Salmon Life Cycle

Salmon comprises a group of fish species, all of which belong to the family Salmonidae, thus sharing family with trout fish. The main difference between salmon and trout is that the former migrates to another habitat for spawning, while the latter inhabits the same habitat throughout its life cycle. As compared to a typical freshwater or marine fish, a salmon's life cycle is very interesting, which we will discuss in this article.

Salmon Life Cycle Stages

A salmon is anadromous, meaning that this species they spend their entire life in the ocean but migrate to rivers and streams to spawn. In simple terms, they are born and die in freshwater rivers, but remain in the sea till the onset of adult stage. The life cycle of salmon is explained below:

Egg
During fall season, salmon eggs are laid in gravel beds, at the bottom of streams and lakes. Deposited several feet below the water surface, they are protected from exposure to indirect sunlight. The eggs are spherical in shape, slightly translucent with pinkish or reddish coloration. While in the egg stage, the developing organs can be seen easily through the translucent covering. Egg hatching usually takes place within 2 - 3 months after laying.

Newly Hatched Alevin
The water flow and temperature are very crucial for hatching salmon eggs to alevins (1 inch length). They are characterized by presence of abnormally large-sized eyes, attached to a bright orange-colored sac, which is nothing but the nutritive yolk. For nearly 3 - 4 months, the newly hatched alevins reside in the gravel nest, feeding on the yolk that hangs below their body.

Young Salmon Fry
The next stage in the life cycle of salmon is fry. Once the nutritive yolk is absorbed totally, the young salmon fry comes out of the gravel nest. It swims and feeds on small planktons and aquatic plants. Many times, the salmon fry becomes an easy prey to larger fish, insects and birds. In the entire salmon life cycle, the mortality rate is highest, when they are in the egg to fry stage.

Parr Stage
When a salmon fry matures to parr stage, it measures about 6 inch. During this time, vertical markings develop in the body and flanks of salmon. Salmon species like king salmon immediately migrate to the ocean during or after fry stage. While in case of others, the parr may feed and grow in the freshwater streams for approximately 1 - 3 years before starting its journey towards the ocean.

Smolt Stage
In the smolt stage, the developing salmon reaches the estuary, the connecting point where a river meets an ocean. It turns silvery white in color, while losing its vertical stripes. In general, it swims in groups along with others and frequently visits the oceans for feeding purposes. With time, its body gets adjusted to saltwater of the ocean.

Adult Salmon
The body marking of an adult salmon is very distinctive, which differs significantly from one type to another. Based on the species of salmon, the adult may spend anywhere around 3 - 7 years in the ocean, after which it migrates upstream to its birthplace for spawning. The adult salmon stop eating and develop different body colors; males retain bright colors, while females turn darker. The adult female then lays eggs in the spawning site, which again mark the beginning of salmon life cycle.

The average salmon lifespan is seven years. All types of salmon species inhabiting the pacific ocean die immediately after spawning, a behavior referred to as semelparity. Some species, though have the ability to spawn repeated times. Overall, the mortality rate after spawning is very high (40 percent), mainly because the adult spawners cannot spend longer time in freshwater. Thus in a nutshell, a salmon egg hatches in a river, migrates to sea and returns back in the river for spawning.