Salmon go through a complicated life cycle that involves many changes.
The life cycle starts with an egg laid in a freshwater stream or river. Salmon eggs hatch in the stream and the salmon spend their youth there.
After a year or more, depending on the species, they swim down the river and to the ocean. They spend their adult lives in the ocean.
In summer or autumn, depending on the species, salmon prepare to reproduce. Adult salmon leave the ocean and return to their home stream or river. The journey upstream can last for thousands of kilometres.
When salmon lay and fertilize their eggs, it's called spawning. When the time comes to spawn:
- The female digs depressions in the bottom gravel. These depressions are called redds.
- She lays her eggs. She may lay 2000 to 15 000 eggs over the season.
- While the female releases eggs, the male releases sperm to fertilize the eggs.
- The female sweeps gravel over the eggs with her tail to protect them.
From Egg to Adult
There are several stages in a fish's life before it reaches adulthood.
Eggs are laid in the gravel at the bottom of the river in autumn. They remain there all winter and hatch in spring.
Hatchling salmon are called alevins. They are very small and stay hidden in the gravel in order to avoid being eaten.
At this stage, they can't hunt for food. They get nutrients from their leftover yolk sac, which is attached to their body.
Once they dig out of the gravel and swim into the stream, fish are called fry.
At this stage, they have lost their yolk sac and look more like fish.
Young fry eat microscopic plants and animals, as well as insects, insect larvae and worms. As they grow, they also eat fish eggs and smaller fish.
When salmon are one year old, they are called parrs. They are a small fraction of the size of an adult.
During this stage, the salmon are still in the fresh water of their home stream. Some species stay there for a year or more.
When they're ready to swim to the ocean, salmon are called smolts. Outside, they turn silvery. Inside, their organs prepare for life in salt water.
- a female prepares her nest
Video (40 sec.)
A Dangerous Journey
The upstream journey of salmon to their spawning grounds may last weeks and cover thousands of kilometres—and they don't eat during the journey.
They have to swim, leap and thrash their way against the current, past rapids, rocks, dams and other obstacles.
The salmon also have to avoid humans fishing, especially at the beginning of the trip when the fish are fittest and fattest, and so most desired by people.
Not all of the salmon reach the spawning area at the end of the migration. It depends on the hazards and predators (including humans) that they meet along the way—the more energy the salmon use along the way, the less likely they are to survive.