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

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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
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 trout
Compressiform similar to fusiform but laterally
compressed crappie
Depressiform body flattened from top to
bottom skates and rays NOT FLOUNDER
Sagittiform - elongated body, dorsal and anal
positioned posteriorly. muskellunge
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
Fins
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
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 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 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 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 Gill structure gill arch gill
filaments lamella
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 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