Fishes are the most ancient group of vertebrates, first appearing 530 million years ago. They are highly diverse with over 28,000 living species. Fishes are aquatic and have adapted various anatomical features for aquatic life including scales, fins, buoyancy control and efficient gill respiration. Major groups include jawless fishes, cartilaginous fishes like sharks, and bony fishes including the dominant ray-finned fishes and rare lobe-finned fishes like lungfishes and coelacanths.

1. Fishes
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2. Fishes
Of vertebrates the most:
- Ancient group
- Appeared 530 MY ago
- Small, bottom-dwelling animals
without jaws, teeth, or paired fins
- Only vertebrates for 50 MY
- Evolved fins and then bony armor
- Most fish lost armor
- Diverse group
- 28,000 species
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3. Fishes
All aquatic and highly adapted for aquatic life
- Virtually all fresh and marine waters
- None are terrestrial, although some can tolerate periods of dry air
Variety of sizes
- Smallest vertebrate (0.7 cm)
- Whale shark (15 m)
- Most will continue to grow throughout lifetime
- Growth is temperature dependant (higher temp = larger size)
- Annual rings in scales, otoliths (ear bone), and other boney parts
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4. Fishes
Skin has both epidermis and dermis
- Epidermis secretes slimy mucus (reduces friction)
- Dermis produces scales
- Scales of the same material as our teeth (form of emamel)
Skeleton begins as cartilage and replaced by bone in
most
- Ribs and appendicular skeleton present
- Pectoral and pelvic fins
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5. Fishes
Movement
- Bundles of segmented muscle tissue (myomeres)
- Have W-shaped arrangement
- Mostly used for swimming
- Very efficient form of locomotion (don’t have to fight gravity)
- Myomeres produce s-shaped swimming motion
- Fish push on water
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6. Fishes
Feeding and Digestion
- Jawlessness restricted fish to deposit and filter feeding (some scavenging)
- Jaws allow for a predatory lifestyle
- Small, sharp teeth
- Produced throughout lifetime
- Flexible jaws engulf large prey
- Prey swallowed whole
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7. Fishes
Respiration
- Most have gills (more efficient than
other aquatic animals)
- Some have cutaneous respiration
- Some can breathe air
Circulation
- 2 chambered heart with single
circuit
- Blood pumped through gills then to body
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8. Fishes
Nervous system
- Small brain compared to other vertebrates
- Cerebrum - high center (very small)
- Cerebellum - coordination of movement (relatively
large)
- Brain stem - automatic activities (relatively large)
- Sense organs
- Evolved because light doesn’t travel far in water
and sound and pressure waves travel very far
- Lateral line system
- Eyes
- Chemoreceptors
- Hearing
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9. Fishes
Excretion
Kidneys for nitrogenous
wastes (osmoregulation too)
● Primitive marine fishes are
isotonic
● Most marine fishes are
hypotonic
○ Loose water and gain salt
● Freshwater fishes are
hypertonic
○ Gain water and loose salts
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10. Fishes
Reproduction and Development
- Most dioecious
- Most with external fertilization
- Marine fish reproduce in large schools
- Freshwater fish have elaborate mating
- Some with a high degree of parental care
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11. Fishes
Groups of fish
1. Jawless fishes (Agnatha)
○ 111 species
2. Cartilaginous fishes
(Chondrichthyes)
○ 970 species
3. Bony fishes (Osteichthyes)
○ 27,000 species
○ Separated into ray-finned
(Actinopterygii) and lobe-
finned (Sarcopterygii)
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12. Superclass Agnatha
Jawless fishes
Common features
- Lack:
- Jaws
- Internal bones
- Scales
- Paired fins
- Porelike gill openings
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13. Superclass Agnatha
Class Myxini - hagfishes
- Entirely marine
- Feed on annelids, crustaceans, or
decaying animals
- Almost blind
- Keen sense of smell
- Attracted to dead whales and fish
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14. Superclass Agnatha
Class Myxini - hagfishes
- Two toothed plates on tongue that
grasp prey
- May tie knot with body for leverage
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15. Superclass Agnatha
Class Myxini - hagfishes
- Generate slime to ward off
predators
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16. Superclass Agnatha
Class Myxini - hagfishes
- Bodies are isotonic with seawater
- Primary heart with three accessory
hearts
- Reproductive biology largely a
mystery
- Few, large eggs
- No larval stage
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17. Superclass Agnatha
Class Petromyzontida - lampreys
- 50% are parasitic
- Others do not feed as adults
- Anadromous - ascend freshwater
rivers to breed
- Adults marine
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18. Superclass Agnatha
Class Petromyzontida - lampreys
- Reproduction
- Males build nest in spring/summer
- Females shed eggs and males sperm
- Die shortly after
- Eggs adhere to stones and pebbles
- Larvae hatch 2 weeks later
- Leave nest and burrow into substrate
- Live as filter feeders for 3-7 years
- Metamorphosize into adults
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19. Superclass Agnatha
Class Petromyzontida - lampreys
- Feeding
- Parasitic forms attach to host
- Rasp wound with tongue
- Inject anticoagulant to prevent clotting
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20. Superclass Gnathostomata
Jaws represent a major advancement
for vertebrates
- Freed from bottom feeding
- Longer list of feeding
opportunities
Evolved from gill arches
- In primitive fish resemble gill
arches
- Still occurs in shark development
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21. Superclass Gnathostomata
Paired fins
- Pelvic and pectoral
- Stabilization during swimming
- Began as skin folds?
