Historically fish have existed for 500 million years and have been idolized as deities in certain religious groups, featured in some of the most popular artwork in history, made the center of countless stories in mythology, become household pets for both the middle and upper class families, gained celebrity status in Hollywood (movies such as Finding Nemo, Finding Dory, Reef and Shark Tale) and attracted millions of viewers at live aquarium shows and exhibits.
Fish can be found swimming throughout all of the worlds oceans and coastal shores from tropical climates near or at the equator to the northern/southern polar hemispheres.
Many species of fish are divided and characterized between the oceanic and freshwater ecosystems.
Unlike marine mammals most fish are cold-blooded which allows their bodies to adapt to various aquatic climate changes with the need for body fat or blubber to keep them warm.
Characteristics
When it comes to fish there are a number of different characteristics that separate fish from other types of marine life.
For example fish do not breathe air the way humans, land animals and cetacean due; instead they use gills to obtain their oxygen.
Gills are respiratory organs that aquatic life forms such as fish use to pull oxygen directly from water instead of having to come to the surface to breathe air the way whales and dolphins do.
Another characteristic that separates fish from marine mammals is the design and function of their spines.
Fish (in most cases) are designed with streamlined bodies that allow them to move quickly through the water and swim forward by moving their body and tails from left to right, while marine mammals such as whales, dolphins and porpoises swim by moving their tail and flukes up and down.
Many species of fish have also developed exoskeletons or scales to aid in protecting them from predators.
The purpose of the exoskeleton is to make it difficult for their predators to penetrate their flesh.
As a species fish can differ drastically in terms of size, speed, diet, function and habitat.
Some examples include comparisons such as the sea-horse which moves at an average speed of 0.5 mph vs the sailfish which can reach speeds of 70 mph.
Another example is the Dwarfgoby fish which measures in at a mere 8-10 mm in length compared to the whale shark which can reach a length of over 50 ft..
The length of time that a fish can survive above water varies significantly from a few minutes up to several weeks depend on the species.
Fish such as the mudskipper are able to navigate on land as well as in the ocean and have the ability to pull oxygen from the air allowing it survive above water for extended periods of time, lasting up to several days.
Other fish are able to survive for weeks in damp environments without direct access to water by entering a state of hibernation until the water returns.
There are also species of fish that can only survive for a few minutes due to the lack of lungs or specialized organs that would be required to assist them with breathing above the waters surface.
In fact while its possible for land and marine mammals to drown below the water its also possible for certain species of fish to suffocate above the surface of the water.
Over many millennium different species of fish have adapted a variety of different mechanisms that are used to extract oxygen from the air.
A couple of these methods include absorbing oxygen directly through the skin and the evolution of accessory breathing organs to help with out-of-water breathing.
The ability to breathe air has proved very useful for a number of amphibians and aquatic animals and allows fish to survive in oxygen depleted waters and murky swamps.
Diet and Senses
In terms of diet some species of small fish can live on a diet primarily containing plants and small aquatic organisms while larger fish may consume smaller fish, squid, crab, larvae and plankton.
Most fish have developed acute senses and are very sensitive to smell and taste.
Many species are also able to see in color and some can detect ultraviolet or polarized light.
Small receptors allow fish to detect subtle changes and vibrations in the current which can alert them of nearby fish as well as dangerous prey.
Studies have also shown that fish do possess pain receptors and experience fear.
When a fish experiences pain several times it can associate a particular situation as the cause of its pain and will react accordingly to the thought of pain being inflicted upon them.
Reproduction
It is currently estimated that over 97% of fish reproduce externally by laying eggs as compared to the majority of marine mammals that carry their offspring internally until birth.
A few species of fish are also known to carry their eggs on or inside their body until the eggs hatch.
Fish that carry their eggs internally are known as being ovoviviparous.
These types of fish carry their young, but provide little to no care from the mother.
There are also a few species of fish that are viviparous and are cared for by their mother during their development stages, similar to the way a mammal cares for its young while it is in the womb.
In these situations the eggs hatch at different times in order to prevent issues with birth or overload the mother since it is unlikely she would survive all of the eggs hatching at once.
Depending on the species a fish may lay anywhere from a few to over a thousand eggs over the course of a year.
By laying a large number of eggs during their reproductive cycle fish are able to maximize their chances of survival and pass their genes on to the next generation.
Because other marine animals consume fish it is important that they lay as many eggs as possible in the hopes that at least some of their offspring will survive and reproduce.
Given the fact that fish lay so many eggs it is impossible for the mother to provide care to each of its children.
How the child develops and hunts for food can vary depending on the species.
In order to survive during the first stages of birth some species of fish are born with a sack that provides them with the nutrients they need to survive until they are able to hunt for their own food.
Other species have been observed consuming other eggs that were laid by the mother and some species are born fully independent and ready to hunt on their own.
Note: Sharks are also considered a species of fish, however they have unique characteristics that separate them from other fish species.
Threats
Over the years fish are becoming more and more at risk with certain types of threats.
Despite there being large populations of some species of fish issues such as overfishing, oil spills, pollution, industrialization, construction, global warming and other environmental changes are causing various species and populations of fish to become endangered, poisoned or forced to migrate to other locations which can cause numerous issues for other marine animals.
Overfishing – In certain areas overfishing is causing some fish populations to become significantly diminished making it more difficult for the marine animals that feed on them to find food and survive.
Continuous overfishing may force certain animal species to migrate away from their local habitat or face possible starvation.
Oil spills – Over the years the growing concern of oil spills and their affects on marine life are continuing to grow.
Areas where oil spills have occurred show large populations of fish either dying or becoming infected which can cause the fish to be born disfigured as well as causing sickness to the marine animals (as well as humans) that feed on the fish as a primary part of their diet to become sick and can lead to death and/or issues with future generations.
Pollution – In addition to oil spills other types of pollution may cause fish to become sick or die and can lead to many of the same complications as those caused by oil spills and other forms of chemical poisoning.
Construction/Industrialization – The construction of dams and bridges along with the increasing number of commercial vehicles inhibiting the ocean can lead to segregation among various fish populations as well as cutting off food supplies to the marine animals that feed on fish.
Global warming/Environmental changes – Global warming and other environmental changes may cause fish and/or other marine animals to migrate away from certain areas leading to food shortages and an unstable ecosystem.
These changes have the potential to cause other marine animals to starve to death due to a lack of available food.
This is especially noticed in areas that are highly commercialized and use specific rivers/waterways to transport goods and/or perform commercial fishing activities (overfishing).
Why fish are important
Fish are extremely important to the oceans ecosystem.
The ability to lay hundreds or thousands of eggs each year allows fish to provide thousands of animals with food on a daily basis.
Without fish many different marine animals would starve to death.
In fact animals such as whales, dolphins, porpoises, polar bears, marine birds and sharks rely heavily on fish to provide them with the nutrients they need to grow into healthy adults so that they can play their part in maintaining the oceans ecosystem and food chain.
In addition to feeding countless animals fish also consume other species of smaller fish and plant life to help boost, stabilize and maintain the oceans animal and plant life balance.
Note: Although animals such as starfish, jellyfish and crayfish carry the word “fish” in their name these marine animals are not considered part of the fish family.