Nature, Uncategorized

Why do Fish Swim Upstream?

Each year, thousands of salmon swim upstream to spawn. They follow a familiar scent that leads them to where the cycle of life begins (location of their birth). By laying eggs in shallow waters, they provide shelter and ensure they are not washed away by heavy currents.

The battle to go upstream wears the fish and some of them die in this quest because it takes every ounce of energy for the fish to make it.

The latest statistics suggest that adults die within a week. However, their decaying bodies create a favorable environment for the growing embryos.

About 5-10% of the fish survive back to the ocean. Younger fish find it hard to survive in the ocean. But the large food sources make the fish prepare for this epic journey. The young fish have yolks on their throats, so after some time, they feed on insects.

This makes them gentler when going upstream. You’ll often see the fish feeding on larger insects after exploring the larger bodies of water.

How fish swim upstream

The fish tilts the body such that the vortices create a suction force to propel the fish forward. Also, the streamlined body makes the fish swim against the current (under the right conditions). Anyone who has ever tried to grab this fish knows the head and tail can move independently.

Which fish swims upstream?

Salmon is well known to swim upstream. While there are many species of salmon that swim upstream, the most targeted ones by fishermen are:

King salmon

It’s easily identified by the large size and features some dark-green backs. Their tails and upper body have some black spots. What makes the king salmon unique is that it can weigh up to 55 pounds.

Coho salmon

It looks identical to the king salmon and weighs up to 15 pounds. The easiest way to tell the difference between the two is by looking at their mouths. The Coho salmon features white jaws and white gums.

Pink Salmon

This species is also known to swim upstream and can weigh up to 5 pounds. Each year, you’ll find many pink salmons swimming upriver in the Pacific Northwest. And due to the physical changes the fish go through, some people call it the humpback salmon. It’s believed that the males turn to bright pink and grow humps before dying. Note: no pink salmon survives after swimming upstream.

Sockeye salmon

It’s smaller than king salmon and can grow up to 10 pounds. It’s one of the most prevalent species behind the chum and pink salmon. This fish lives in the same environment as the other species.

Chum salmon

Chum is one of the least targeted species of salmon by fishermen. The reason why most fishermen avoid this fish is they taste bad after the spawn. The average Chum salmon can grow up to 15 pounds.

Most adults die within a week after swimming upstream, leaving the young to fetch for themselves.

Other fish species that swim upstream are:

ALOSA (American Shad)

Alosa is native to North America. It’s known to swim in the Schuylkill River and feeds at Valley Forge. This silvery fish features some black spots and a green band. Also, it has a short belly, not to mention an adult can weigh up to 20 inches. Alosa is known to migrate upstream and tends to re-spawn multiple times.

Spotted Seatrout

This fish belongs to the trout to the family and bites, unlike other fish. It’s long-bodied and has black specs on the back.

Spotted Seatrout is native to East Coast and averages up to 6 pounds. It tends to hibernate in cold temperatures, but the warm temperatures trigger spawning. And this usually happens between May and September – they follow the connecting rivers.


HILSA is native to Eastern Countries and is a major supply of food in India. It also inhibits the Arabian Sea (the Bay of Senegal) and can grow up to 23 inches. HILSA migrates upstream twice a year, especially during the monsoon season.

Sturgeon (ACIPENSER)

The Sturgeon is known to swim upstream and come in different sizes. The young fish can weigh 25 pounds, while adults can weigh up to 2500 pounds.

How can you identify the Sturgeon? It features bony scutes on the head and the upper part of the body. These plates also run on the horizontal section of the body.

The tail resembles that of a shark and tends to have a cartilages skeleton. What’s more, it comes with a heterocercal tail – helps the fish to propel seamlessly in water.

Most of the species live in the northern hemisphere, with a few species living in species. This fish likes to migrate from the oceanic waters.

When fish swim upstream

Salmon tend to swim upstream in late autumn. This can also happen any time the water temperature proves adequate. If the cold stream water for spawning turns up in autumn, they have to adapt to the changes and swim upstream. Sometimes, spawning can happen at unpredictable times of the year and this is the best time to start their journey home.

How long it takes

It can take a couple of weeks for salmon to flow upstream to where they spawn. But the fish has to wait for the big rain in September and October when the rivers are high.

Sometimes, the distance can be more than two miles. So, waiting for the big rains can help the fish swim past obstacles on the way. If there’re manmade dams on the way, you’ll see throughways or ladders that allow the fish to go over them.

 But the journey will depend on water clarity and the place where the water flows.

The above fish species are known to swim upstream. However, salmons have a fighting spirit that makes them fun to catch when migrating. They try to swim upstream for spawning and the benefit of future generations. This pattern repeats itself year after year.