sharks and the hammerhead
      • Lamniformes-- white and mako sharks which are large pelagic sharks
      • Squaliformes—some of these are deep sea dwellers like dogfish sharks
      • Orectolobiformes—carpet sharks like bamboo, nurse, and whale sharks
b outer physiology
b. Outer Physiology
  • Streamlined fusiform body shape
  • Pointed nose with paired nostrils in front of ventral mouth; on hammerhead, nostrils on ends of “hammer”
  • Lateral eyes without lids
  • Tail has longer upper lobe (heterocercal)
  • Paired pectoral and pelvic fins, 1-2 dorsal fins, 1 caudal fin, and sometimes an anal fin
  • Tough, leathery skin with placoid scales that reduce water turbulence
c senses
c. Senses
  • Olfactory organs can detect chemicals diluted 1/10 billionth their original concentration
  • Lateral line senses low frequency vibrations of prey over large distances
  • Excellent vision, even in dim water, used at close range
  • At close range, sharks are guided to prey by electric fields surrounding all animals
d inner physiology
d. Inner Physiology
  • Sharp triangular teeth in upper and lower jaws; arranged in rows that are constantly replaced
  • Mouth leads to pharynx with openings to gill slits
  • Osmoregulation accomplished by rectal gland which secretes sodium chloride; nitrogenous compounds are also retained in blood to increase solute concentrations, making more on par with seawater
e shark attacks
e. Shark Attacks
  • Only 32 species ( of 350) have been documented to attack humans with another 36 considered potentially dangerous; these typically are the larger size sharks; 80 % of sharks are harmless
  • Great white, tiger, and bull sharks are the more aggressive species
  • 50-75 attacks occur each year, with 8-12 fatalities; in contrast 30-100 million sharks are killed every year
  • Attacks usually occur by sandbars, steep drop offs, or by river inlets and are associated with mistaken identity,territorial behavior, or feeding behavior
2 rays
2. Rays
  • A. Order
    • Rajiformes—skates, sawfish rays, electric rays, stingrays, manta rays and others
    • Make up half of all species of Elasmobranchii
b form and function
b. Form and Function
  • Specialized for benthic life
  • Flattened dorsoventrally; enlarged pectoral fins are used as swimming wings
  • Water used in respiration enters large spiracles in head
  • Teeth adapted to act as rollers to crush invertebrates and sometimes small fish
  • Stingrays have whip-like tail with spines and venom glands
  • Electric rays have electric organs on sides of head
c subclass holocephali chimeras
C. Subclass Holocephali: Chimeras
  • 31 species
  • Ratfishes
  • Diverged from earliest shark lineage
  • Mouth has flat plates for crushing invertebrates; also feeds on seaweed and small fish
d reproduction and development
Internal fertilization

Oviparous sharks and rays lay an egg capsule immediately after fertilization that attaches to kelp with tendrils; may take up to 2 years before mini adult hatches

Ovoviviparous sharks retain fertilized eggs in reproductive system where they are nourished by yolk of egg; “live” birth

Viviparous sharks nourish embryos with maternal bloodstream; “live” birth

Live births make it more likely more of the young survive but no other care is given after birth

D. Reproduction and Development
v superclass osteichthyes
V. Superclass Osteichthyes
  • A. Origin, Evolution, and Diversity
    • Lineage developed in Silurian and now accounts for 96% of all fishes and all tetrapods
    • Bone replaces cartilage as fish develops
    • Lung or swim bladder evolved from an extension of the gut; gas filled, it aids in buoyancy
    • Bony operculum, a flap covering the gills that rotates outward, draws water more efficiently over them
    • Specialization of jaw musculature improves feeding; also unique dental characters
a palaeoniscids
a. Palaeoniscids
  • Earliest forms, existing from late Silurian to late Paleozoic
  • Small, large eyes, dorsal fin with bony rays, heterocercal tail, and interlocking scales
  • Survived as other fishes declined, suggesting some adaptive advantage
  • Gave rise to the chondrosteons and the neopterygians
b chondrosteons
b. Chondrosteons
  • Most primitive characteristics
  • Heterocercal tail and ganoid scales
  • Living species include sturgeons, paddlefishes, and bichirs
c neopterygians
c. Neopterygians
  • One lineage gave rise to modern bony fishes, the teleosts
  • Living species are bowfin and gars which gulp air and use vascularized swim bladder to supplement the gills
d teleosts
d. Teleosts
  • 96 % of all living fishes; half of all vertebrates
  • 10 mm to 17 m; up to 900 kg in weight
  • Found at 5,200 m to 8,000 m below sea level
  • Some can live in hot springs at 44 oC while others can survive in Antarctic –2 oC.
  • Some live in salt concentrations three times seawater; others in swamps devoid of oxygen
2 morphological trends
2. Morphological Trends
  • Heavy armor replaced by light cycloid or ctenoid scales which made fish more mobile; some fish such as eels and catfish have completely lost scales
  • Fins changed to provide greater mobility and serve a variety of functions: braking, streamlining, and social communication
  • Homocercal tail allowed greater speed and buoyancy
  • Swim bladder switched from primarily respiratory to buoyancy in function
  • Jaw changed to increase suctioning and protrusion to secure food



