The salmon life cycle is a complex process that involves a series of stages, typically including egg, alevin, fry, smolt, adult, and spawning. Here’s a breakdown of each stage:
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Egg Stage: Salmon begin their life in freshwater rivers, where adult salmon return to spawn. The female salmon lays thousands of eggs in a gravel nest called a redd, generally during the fall months. The male fertilizes the eggs, and the eggs incubate in the gravel until they develop into alevins.
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Alevin Stage: After about 3 to 6 weeks, depending on water temperature, the fertilized eggs hatch into alevins. Alevins remain in the gravel and carry a yolk sac, which provides them with nutrients. During this stage, they are vulnerable and stay hidden in the gravel to avoid predators.
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Fry Stage: Once the alevins have absorbed their yolk sac, they emerge from the gravel and are known as fry. This stage usually occurs in the spring. Fry begin to swim and feed on small organisms in the water, such as insects and plankton. They continue to grow and develop in freshwater.
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Smolt Stage: As the fry grow, they undergo physiological changes to prepare for life in saltwater. This transformation is known as smoltification, and the fish are now referred to as smolts. Smolts migrate from freshwater rivers to the ocean, usually during spring or early summer. They are now able to osmoregulate, allowing them to survive in saltwater.
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Adult Stage: In the ocean, salmon grow and mature into adults. This stage can last from 1 to 5 years, depending on the species. During their time in the ocean, salmon can travel long distances and can gain substantial weight. They primarily feed on fish, crustaceans, and other marine organisms.
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Spawning Stage: Once they reach maturity, adult salmon return to their natal freshwater rivers to spawn, completing the life cycle. This journey, known as migration, can be perilous and is guided by their incredible sense of smell. Upon reaching their spawning grounds, they reproduce, laying eggs and fertilizing them before dying, although some species can survive to spawn again in subsequent years.
The entire life cycle takes several years to complete, typically around 3 to 7 years, depending on the species of salmon. After spawning, the cycle begins anew with the next generation of eggs.