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Fish
out of water
Many
ancient fish had lung-like organs. These organs evolved into the swim
bladders (which help control buoyancy) of more recent fish species. Some
of these ancient "lunged" fish were the ancestors of modern
amphibians. Many current fish species also spend time out of water:
Rockskippers,
found in Panama, will come out of water to capture prey and escape aquatic
predators. They frequently come out of water for up to 20 minutes at a
time.
Wooly
sculpin, found in the tide pools along the Pacific coast, will leave water
if the oxygen levels get low and can breathe air for 24 hours.
Mudskippers,
found in East Africa and China, often come out of the water and can survive
in air for 3-1/2 days.
While
the ancient amphibious fish may have used their lungs to breathe air, modern
amphibious fish use their gills (and sometimes their skin) to breathe.
These modern species also have eyes adapted to seeing clearly in air, despite
the density differences between air and water.
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Fishy
Facts
Overview.
Generally,
"Fish" are primarily ectothermic (body temperature similar to their
surroundings) vertebrates that live in water and take in oxygen through gills.
There
are two taxonomic classes of fish. Condrichthyes (the sharks and rays)
and Osteichthyes (the bony fish). Bonyfish are further divided into
subclasses. Agnatha (jawless fish like lampreys) and Gnathostomata (jawed
fish like goldfish and bass). There are over 24,600 species of fish -
more than all other vertebrates combined.
Did
you know...?
The
largest freshwater fish found in North America is the Alligator gar, which
may reach 9-1/2 feet and 300 pounds. Alligator gar are found in the
Mississippi River and its tributaries.
The
fastest moving freshwater fish is probably the Northern pike which has been
timed at 20mph over short distances.
Electric
eels (found in rivers in South America) can discharge 400 Volts at 1 Amp, but
jolts of up to 600 volts have been recorded. 650 volts would be enough
to kill a human on contact or stun a horse at a distance of 20 feet.
Sport
fishing
in the United States is an over $100,000,000,000 per year industry and
growing.
In
Illinois, anglers spend $1.6 billion/year and support over 40,000
jobs. Illinois fish hatcheries produce more than 50 million fish per
year for stocking.
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Sea
Lamprey
At
least three types of introduced fish are causing problems in the Great
Lakes. The round goby and ruffe were introduced accidentally from Europe
in the past 10-15 years. Their ranges have spread rapidly and they out compete
many native fish. Interestingly, round gobies are on of the few fish
that can feed on the exotic zebra mussel. Sea lampreys are normally found in
the coastal waters of the Atlantic. these predacious, jawless fish
invaded the Great Lakes through the Welland Canal in 1921. They caused
significant declines in several Great Lakes fish populations, but have since
been successfully controlled through a $10 million per year eradication
program.
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$100,000
Carp
Goldfish
and Koi are among the most popular pet fish worldwide. Koi can be
distinguished from Goldfish by the presence of "barbels" (sensory
extensions) on their upper lip.
Both
Goldfish and Koi have teeth in their throat for grinding up food and
neither have true stomachs. Rather, they have a long, folded intestinal
tract that is perfect for continuous digestion of small amounts of food.
Although
Koi are the national fish of Japan, they did not originate there. The
natural ancestor of Koi is the common carp which is thought to be
originally from Iran. In contrast, the Goldfish shares ancestry with
the Crucian carp from China. Both can trace their captive roots back
to China about 2000 years ago.
Many
Goldfish and Koi shows and contests take place every year all over the
world. Good fish aren't cheap - a breeding-certified, show-quality Koi
may be worth $10,000. A good breeding pair may bring $100,000!
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Fish
and the environment.
Recently,
scientists discovered that migratory fish such as salmon may be
"importing" pollution into new areas. The salmon pick up
pollutants in tainted areas where the toxins enter the food chain when the
salmon breed and die and their eggs and bodies are eaten by other animals.
An
extreme sex bias in some populations of mosquitofish tipped
environmentalists to dangerous pollution released by some paper mills.
Some mosquitofish populations in Florida morphologically seemed to be all
male. It was later discovered that some of these "male" fish
were actually females that had been masculinized by effluent released from
the paper mills. Other effects on different fish species have since
been discovered.
People
releasing pet fish into natural waters may cause unintended and potentially
serious problems. Almost fifty species of exotic fish have established
populations in the U.S., including many cichlid species and goldfish.
These non-native species can disrupt the ecology of the community by competing
with native species and introducing parasites.
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Guppies
in action
Guppies
(Poecilia reticulata) naturally occur in streams in Trinidad, such as
the waterfall picture here. Guppies occur both above and below the
waterfall, but how they (historically) got above such a major obstacles as
this waterfall is unknown.
Guppies
above the waterfall have no major predators. Those below the waterfall
have large fish predators such as mountain mullet. The guppies found
above and below the falls have genetic based differences in behavior, life
history and coloration (e.g., males from low predation streams have larger
and more color spots). Introduction experiments (e.g., placing guppies
from below the falls to above the falls) indicate that these differences can
evolve in only a few years.
In
the fish photo, both males are mature and both are from above (i.e.,
upstream of) the waterfall in the picture. You can tell they are
mature because of the elongated anal fin (the fin before the tail on the
bottom of the fish) that the male uses to insert sperm into the female's
gonadopore.
The
males differ in the number of orange spots that they have. These spots
contain carotenoid pigments which must be obtained from the diet. The
main source of carotenoids for guppies is algae, which grows on rocks in the
stream. It has been argued that carotenoid coloration is an indicator
of male foraging ability and health, which may explain why females prefer
males with larger and more colorful orange spots.
The
size and number of the color spots is highly heritable and controlled by a
small number of genes on the Y chromosome. Wild female guppies
normally lack color spots.
Females
have been shown to like bigger males, males with larger tails, males that
court more intensively, males with less black and more orange coloration,
males with "brighter" orange coloration, males with more
structural (blue) spots and males that have not recently been parasitized (possibly
because the parasite affects orange color). However, usually only one characteristic
is tested at a time which makes it hard to assess their relative
importance. Interestingly, female preference has also been shown to
vary geographically, but currently no one knows why.
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Our
Guppies
The
males are the ones with colorful spots and the elongated anal fin.
Females are larger and usually lack spots.
Guppies
have internal fertilization and females bear live young (notice the babies
in this tank).
Our
guppies are "feeder guppies" from a pet store. These guppies
are approximately the size of the wild guppies. Feeder guppies are
closer in appearance to wild guppies than the fancy guppies sold in pet
stores, but they still often have characteristics that are a result of
artificial selection by breeders (colors, fin shape, etc.) and wouldn't be
found naturally.
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