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22. Superclass Gnathostomata
Class Chondrichthyes
- 970 species
- All but a few are marine
- Include the largest fish
- Body fusiform (sharks) or
flattened (skates and rays)
- Generally with tough, leathery
skin
- Placoid scales
- Skeleton is cartilaginous
- Teeth are mineralized
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23. Superclass Gnathostomata
Class Chondrichthyes
- Elasmobranchii - sharks, skates, and rays
- Sharks
- Heterocercal tail - vertebrae extend into the dorsal lobe of the caudal fin
- Paired pectoral and pelvic fins
- Dorsal fin
- Paired nostrils
- Claspers in males
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24. Superclass Gnathostomata
Class Chondrichthyes
- Elasmobranchii - sharks, skates,
and rays
- Sharks
- Well developed senses (needed to be
an efficient predator)
- Olfactory organs used to long-
distance detection
- Lateral line used at moderate
distances
- Vision and ampullae of Lorenzini
used at close distances
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25. Superclass Gnathostomata
Class Chondrichthyes
- Elasmobranchii - sharks,
skates, and rays
- Sharks
- Reproduction may be oviparous,
ovoviviparous, or viviparous
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https://youtu.be/KW8PKZF53bQ

26. Superclass Gnathostomata
Class Chondrichthyes
- Elasmobranchii - sharks, skates, and rays
- Skates and rays
- Half of all elasmobranchs
- Dorsoventrally flattened
- Enlargement of the pectoral fins
- Specialized for bottom dwelling
- Some rays have venomous spines on tail
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27. Superclass Gnathostomata
Class Chondrichthyes
- Holocephali - chimaeras or ratfish
- Split from elasmobranchs 380 MYA
- Jaws bear flat plates instead of teeth
- Upper jaw completely fused to cranium
- Gills covered by single operculum
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28. Superclass Gnathostomata
Class Chondrichthyes
- Holocephali - chimaeras or ratfish
- Split from elasmobranchs 380 MYA
- Jaws bear flat plates instead of teeth
- Upper jaw completely fused to cranium
- Gills covered by single operculum
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29. Superclass Gnathostomata
Clade Osteichthyes - bony fishes
- Class Actinopterygii - ray-finned
fishes
- Every fish you’ve eaten, caught, seen,
owned,...etc.
- Class Sarcopterygii - lobe-finned
fishes
- Much rarer
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30. Superclass Gnathostomata
Class Actinopterygii
- 31,000 species
- Four clades recognized
- Birchirs - have lungs and ganoid scales.
Restricted to west Africa (ex: African
lungfish)
- Chondrosteans - 27 species of freshwater or
anadromous fish (sturgeon, paddlefish)
- Neopterygians - heavy scaled and boned
fishes with well developed swim bladder
(bowfin, gars)
- Teleosts - modern bony fishes
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31. Superclass Gnathostomata
Class Actinopterygii
- Teleosts evolved several morphological characters that allowed them to
become so dominant and diverse
- Heavy dermal armour (i.e., ganoid scales) was replaced by lighter scales (e.g., cycloid,
ctenoid)
- Faster swimmers (better at being a predator and avoiding predators)
- Symmetrical tail replaced heterocercal tail
- Faster swimming ability (all force directed backwards evenly)
- Other fins were made more flexible and adapted for other uses
- I.e., lure in angler fishes, venom-delivering spines in scorpionfishes
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32. Superclass Gnathostomata
Class Actinopterygii
- Teleosts evolved several
morphological characters that
allowed them to become so
dominant and diverse
- Refinement of the swim bladder
- Better buoyancy control
- Changes to the jaw to allow for
suction feeding, protrusion of the jaw,
and pharyngeal jaws
- Wider array of prey items
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33. Superclass Gnathostomata
Class Sarcopterygii
- Possessed lungs and gills
- Ancestrally had heterocercal tail, but diphycercal tail is derived condition
- Powerful jaws, enameled scales, and fleshy paired lobed fins
- Possibly used for locomotion
- 8 species remain
- 6 lungfishes; 2 coelacanths
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34. Superclass Gnathostomata
Class Sarcopterygii
- Lungfishes vary in their ability to
withstand terrestrial environments
- Australian lungfishes rely on gills
- South American and African lungfishes
can live out of water for long periods
- Can even survive drying of their
body of water is able to burrow
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35. Superclass Gnathostomata
Class Sarcopterygii
- Coelacanths
- Once only known from fossils
- Discovered living in 1938
- Two species - one near
Madagascar, one near
Philippines
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https://youtu.be/rYOf2wIoxgo