Fishes Fishes are mainly ectothermic or “cold-blooded” due to

are mainly vertebrates that live and thrive in marine environments. They
typically have an inner skeleton which includes a skull, ribs, and a backbone
except for sharks and rays, which have cartilage. Fishes are mainly ectothermic
or “cold-blooded” due to relying on environmental heat sources. Some exceptions
are tuna, swordfish, and sharks that are “warm- blooded” because they have the
ability to heat their bodies higher than the water’s temperature. Scales
usually surround the skin of most fish and act as reflectors and give the fish
colors. Scales come in a variety of size, shape and color as well as toughness
of the plates.  Fish breathe using gills,
feathery organs full of blood vessels, which help them extract dissolved oxygen
from the water. They accomplish this by taking in water through the mouth and
forcing it out of the gills. As the water passes the thin walls of the gills,
the dissolved oxygen moves into the bloodstream and travels throughout the
fish’s body. The exceptions are lungfish and coelacanth which have paired lungs
and breathe similarly to tetrapods. 

fish move by contracting a pair of muscles found on either side of the backbone,
which travels down the body. The fins, found on either side of the body and
tail, increase the surface area as well as speed. Fish usually have a
streamlined body which decreases friction from the water. Bony fish also have
swim bladders that help them to adjust buoyancy. Fish typically possess highly
developed sense organs; they rely less on their vision and more on their
hearing, taste, and smell because water transmits sounds, disperses chemicals,
and conducts electricity better than air. They can easily detect motion in the
water using a row of scales with sensors commonly known as the lateral line.
They use this lateral line system, which detects currents and vibrations, to
find nearby fish and their food source like prey, as well as navigating through
the waters by detecting electrical charges.1  

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About 70% of the
Earth’s surface is covered in water so fish are found nearly anywhere as long
as they have an ideal environment with sufficient living conditions. Fish can
tolerate different environmental conditions according to their preferred
biological settings but are sensitive to the water having different amounts of
salt, oxygen, types and amount of food, water temperature, hiding areas and
breeding areas.2 There are two types of fishes: saltwater fishes and
freshwater fishes. Freshwater fishes and saltwater fishes control water flow
within their bodies differently to adapt to their environment by using
osmoregulation. Freshwater fishes have body tissues that have a greater salt
content than the water. Their gills help diffuse water and make sure their
bodily fluids remain inside the fish while their kidneys process large amounts
of water. Saltwater fish, on the other hand, lose large amounts of internal
body fluids because the saline water draws water from the body tissues and
leaves through the skin and gills. Because of osmosis the salt water is less
dilute than the internal fluids and rushes in to replace the internal fluids to
form an equilibrium.3 Fish eat a variety of food from plants and
algae to other fish or animals.

Freshwater fish are
found in shallow wetlands, lakes and rivers, where the salinity of water is
less than 0.05 percent.4 Saltwater fish are found from the cold
Antarctic and Arctic ocean to warmer tropical seas. Since prehistoric times,
fish have adapted to living in the water and are found throughout the world’s
oceans from tropical seas with exotic coral reefs to icy polar waters
surrounded by glaciers and ice. Saltwater fish prefer habitats that include
coral reefs. Salt ponds, mangroves, seagrassbeds and the deep sea.4
The saltwater ocean is the main environment that all fish survived in until
geologic events such as earthquakes and volcanic activity created conditions to
isolate groups of fish. Evolutionary adaptations such as time and natural
selection helped create new freshwater fish species. Fish live close to the
oceans surface as well as the darkest depths of the sea. There are many fish
that live in freshwater habitats such as rivers, lakes, and swamps.  Freshwater fish can be characterized as either
a cold water fish or a tropical fish. Examples of tropical freshwater fishes
are: angelfish, cichlids, discus.5 Cold water fish are mostly
goldfish. Examples of cold water saltwater fishes are clown fish, eels,
seahorses, butterfly fish and lionfish. Examples of popular saltwater fish are:
bluefish, cod, flounder, striped bass, sea trout, tarpon, tuna, halibut,
rockfish, sea perch, lingcod, and yellowtail.5 Most ponds, reservoirs
and rivers across North America are freshwater. Common freshwater fish include bluegills,
carp, catfish, crappie, bass, perch, northern pike, trout, and walleye.5
An estuary is where fresh water streams and rivers meet the saltwater from the
ocean. The changes in the salinity will determine which fish can live in the
area. Fish like redfish, sea trout, snook and striped bass. Fish need oxygen as
well to survive which plants in the water help create by the process of
photosynthesis. Water temperature also affects the amount of oxygen the water
can hold seeing as how cold water can hold more oxygen molecules than warm
water as well as different locations. Pollution reduces oxygen in the water by
chemicals trapping the particles and heat reducing the amount of oxygen in the
water. Saltwater fish are found all around North America in waters such as the:
Atlantic Ocean, Pacific Ocean, Arctic Ocean, Caribbean Sea, Gulf of Mexico,
Gulf of Alaska, Beaufort Sea, Hudson Bay, Labrador Sea etc. Freshwater fish in
North America are found mainly wherever fresh water lies in Canada, the United
States and Mexico. Examples would be: Lake Superior, Lake Winnipeg, Lake Erie,
Lake Ontario, Reindeer Lake, Lake Athabasca etc.   

