THE STEINHART AQUARIUM - Gulf of Guinea Science ...

98 A Docent Field Guide to the Species of the Steinhart Aquarium
especially Mississippi River and its tributaries.
Habitat: Prefers deep pools in large rivers where
the current is slow; is highly mobile and has been
known to travel more than 2,000 miles.
Appearance: Grey above, white below. Extended
upper jaw (rostrum) flattened into paddleshape,
accounts for 1/3 of total body length. Fins
stiffer than those of teleost fishes. Heterocercal
tail. Skeleton cartilaginous, skin tough, scales
lacking. Max length 221 cm; max weight 90.7
kg, average weight considerably less.
Reproduction and Development: Female
swims upriver to spawn, lays 2 eggs at a time.
Egg cases rounded. Eggs hatch in 7 days; young
are swept downstream to permanent home.
Diet: Zooplankton, the majority being water
fleas; also tiny crustaceans and larvae.
Predators: Only man.
Conservation Status: IUCN: Vulnerable.
Threatened by overfishing throughout much of
its range, particularly for its eggs since the ban
on imported caviar. Dams prevent fish from
reaching spawning grounds, sedimentation
and river modifications destroy habitat.
Remarks: To feed, the fish swims with its huge
mouth wide open. As the water passes over its
gills food is filtered out by special filaments
called gill rakers.
What is the paddle used for? Its broad,
flat shape acts as a rudder keeping the fish
stabilized and provides lift as the animal
moves slowly through the water filtering out
its planktonic diet.
Also, the paddle is covered with pores that
extend over the head and along the gill covers.
These pores are electroreceptors capable of
detecting as little as 1/100 of 1-millionth
volt per cm, enough to sense the presence of
plankton, a valuable tool especially as vision,
hearing and smell are poor.
ORDER LEPISOSTEIFORMES
(GARS)
Alligator Gar
Atractosteus spatula (Lepisosteidae)
Gars
Distribution: Rivers draining to the Gulf of
Mexico.
Habitat: Freshwater streams and rivers. Also
found in brackish water.
Appearance: Alligator-like. Large size and
broad, short, wide, blunt snout. Light dorsal
stripe. Dark olivaceous brown above and white
to yellowish beneath. Dark brown blotches
on all fins. Body is covered with armor-like
ganoid scales, diamond-shaped, interlocking,
and extremely hard. Head protected by bony
plates. Conspicuous teeth. Length to more than
3 m, weight to 137 kg.
Diet: Depending on which source you consult,
alligator gars are either passive, superb
lie-in-wait predators or aggressive voracious
carnivores of fish, notorious for destroying
fishnets and gulping their contents. They are
all of the above! Adult gars feed primarily on
fish, but have been found also to consume blue
crabs, birds, reptiles, amphibians, and small
mammals. Also known to scavenge.
Reproduction: Eggs laid on aquatic vegetation,
to which they adhere. Young cling to the
stems with an adhesive disc on their head until
yolk sac is absorbed, and then swim actively.
Juveniles feed on plankton, invertebrates, amphibians,
and fish before transitioning to fish
almost exclusively.
Mortality/Longevity: Females generally larger
and longer lived than males. Some may live to
50 years or more in the wild, 80 years in captivity.
Our oldest gars are 60.
Conservation Status: Not on IUCN Red List.
Pollution and degradation of habitat threaten
this species.
Remarks: One of the largest freshwater fish in
North America.
Alligator gars have two rows of teeth, a longer
one on the palate, and an outer row in the jaw,
enabling them to pierce and hold prey. Take a
look when one of these big fish “yawn.”
Gars also have a highly vascularized swim
bladder that enables them to breathe in air, an
adaptation to life in water with low oxygen
levels.
Fished intensively by professional and sports
fisherman and marketed as a food fish.
Fish eggs are poisonous to humans.
Native Americans used armor-like ganoid
scales as arrowheads and jewelry. Early
American farmers used the scales on the blades
of their plows.