1. Journey to Spawning Grounds:
* Salmon are anadromous fish, meaning they live in saltwater but migrate to freshwater to spawn.
* When it's time to reproduce, salmon leave their saltwater habitat and travel upstream to their natal (birth) rivers. This journey can be thousands of miles long and extremely challenging.
2. Physical Transformations:
* During the journey, salmon undergo physical transformations. Their bodies adapt to the freshwater environment, and they develop breeding coloration: males become more colorful, often with a hooked jaw, while females become more robust.
3. Finding a Suitable Site:
* Once they reach their spawning grounds, salmon search for suitable locations – usually gravel beds with strong currents.
* The female salmon will use her tail to dig a depression in the gravel bed called a redd.
4. Spawning:
* The female salmon lays her eggs in the redd, while the male releases his milt (sperm) over them.
* The eggs are fertilized externally, and the male may guard the redd from predators or other males.
5. Incubation and Hatching:
* Eggs incubate in the gravel for several weeks or months depending on the species and water temperature.
* During this time, the developing embryos obtain nutrients from the yolk sac.
* Once the embryos have fully developed, they hatch into alevins (small salmon with a yolk sac attached).
6. Alevins and Fry:
* Alevins remain in the gravel bed, absorbing nutrients from the yolk sac until they are ready to swim freely.
* After the yolk sac is absorbed, the alevins become fry – small, free-swimming salmon.
7. Life Cycle Continues:
* Fry spend several months in freshwater, developing and feeding before migrating to saltwater.
* In the ocean, salmon grow rapidly and mature.
* When they are sexually mature, they return to their natal rivers to repeat the spawning cycle.
Interesting Facts:
* Some salmon species only spawn once in their lifetime and die shortly after.
* Salmon have a strong instinct to return to their natal river, even though they may have never been there before.
* The journey back to the spawning grounds is extremely strenuous, and many salmon die before they can reproduce.
The life cycle of salmon is a testament to their resilience and incredible adaptations for survival. They are vital to the health of freshwater and marine ecosystems, and their conservation is crucial for the balance of our planet.