c class sarcopterygii
C. Class Sarcopterygii
  • 1. Diversity
    • Only 7 species alive today; 6 lungfishes and 1 coelacanth
    • Early ones had lungs as well as gills, heterocercal tail; later tail became symmetrical
    • Skin covered in heavy scales overlaid by an enamel
    • Fleshy, paired lobes are used to scuttle along bottom
    • South American and African lungfishes can survive out of water or long periods of time
2 coelacanth
2. Coelacanth
  • Thought to have been extinct for 70 million years until one was dredged up off of coast of Africa in 1938
  • More were caught off the coast of the Comoro Islands in 1998
vi structural and function adaptations
VI. Structural and Function Adaptations
  • A. Locomotion
    • 1. Mechanism
      • Trunk and tail muscles propel fish forward by undulations
      • Large, rigid head minimizes yaw
      • Very rigid body creates less yaw and a fast fish
      • The largest fin is the tail or caudal fin for rapid forward movement.
      • Dorsal fins on the top and anal fins underneath assist with lateral stability.
      • Pectoral fins behind the gill covers (operculum) assist with hovering and slow turning.
      • Pelvic fins are often small for open water swimmers but larger on bottom dwellers which use them for resting on.
2 speed and energy
2. Speed and Energy
  • Larger fish swim faster
  • Short bursts of speed are possible for a few seconds
  • Swimming is most economical means of motion since water buoys the animal; swimming expends 0.30 Kcal, 1.45 Kcal for walking, and 5.43 Kcal for flying
b swim bladder
B. Swim Bladder
  • Fish are slightly heavier than water
  • A shark has a very fatty liver that makes it a little buoyant; must also keep swimming to move it forward and angle itself up
  • Bottom dwelling fishes also lack swim bladder
  • Fish can control depth by adjusting volume of gas in swim bladder
  • Gas gland removes or adds gases from blood to remove or add gas to bladder
  • Some fish gulp air to fill swim bladder
c respiration
C. Respiration
  • Gill filaments are folds of tissue inside the pharyngeal cavity covered by the operculum
  • Continuous water flow opposite blood flow through capillaries maximizes gas exchange allowing some fish to remove 85% of O2 from H2O
  • Some fishes are dependent on ram ventilation as well, in which forward movement pushes more water over gills; such fish will die in an aquarium
  • Lungfish use lungs; eels use skin; bowfin uses gills at low temperatures and air bladder at higher temperatures; electric eel has degenerate gills and must gulp air
d osmotic regulation
D. Osmotic Regulation
  • 1. Freshwater Fishes
    • Freshwater has less salt than blood of fish so water tends to enter fish’s cells and its salts tend to leave
    • Hyperosmotic regulators: kidney pumps out excess water and salt absorbing cells in skin remove salts from water and add to blood
    • Euryhaline fishes live in estuary environments where they are in contact with both fresh and salt water
2 marine fishes
2. Marine Fishes
  • Blood has lower salt content than surrounding water so tend to lose water and gain salt
  • Hypo-osmotic regulators: fish drinks water bringing in more water but also salt; salt is carried by blood to gills where it is secreted by salt-secretory cells, some salt leaves in feces, and others are excreted by kidneys
e feeding behavior
E. Feeding Behavior
  • Most time devoted to searching for food and eating
  • Most carnivores-feed on zooplankton, insect larvae, and other aquatic animals
  • Most don’t chew food since it would block flow of water across gills; swallow food whole although a few have teeth that crack prey or have some molars in throat
  • Some herbivores--eat plants and algae
  • Suspension feeders eat plankton, using gill rakers to strain food; these fish swim in large schools
  • Also have omnivores, scavengers, and parasites
  • Stomach used for storage; intestines absorb and digest nutrients
f migration
F. Migration
  • 1. Eels
    • Catadromous—develop in freshwater but spawn in seawater
    • Adult eels spawn in Sargasso Sea at depths of 300 m.
    • Larvae drift for 2 years before developing into elvers; males remain in brackish water; females swim hundreds of miles up rivers
    • Females mature for 8-15 years before returning to the sea ( 8 months to complete journey)
    • American eels are separate species from European eels
2 salmon
2. Salmon
  • Anadromous—living in sea but spawing in freshwater
  • 6 Pacific salmon species, and 1 Atlantic salmon species that migrate
  • Pacific species migrate downstream, live in Pacific for 4 years, and then return up the same stream it was spawned in
  • Young fish are imprinted with the odor of their stream
  • Pacific salmon spawn and then die
  • Endangered by stream degradation, logging, pollution, and hydroelectric dams
  • Most dioecious with external fertilization and development
  • Some are ovoviviparous where eggs develop in ovarian cavity—sharks, guppies, mollies
  • Oviparous marine fish lay large numbers of eggs, upwards of several million
  • Nearshore or bottom dwelling fish lay fewer, larger nonbuoyant sticky eggs
  • Some fish bury eggs, attach them to vegetation, incubate them in their mouths
  • Freshwater fish produce fewer, nonbuoyant eggs, and more care is usually provided
  • Many freshwater fish also have elaborate mating dances before spawning
h growth
H. Growth
  • Egg starts to take up water after it is laid, outer layer hardens, and cell division begins
  • Yolk is consumed during development
  • Fish fry hatch carrying semitransparent yolk sac to supply food until it can forage
  • As fry change to adult, it may undergo dramatic changes in body shape, fins, color patterns, etc
  • Growth is temperature dependent; warmer fish grow more rapidly
  • Annual rings on scales reflect seasonal growth cycles
  • Most fish continue to grow throughout life and do not stop at maturity