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Superclass Osteichthyes: Bony Fishes n  2 major classes

n  Ray-finned fishes, class Actinopterygii, radiated to form modern bony fishes

n  Lobe-finned fishes, class Sarcopterygii, include lungfishes and the coelacanth

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n  Modern Day Bony Fish n  Constitute 96% of all living

fishes and half of all vertebrates

n  Range from 10 millimeters to 17 meters long, and up to 900 kilograms in weight

n  Some can live in hot springs at 44o C (111.2oF) while others survive under Antarctic ice at - 2o C (28.4oF)

n  Some live in salt concentrations three times seawater

n  Others found swamps devoid of oxygen

Class Actinopterygii: Ray-finned Fishes

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n  Heavy dermal armor replaced by light, thin, flexible cycloid and ctenoid scales n  Some eels, catfishes, and others

lost scales n  Increased mobility to avoid

predators and improve feeding efficiency

n  Provide greater mobility and serve a variety of functions n  Braking, streamlining, and social

communication n  Homocercal tail allowed greater

speed and buoyancy n  Jaw changed to increase suctioning

and protrusion to secure food

Class Actinopterygii: Ray-finned Fishes

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Structural and Functional Adaptations of Fishes

Locomotion in Water n  Mechanism

n  Trunk and tail musculature propels a fish using undulations and/or the fins.

n  Muscles are arranged in zigzag bands called myomeres n  Have the shape of a W on the side of fish n  Internally the bands are folded and nested n  Each myomere pulls on several vertebrae

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Neutral Buoyancy and the Swim Bladder

n  Fish are slightly heavier than water

n  To keep from sinking, a shark must continually move forward

n  Shark liver has a special fatty hydrocarbon, or squaline, that acts to keep the shark a little buoyant

n  Swim bladder, as a gas-filled space, is the most efficient flotation device n  Fish controls depth by

adjusting volume of gas in swim bladder

Structural and Functional Adaptations of Fishes

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Hearing and Weberian Ossicles

n  Fish, like other vertebrates, detect sounds as vibrations in the inner ear.

Structural and Functional Adaptations of Fishes

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Respiration n  Fish gills are filaments with plate-

like lamellae n  Gills are covered with a movable

flap, the operculum for protection and to streamline the body

n  Pumping action by operculum helps move water through gills

n  Water flow over gills is continuous n  Water flow is opposite to the

blood flow to maximize gas exchange

n  Some active fishes use ram ventilation to force water across gills

Structural and Functional Adaptations of Fishes

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Osmotic Regulation n  Freshwater fish have tissue with a

high salt concentration n  Kidney works to pumps excess

water out n  Special salt-absorbing cells

actively move salt ions from water into fishes’ blood

n  Marine bony fishes have tissue with low salt concentration n  Tend to lose water and gain

salt n  Risks “drying out”

n  To compensate for water loss, a marine fish drinks seawater n  Brings in more unneeded

salt n  Carried by blood to gills

and secreted by special salt-secretory cells

Structural and Functional Adaptations of Fishes

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Feeding Behavior n  Most fish are carnivores

n  Feed on zooplankton, insect larvae, and other aquatic animals

n  Most fish do not chew food which would block water flow across the gills

n  A few can crack prey items teeth or have molar-like teeth

n  Most swallow food whole n  Easy with water pressure that

sweeps food in when the mouth opens

n  Others are herbivores, suspension feeders, omnivores, scavengers, detritivores, or parasites

Structural and Functional Adaptations of Fishes

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Reproduction and Growth n  Most fishes are dioecious with external

fertilization and external development n  Guppies and mollies represent ovoviviparous

fish that develop in ovarian cavity n  Some sharks are viviparous with some kind

of placental attachment to nourish young n  Most oviparous pelagic fish lay huge

numbers of eggs n  Female cod may release 4–6 million eggs

Structural and Functional Adaptations of Fishes