are about 33,000 living fish species according to FishBase, which is greater
than the total of amphibians, reptiles, birds and mammals combined. Around 510
million years back, during the Cambrian era, chordates were the first earliest
organisms that could be considered fish. They had notochords therefore lacking
a true spine, and that allowed them to be more agile that invertebrates. The
Paleozoic era is where fish began to diversify and many of which developed
external armor which aided in defending them from predators. The Silurian era
is when fish began to develop jaws and that made predators more formidable.6

One of the oldest
classes of fishes are Cyclostomata which include lampreys and hagfish, a group
of jawless fish known for their toothed vacuum-like sucking mouth and little teeth.
The class, Chondrichthyes, holds what are known as cartilaginous fish which are
best known as chimeras, sharks, skates and rays.8 They defining
structures are their skeletons which are made out of calcified cartilage and
not bone. All cartilaginous fishes are carnivorous and most species feed on
live prey making this group famous for its largest extent of marine life
predators. There are some species that feed on the remains of dead animals and
still others that are filter feeders. The most diverse of the major groups of
fishes are ray-finned fishes (Actinopterygii), which contain more than 25,000
species such as bowfin, eels, salmon, trout, catfish, piranhas, lanternfish,
cods, anglerfish, tarpon, basses, parrotfish, and many others. 8 Ray-finned
fishes share a set of basic characteristics, including a skeleton made up of
true bone, an upper jaw that consists of two bones and fins that are supported
by a set of bony spines and rays covered with a thin layer of skin. Ray-finned
fishes have diverse and highly adaptable skulls which allow different
mechanisms to occur such as enhancing bite force and jaw protrusion. This
results in a wide range of feeding adaptations and ecological roles for the
actinopterygian fishes.8 Lobe-finned fishes (Sarcopterygii) are a group
of bony fishes with limb-like fins that are fleshy at the base and bones
connected in series that appear and function as limb bones. The living
sarcopterygians include lungfishes (which have both lungs and limb-like fins)
and coealacanths, both are living representatives of diverse fossil groups.8
Lobe-finned fishes hold special interest to evolutionary biologists because members
this group gave rise to the first four-legged land vertebrates (tetrapods).

to scientists, there are approximately 3.5 trillion fish currently living in
the ocean and about 32,000 fish species identified living alongside other sea
creatures.1 The population of fish are constantly fluctuating due to
fishing, predation, reproduction and environmental factors. Humans have
impacted wildlife fishes around North America by overfishing, causing pollution
leading to habitat destruction since industrial times. In the past, humans have
take to hunting fish in the water as a means of survival. Fish are heavily
relied upon as a source of food which humans have caught both as a recreation
and as a means of survival, commonly known as fishing. Fisheries are global
corporations that dedicate their business to catching and selling fish,
offering millions of people income. Fishing from the earliest centuries turned
from a recreational activity and a source of food into a huge worldwide
business, exporting and importing exotic and delicious fish for means of
consumers. The industries have created jobs that help fishers and other people
maintain a source of income. In the future, it would be hard to tell if we have
any fishes left if we are quickly depleting the ocean’s source.

Fishing dates back to at least the
Upper Paleolithic period approximately 40,000 years ago. There is evidence that
a 40,000 year old Tianyuan man from eastern Asia, included freshwater fish in
his diet using isotopic analysis. There have also been fossils of fish bones
and cave paintings found indicating sea food was important for survival in
prehistoric times. The hunter-gatherer lifestyle contained hunting fish as an important
part of early settlements lives. Weapons changed over the course of time too
from using bare hands to nets to harpoons and now to fishing rods.  As the Neolithic culture and technology
flourished, fishing methods became easier and made fishing in dangerous waters
more accessible. Native Americans, from 7500 to 3000 years ago, were known to
fish using gorge hook and line off the Californian coast. The Salt Water Game
Fish of North America figure shows the fish species that were mostly caught to
use as a resource of food.9

