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There
are some 800 species of fish found in the freshwater
habitats of the Amazon and other regions of Ecuador. Only
half that number or some 450 species are found in the
Pacific ocean surrounding the mainland and the
islands. This discrepancy in numbers is due to the much higher
nutritional value found in the murky Amazon waters where
fruits, seeds and other organic materials are present in much
higher proportion compared to the much clearer waters of the
Pacific ocean.
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Fish are
very abundant in the Amazon waters and provide an
important food source for the native people there. From
the large catfish (see left photo) to smaller fish
like the oscar (see below, also valued for fish
tanks) the selection is great. A giant among Amazon fish
is Arapaima gigas, commonly called paiche in
Ecuador. It can reach 3m in length and provide thus plenty
of proteins for the lucky fisherman and his family. It
inhabits lagoons and one can observe it coming up to the
surface to breathe air. Doing so it is harped and caught.
Unfortunately in many regions it is quite rare now due to
extensive hunting them. Other well-known fish although not
for food are the electric eel which reach lengths
of 1.8m and can discharge some 650 volts, enough to stun
the biggest preys. Many species play an important role as
seed dispersers as they depend on fruits and seeds
for their diet. Some fish even feed on leaves and other
fallen detritus from the forest. |
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Most feared by many
outsiders are the piranhas. Just looking at their sharp
teeth it is not hard to imagine why. But natives are not that
much afraid and swim happily among them being more concerned about
stepping on stingrays. Piranhas do not attack and concentrate on
dead or hurt animals fulfilling roles of aquatic vultures.
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Stingrays are mostly encountered lying on sandy bottom
in often shallow waters. On some sandy ocean beaches in Ecuador at
certain times of the year, you have to be very careful to wade into
the water as stepping on them elicits a poisonous sting which
is very painful and somehow sours the beach vacation. That also goes
for rivers and lagoons in the Amazon where they lay hiding in the
mud. They are the only member of the shark and ray family which
successfully invaded freshwater habitats. Stingrays mostly
feed on fish, crustaceans and mollusks. |
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Sharks are most often found resting on the sea bottom as they
miss a swim bladder to give them buoyancy. Other characteristics is
that they lack true bones but that is more than made up by a strong
cartilaginous structure which provide them also with ever
growing teeth strong enough enough to crush turtle shells. The gills
are not covered by a protective shield (operculum) and are so
visible. |
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The first
fish-like creatures appeared in the Cambrian seas
some 530 million years ago. They were soft-bodied, jawless and
limbless fish similar to today's hagfish and lampreys. From
those fish the first vertebrates (animals with a
true backbone) evolved. So a fish is the common ancestor of all
vertebrate animals (amphibians, reptiles, birds and mammals) to come.
Heavily armored jawless fish known as ostracoderms
evolved along with jawed and limbed fish, the placoderms
(both extinct now). Sharks make their first appearance in
the Ordovician times. Later in the Silurian period the first
bony ancestors of our ray-finned and lobe-finned fish
appeared. In the Devonian period also called the "Age of Fish"
all of them roamed the waters with the ostracoderms being the
most dominant among them. From among the lobe-finned fish
a specie evolved air-breathing lungs from the swim bladder and
enabled it to live for periods on dry land. This one became the
ancestor of all tetrapods as it ventured more and more out the
waters and adapted better to life on dry land until it was
completely independent of the liquid neighborhood. That happened
some 415 million years ago but some other lungfish did
not evolve thus and six species of lungfish are still presently
alive. |
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Fish
are not a true clade but a paraphyletic group.
There are some 28 000
known species which comprises half of all species of
the vertebrates. |
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Petromyzontidae |
40 species
of lampreys |
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Myxinidae |
some 65
species of hagfish |
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Chondrichthyes
(cartilaginous fish) |
360
sharks
500 rays, skates and stingrays |
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Osteichthyes
(bony fish) |
26 000
ray-finned fish
1000 lobe-finned fish |
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Fish are cold-blooded aquatic animals being abundant
in all waters. They are covered with scales and have
two sets of paired fins and several unpaired ones. They
have gills for taking up oxygen dissolved in the water
(although lungfish evolved lungs). Another characteristic is
their swim bladder which gives it buoyancy in the water.
Rays and sharks lack however swim bladders and have to
continuously swim as not to sink to the bottom. Almost
all fish lay eggs into the water where they are fertilized by the
male's sperm and then left to themselves. Some fish however are
known to watch over eggs and fish like the skates give births inside
the female body. |
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