fish - north medford high school science mr....

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CHAPTER 24

Fish

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Diversity Overview n  Modern fish

n  Aquatic vertebrate with gills, limbs (if present) in the form of fins, and usually with a skin covered in scales of dermal origin

n  Approximately 24,600 living species n  Adapted to live in medium 800 times denser than air n  Gills are efficient at extracting oxygen from water that has

1/20 the oxygen of air n  Lateral line system detects water currents and vibrations, a

sense of “distant touch”


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Living Jawless Fishes

Overview n  Living jawless fishes include hagfishes and lampreys

n  Members of both groups lack jaws, internal ossification, scales, or paired fins

n  Both groups share pore-like gill openings and an eel-like body


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Class Myxini: Hagfishes n  Entirely marine n  Scavengers and predators of

annelids, molluscs, dead or dying fishes, etc.

n  Enters dead or dying animal through orifice or by digging inside using keratinized plates on tongue

n  Nearly blind n  Locate food by an acute

sense of smell and touch n  To provide leverage

n  Ties knot in tail and passes it forward to press against prey

n  Special glands along body secrete fluid that becomes slimy in contact with seawater



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n  Body fluids are in osmotic equilibrium with seawater

n  Circulatory system includes three accessory hearts in addition to a heart behind gills

n  Reproduction of Hagfishes n  In some species, females outnumber males by

100 to 1 n  Females produce small numbers of large, yolky

eggs 2-7 centimeters in diameter



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Class Petromyzontida: Lampreys n  Diversity

n  All lampreys in Northern Hemisphere belong to the family Petromyzontidae

n  Marine lamprey Petromyzon marinus n Occurs on both Atlantic coastlines n Grows to a length of one meter

n  20 species of lampreys in North America n Half belong to non-parasitic brook-dwelling

species



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n  Reproduction and Development n  Ascend freshwater streams to

breed n  Marine forms are anadromous

n  Leave the sea as adults to spawn upstream

n  In North America n  All spawn in winter or

spring n  Males build nest by lifting

stones with oral discs and using body vibrations

n  Female anchors to a rock and male attaches to her head

n  As eggs are shed into nest, the male fertilizes them

n  Adults die soon thereafter



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n  Eggs hatch in two weeks into ammoceotes larvae n  Lives first on yolk supply and

drifts downstream to burrow into sandy areas

n  Suspension-feeder until it metamorphoses into an adult

n  Change to an adult involves eruption of eyes, keratinized teeth replacing the hood, enlargement of fins, maturation of gonads and modification of gill openings



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n  Parasitic Lampreys n  Marine, parasitic lampreys migrate

to the sea n  Other species remain in freshwater n  Attach to a fish by a sucker-like

mouth n  Sharp teeth rasp through flesh as

they suck fluids n  Inject anticoagulant into a wound n  When engorged, lamprey drops off

but wound may be fatal to fish n  Parasitic freshwater adults live 1–2

years before spawning and dying n  Anadromous forms live 2–3 years n  Nonparasitic lampreys do not feed

n  Digestive tract degenerates as an adult

n  They spawn and die



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Class Chondrichthyes: Cartilaginous Fishes

Overview n  About 970 living species n  Well-developed sense organs, powerful jaws,

and predaceous habits helped them survive n  True bone is completely absent throughout

the class n  Nearly all are marine

n  Only 28 species live primarily in freshwater n  After whales, sharks are the largest living

vertebrates, some reaching 12 meters in length


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Subclass Elasmobranchii: Sharks, Skates and Rays n  13 living orders of elasmobranchs with

about 937 total species described n  Order Carcharhiniformes

n  Contains the coastal tiger and bull sharks and the hammerhead

n  Order Lamniformes n  Contains large, pelagic sharks such

as the white and mako shark n  Order Squaliformes

n  Contains dogfish sharks n  Order Rajiformes

n  Contain skates n  Order Myliobatiformes

n  Contains several groups of rays (stingrays, manta rays, etc.)



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n  Form and Function n  Sharks are among the most gracefully streamlined of fishes

n  Body is fusiform n  Thrust and lift provided by an asymmetrical heterocercal tail

n  Vertebral column turns upward and extends into dorsal lobe of caudal fin

n  Fins include n  Paired pectoral and pelvic fins n  One or two median dorsal fins n  One median caudal fin n  Sometimes a median anal fin



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n  In males, the medial part of the pelvic fin is modified to form a clasper used in copulation

n  Paired nostrils are anterior to mouth n  Lateral eyes are lidless n  Behind each eye is a spiracle

n  Remnant of the first gill slit n  Tough, leathery skin with placoid scales

n  Reduce water turbulence n  Detect prey at a distance by large olfactory organs sensitive to

one part per 10 billion



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n  Nostrils to each side of the hammerhead shark may improve stereo-olfaction

n  Prey may also be located from long distances sensing low frequency vibrations in the lateral line

n  At close range, switch to vision n  Most have excellent vision even in dimly lit water

n  Up close, sharks are guided by bioelectric fields that surround all animals

n  Electroreceptors, the ampullae of Lorenzini, are located on the shark’s head



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n  Upper and lower jaws equipped with sharp, triangular teeth that are constantly replaced

n  Mouth opens into large pharynx, containing openings to gill slits and spiracles

n  Short esophagus runs to stomach n  Liver and pancreas open into short, straight intestine n  Spiral valve in intestine slows passage of food and

increases absorptive area n  Rectal gland secretes NaCl and assists the kidney n  Heart chambers provide standard circulatory flow through

gills and body



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n  Reproduction and Development n  Fertilization is internal n  Maternal support of embryo is variable

n  Includes oviparous, ovoviviparous, and viviparous species

n  “Mermaid’s purse” n  Horny capsule encasing eggs laid by some oviparous

species


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