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The shape of fish is dictated by the properties of water and the lifestyle of the fish - PowerPoint PPT Presentation

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Head Trunk Tail . Pectoral fins Pelvic fins Nape Lateral line Dorsal fin spiny dorsal soft dorsal Vent (anus). Snout Mouth Nares Eye Operculum Branchiostegal membrane. Caudal fin Caudal peduncle Adipose fin Anal fin.

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Head Trunk Tail

Pectoral fins

Pelvic fins


Lateral line

Dorsal fin

spiny dorsal

soft dorsal

Vent (anus)






Branchiostegal membrane

Caudal fin

Caudal peduncle

Adipose fin

Anal fin

The shape of fish is dictated by the properties of water and the lifestyle of the fish

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Basic body shapes

Fusiform – streamlined, elliptical in cross-section, narrow peduncle


Compressiform – similar to fusiform but laterally compressed


Depressiform – body flattened from top to bottom

skates and rays – NOT FLOUNDER

Sagittiform - elongated body, dorsal and anal positioned posteriorly.


Anguilliform – long snake-like body – attenuated

eels, lampreys

globiform – short round body – truncated

puffer fish

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Body shape often indicates the lifestyle of the fish

Rover-predator – actively swims to find prey – streamlined, terminal mouth, forked tail – bass, trout

Lie-in-wait predators/ ambush predators – sagittiform body, rapid acceleration - muskellunge

Surface-oriented fish – depressed head, superior mouth, dorsal fin posterior – mosquitofish, top-minnows

Bottom fish - depressed head, subterminal mouth, barbels common - catfish

Deep-bodied “Pickers”- compressiform body, short head, large eye, paired fins anterior (pect high on body),

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Mouth orientation

superior – up turned

terminal - front

inferior – below

The mouth is often protusible – forms a tube for suction feeding


Dorsal and Anal fins – used for stability in swimming

Two dorsals (spiny, soft) is a derived trait

Caudal fins

Heterocercal – unequal lobes

Homocercal – equal lobes

Isocercal – no lobes

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Pelvic fin – may be positioned forward in derived fishes (abdominal, thorasic, jugular)

Pectoral fin – may be positioned higher and oriented vertically on body in derived fishes, used to grasp substrate in some benthic species (Cottus). Modified as wings in flying fish

Adipose fin – fleshy fin between dorsal and caudal

– vestigal? primitive characteristic

Spines at the origin of dorsal, anal, pelvic, pectoral fins is a derived trait

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Other body characteristics (abdominal, thorasic, jugular)

Scales – support and protect outer covering

skin is waterproof, protects from parasites

Placoid scales – Chondrichthyan fishes large

dentin, very thick

Ganoid scales –gar – diamond shaped, ganoin

Teleosts (derived bony fishes) ossified

Cycloid – circular scales with a smooth edge

Minnows and suckers

  • Ctenoid – derived characteristic, exposed portion of scale has small projections that “rough up” the surface of the fish – aids in making the fish hydrodynamic (think golf ball) sunfishes, darters

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Scales – continued (abdominal, thorasic, jugular)

Fish scales are dermal and covered by an epidermis

– up to 30 cells thick. Epidermis contains mucus glands.

Scales grow in an asymmetric pattern

focus – center of growth

circuli – bony ridges

annuli – thickened ridge

used for age determination

Scales that are lost or damaged can be quickly replaced – inner area contains no information about growth.

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Gas bladder (abdominal, thorasic, jugular)

saltwater fish bladder 5-6 % of volume

freshwater 7-10%

Physostomes - bladder connected to esophagus by pneumatic duct – ancestral condition

Gas is forced into the bladder by gulping air and buccal contraction.

Fishes with physostomous bladder are usually found near surface.

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Physoclists - bladder not connected to esophagus (abdominal, thorasic, jugular)

Gas gland with (rete mirabile)

– secrete gas from blood

Oval – absorbs gas back to

blood stream

Some other fishes have reduced bladders (fast water) or no bladder (benthic)

Circulation and Respiration

Oxygen - air is 21% oxygen

partial pressure .21 * 760 (1 atmosphere) = 159.6 mm Hg

296 mg Oxygen/ liter (ppm)

Water has low oxygen solubility

at 5 C, water holds 12.76 mg oxygen/l (4.3% of air)

Temperature, pressure, and total dissolved solids affect solubility:

at 35 C, water holds 6.94 mg oxygen/l (2.3% of air)

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Circulation (abdominal, thorasic, jugular)

Gill structure

gill arch

gill filaments


Blood flow/ Water flow - Counter current orientation

Teleosts usually have four functional gills

Pseudobranch – 1st gill arch (visceral arch) is attached to operculum

– receives oxygenated blood

4 pair of branchial arches - respiratory

Pharyngeal arch – last element – may contain pharyngeal teeth - Cyprinids

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Gill ventilation – buccal/ opercular pump (abdominal, thorasic, jugular)

– ram ventilation

paddlefish, tunas, billfish

Alternative modes of respiration

Cutaneous – more important for larvae,

eels, bullhead catfish, walking catfish (Clarias),

Respiratory tree/ labyrinthine organ – modified gill, does not collapse when exposed to air

walking catfish, snakeheads

Vascularized tissue:

in mouth – electric eel, snakeheads

chambers off esophagus – lungfishes, bowfin, gar

stomach – South American catfishes

Obligate air breathers – Clarias, snakeheads, Arapaima, lungfishes,

Facultative air breathers – gar, bowfin, American eels