is a major threat to edible threat like tuna and cod. Overfishing causes the
population of fish to collapse and forcing the survivors to not being able to
replace those fish that were removed. This is known as commercial extinction
which means the species can no longer sustain a fishery. An example of a
fishery collapse would involve the Paciffic sardine (Sadinops sagax caerulues) typically found off the coast of
California. In the beginning of 1937 to then end of 1968, the catch declined
from 790,000 long tons to 24,000 long tons and after that the fishery was no
longer economically viable to stay afloat.4 Fishes are an important
food resource not only in North America but worldwide and fishing pressure has
caused fish stocks to crash or be at risk. Besides reducing fish stocks,
unsustainable fishing practices can have other negative impacts on the marine
environment. For example, methods of fishing like dredging and trawling can
cause widespread damage to marine habitats and organisms
living on the sea floor. These techniques also tend to capture non-target species, or bycatch, which
are then discarded. 98 Scientists
and conservationists push for protection and warn that many stocks of fish
could be wiped out in fifty years as government and corporations push for
catching more fish.   Technological improvements
improved the style of fishing by gaining an exact measure of navigation and

destruction is another way humans have negatively impacted the fish. Humans
have polluted the water, built dams, removed water for our own uses, farm fish
and introduced exotic species. Marine pollution involves industries dumping
sewage, run-off and chemicals and endangers the lives of fish. They accumulate
the toxic chemicals and produce serious illnesses to humans since we consume
them and are on top of the food chain, a prime example being mercury poisoning.
An example of an endangered fish due to habitat destruction is the North
American freshwater fish, the pallid sturgeon, which lost its home due to
rivers being damaged. Eutrophication also harms fishes and is caused by humans
releasing excess nutrients from fertilizers into streams and rivers. The excess
nutrients promote phytoplankton growth and gives rise to algal blooms which
prevent sunlight from reaching the fish in the water and deprive the water of
its oxygen when decomposition occurs. Acidification of the ocean is also a
human impact because of the excess carbon dioxide we have created, the water
absorbs it and results in seawater becoming too acidic for fishes to live in.10
Introduction of nonnative species causes a problem for native fish in the area
and leads to a competition for resources. Some fish that have caused problem by
being introduced as exotic species include tilapia, carp, brown trout, rainbow trout,
and sea lampreys.

fisherman and sport fishermen exploit coastal marine fish throughout the world
and fish farming is becoming more common. Aquaculture, more known
as fish farming, has been practiced since 3,500 BCE in China and is basically
raising fish commercially in an enclosed body of water. This is different from
a fish hatchery where fish would live and breed as a means of a conservation
effort to save an endangered species. Common important fish that are produced
in fish farming are tilapia, carp, salmon, and catfish. This is an alternative
to wildlife fishing because the demand for fish is increasing and overfishing
is a barrier. As of 2016, more than 50% of seafood is produced by fish farming
with China providing 62% of the world’s most farmed fish.4   

2006 IUCN Red List has named 1,173 fish species that are threatened with
extinction including Atlantic cod, coelancanths, and great white sharks. Freshwater
fish are more threatened because there is a small amount of freshwater
available to them. Different organizations such as the National Oceanic and
Atmospheric Administration and the U.S Wildlife and Fisheries are working to
help save fish in North America and worldwide by getting behind laws such as
the Clean Water Act and the Endangered Species Act and are influencing people
to help save the marine environment. People need fishes as a resource for food
and survival and to observe for scientific research. In the future, the
population growth of humans is expected to increase even more and yet by the
year 2050, it will be impossible to tell if humans will have the luxury of
eating fish if we are depleting the supply already. These organizations should
be better supported and humans need to become aware of the situation at hand
and limit polluting the marine environment as well as overusing the resource
for commercial gain.

a recreational activity, fish have been known to be kept as decorative pets and
are often displayed in diverse sizes shapes and colors in aquariums for our
viewing pleasure. Fishing is also a relaxing activity using fishing rods and
bait where people often throw the fish back into the water. Fish have come to
signify a great deal in religion, such as Christianity by representing Jesus or
Buddhism where the fish symbolizes happiness and “going with the flow”. Humans
enjoy the mass amount of biodiversity that fishes have and often visit
aquariums to see the different shapes and colors of fish. People enjoy fishing
as a hobby and throw the fish back into the water when they’re done. We also
tend to keep fishes as pets. In historical times, fish were symbolic of Christianity
and represented happiness in other religions as well. Humans have made stories
involving fish from books to movies using animation and narratives, such as
Finding Nemo and Jaws.