The necton It is the group of organisms that live in the water column and that have autonomous movement. That is, they are organisms capable of swimming and opposing water currents. Necton an ecological and non-taxonomic term.
This term applies to both marine and freshwater organisms. Animals are the only organisms capable of active swimming. The main group of animals that make up nekton is that of fish.
Other taxonomic groups that also have representatives in the nekton include mollusks, crustaceans, reptiles, birds, and mammals. The nekton group is quite diverse in terms of the size of its members. Some species can measure from 5 cm, being the largest members up to 50 m in length.
For some nekton studies, such as population density studies, the same capture methods are used as for commercial fisheries..
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Due to the need to move in an environment as dense as water, they present morphological and / or physiological adaptations that facilitate their swimming. Many have a hydrodynamic fusiform or pisciform body.
Fish, for example, have a gas bladder, or swim bladder. This structure helps them stay in the water column with a lower energy cost..
Other adaptations include the secretion of mucous substances that coat the body and reduce friction, or the accumulation of fat reserves, less dense than water..
In most cases, the locomotive appendages are shaped like oars, like the fins of fish or cetaceans..
Virtually all members of the nekton feed on other animals. All have special adaptations to defend themselves or attack their prey. The musculature is generally well developed to ensure agile and precise movements.
Virtually all members of the nekton are carnivores. Some are plankton eaters, that is, they feed on plankton. Others can feed on benthic organisms. Most, however, feed on other members of the nekton.
Many small fish, such as herring and sardines, are among the planktonphagous organisms. However, other larger species also feed on plankton, mainly krill, a species of crustacean of the order Euphausiacea.
Among the species that feed on krill is the largest known fish, the whale shark. There is also the baleen whale. Penguins and seals also eat krill. Some species of sea turtles feed on jellyfish, other members of plankton.
Among the nekton organisms that feed on benthos are parrotfish, which feed by scraping the surface of corals. Other nektonic fish can feed on sea urchins, crabs, polychaetes, and other benthic species.
Some sea turtles feed on sea grasses, others can eat mollusks and crabs.
The representatives of the nekton that feed on other nektonic organisms are represented by fish such as tunas, barracudas or sharks. Killer whales feed on seals, fish and penguins.
Penguins, apart from krill, also include small fish in their diet. Herring whales feed on sardines and herring.
They are organisms that spend their entire lives as members of the nekton. Examples: tuna, salmon and cetaceans.
They are the organisms that live in both aquatic and terrestrial environments. Examples: penguins, alligators, and turtles.
They live only part of their life cycle in nekton. Examples: the larvae of amphibians and some insects.
The mollusks representing the nekton belong to the cephalopod class. Among these are squid, octopus, nautilus and argonauts. Nautiluses and Argonauts are cephalopods with external cocha.
As an adaptation to nectonic life, nautiluses and Argonauts have their shells internally divided by partitions. Each septum has a hole through which a cord of tissue called a sifunculus passes..
Animals live only in the outermost chamber. In the rest of the chambers they regulate, by means of the sifunculus, the amount of water and gases present. In this way they can regulate their buoyancy.
The nautilus' buoyancy control mechanism inspired the construction of the submarines.
Crustaceans have numerous representatives in nekton. Among these are several species of shrimp, for example those of the Sergestidae family. Miscidaceans are other crustaceans of the nekton.
Another example is the Anostracos, such as the Artemia, which is important, as it is the main food used in aquaculture.
There are some species of freshwater Anostracos.
Most of the insects that are representatives of nekton are only representatives during their larval stage. They are part of the meronecton. An example of this are the larvae of dragonflies. Only a few species of insects are aquatic during their adult stage, such as scuba beetles.
Most of the fish are nektonic. They are important from an economic point of view, since the fisheries of many nations are based on nectonic species. Examples of nectonic fish are salmon, tuna, sardines, sharks, among others..
Some fish spend their entire lives in the sea or in the river, others carry out reproductive migrations, one or more times in their life, between the river and the sea..
Amphibian larvae develop in aquatic environments. Axolotls, for their part, remain in the water all their lives. These organisms are actually neotenic states of salamanders.
Neoteny is a phenomenon characterized by the fact that the organisms that possess it reach sexual maturity preserving juvenile or larval characters..
Nekton reptiles are represented by turtles, alligators, crocodiles, and sea snakes. Among sea turtles, females spend most of their lives in the water. They only come out of it to build their nests and lay their eggs..
The males, once they hatch from the eggs and emerge from the nests, enter the sea and never return to land.
The main representatives of nectonic birds are penguins, which have undergone important adaptations for aquatic life. These include a hydrodynamic body and modified wings for swimming.
They are represented mainly by cetaceans, pinnipeds and sirenids. Cetaceans and sirenids have both freshwater and marine species.
Freshwater cetaceans are known as dolphins or freshwater dolphins. Those of salt water are whales, killer whales, dolphins, narwhals, among others.
The freshwater sirenians, for their part, are manatees, although they can also live in the sea. The marine sirenians are the dugongs.
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