In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well.
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👉 Hatchling in the context of Viviparous
In animals, viviparity is the development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juvenile that is at least metabolically independent. This is opposed to oviparity, where the embryos develop independently outside the mother in eggs until they are developed enough to break out as hatchlings; and ovoviviparity, where the embryos are developed in eggs that remain carried inside the mother's body until the hatchlings emerge from the mother as juveniles, similar to a live birth.
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Hatchling in the context of Juvenile fish
Fish go through various life stages between fertilization and adulthood. The life of fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.
Hatchling in the context of Salmon run
A salmon run is an annual fish migration event where many salmonid species, which are typically hatched in fresh water and live most of their adult life downstream in the ocean, swim back against the stream to the upper reaches of rivers to spawn on the gravel beds of small creeks. After spawning, most Atlantic salmon and all species of Pacific salmon die, and the salmon life cycle starts over again with the new generation of hatchlings.
Salmon are anadromous, spending their juvenile life in rivers or lakes, and then migrating out to sea where they spend adult lives and gain most of their body mass. When they reach sexual maturity, the adults return to the upstream rivers to reproduce. Usually they return with uncanny precision to the natal river where they were born, and even to the very spawning ground of their birth. It is thought that, when they are in the ocean, they use magnetoreception to locate the general position of their natal river, and once close to the river, that they use their sense of smell to home in on the river entrance and even their natal spawning ground.
Hatchling in the context of Instinctive
Instinct is the inherent inclination of a living organism towards a particular complex behaviour, containing innate (inborn) elements. The simplest example of an instinctive behaviour is a fixed action pattern (FAP), in which a very short to medium length sequence of actions, without variation, are carried out in response to a corresponding clearly defined stimulus.
Any behaviour is instinctive if it is performed without being based upon prior experience (that is, in the absence of learning), and is therefore an expression of innate biological factors. Sea turtles, newly hatched on a beach, will instinctively move toward the ocean. A marsupial climbs into its mother's pouch upon being born. Other examples include animal fighting, animal courtship behaviour, internal escape functions, and the building of nests. Though an instinct is defined by its invariant innate characteristics, details of its performance can be changed by experience; for example, a dog can improve its listening skills by practice.
Hatchling in the context of Sea turtle migration
Sea turtle migration is the long-distance movement of sea turtles (superfamily Chelonioidea), comprising the swimming of adults to their breeding beaches, and also the offshore migration of hatchings. Sea turtle hatchings emerge from underground nests and crawl across the beach towards the sea. They then head offshore to the open sea. The feeding and nesting sites of adult sea turtles may be far apart, requiring some to migrate hundreds or even thousands of kilometres.
Several patterns of adult migration have been identified. Some green sea turtles shuttle between nesting sites and coastal foraging areas. The loggerhead sea turtle uses a series of foraging sites. Others such as the leatherback sea turtle and olive ridley sea turtle do not keep to one coastal foraging site, but forage in different areas in the open sea. Although the leatherbacks seem to forage randomly, drifting passively with the currents, they still return to specific sites to breed. The ability of adult sea turtles to travel to precise locations has led biologists to wonder about their navigational mechanisms. Some have suggested that turtles might use the Earth's magnetic field to fix their position. There is evidence for this ability in juvenile green sea turtles.