Rainbow trout

The rainbow trout is a pretty fish.

It likes to live in cold water. Most of them live in rivers.

You can see a red stripe on its side. This stripe is very bright on males. Some fish live in the big ocean. These ocean fish are called steelhead. They swim back to rivers to lay eggs.

The mother fish digs a nest in the gravel. She hides her eggs in the stones. The eggs hatch in a few weeks. Then the tiny fish start to eat.

The rainbow trout is a beautiful fish.

It lives in cold water. Most live in rivers in North America and Asia.

You can see a red stripe on its side. This stripe is brightest on males during breeding season. Adult fish in rivers are often olive green with black spots.

Some fish live in the ocean. We call these sea-run fish steelhead. They live in the salt water for two or three years. Then they swim back to fresh water to spawn. Spawning is when fish lay eggs to make new babies.

A female trout makes a nest in river gravel. She turns on her side and beats her tail. This clears a spot called a redd. She lays eggs in the gravel. A male then swims by to fertilize them. The eggs hatch in four to seven weeks. The tiny new fish are called alevin. They have a small sac of food on them. In two weeks, they eat the sac. Then they start to eat tiny water bugs. As they grow, they get dark bars on their sides. These young fish are called parr.

The rainbow trout is a very special kind of fish.

These fish live in cold waters. Most of them live in rivers that flow into the Pacific Ocean. This includes parts of North America and Asia.

Some trout are even called steelhead. These are fish that live in the ocean for a few years. Then they swim back to fresh water to have babies.

There is a neat way these fish grow and make families.

First, a female trout finds a spot with fine gravel. She turns on her side and beats her tail to clear a nest. This nest is called a redd. She lays her eggs inside the gravel. Then a male swims by to fertilize them. The eggs hatch in four to seven weeks. The tiny babies are called alevin. They carry a small sac of food for two weeks.

People have studied these fish for a long time.

A German scientist named Johann Julius Walbaum named the species in 1792. He found his specimens on the Kamchatka Peninsula in Siberia. He used a local name for the fish to name it. Later, a Scottish naturalist named Sir John Richardson named a specimen in 1836. He did this to honor a surgeon named Meredith Gairdner. In 1855, William P. Gibbons gave them the name rainbow. Scientists later moved them into a group called Oncorhynchus. This group includes Pacific salmon.

Rainbow trout come in many different sizes and colors.

In rivers, adults are often olive green with black spots. They have a bright red stripe along their sides. This stripe is very vivid on males during breeding time. In lakes or the ocean, they look more silvery.

Freshwater fish usually stay between 10 and 12 inches long. However, lake fish or steelhead can grow much larger. Some special types have different colors too. For example, the golden rainbow trout is mostly yellow. These were first found in a West Virginia hatchery in 1955.

These fish are found almost everywhere on Earth.

Humans have moved them to 45 different countries. They are on every continent except Antarctica. Sometimes, people move them to new places for sport fishing. This helped create fishing spots in the Great Lakes.

But moving them can also be a hard job for nature. They can crowd out native fish or spread diseases. This is why some groups are protected by laws. We must be careful to keep their homes healthy.

The rainbow trout, known scientifically as Oncorhynchus mykiss, is a remarkable species of fish.

These fish are native to the cold-water tributaries of the Pacific Ocean. This includes regions in both North America and Asia. They are highly valued for both food and sport fishing. Because they are so adaptable, they are found in many different environments. They can live in small rivers, large lakes, or even the salty ocean.

One fascinating aspect of this species is its life cycle. Some trout are anadromous, which means they are sea-run fish.

These specific fish are commonly called steelhead. They spend two to three years living in the ocean to grow large. Eventually, they return to freshwater streams to spawn, or lay eggs. Unlike some Pacific salmon, steelhead are iteroparous. This means they can spawn several times throughout their lives. However, fewer than 10 percent of native spawning adults survive between these trips.

The process of reproduction begins in the spring.

Spawning usually happens between January and June in the Northern Hemisphere. The water temperature must reach at least 4 degrees Celsius for this to occur. A female trout finds a bed of fine gravel in a shallow river. She clears a nest, called a redd, by beating her tail against the gravel. She then lays between 2,000 and 3,000 eggs per kilogram of her body weight. As the eggs are released, a male deposits milt to fertilize them. The female covers the eggs with gravel to protect them.

After the eggs hatch in four to seven weeks, the young fish enter new stages. The newly hatched trout are called sac fry or alevin. For about two weeks, they rely on a yolk sac for food. Once the sac is consumed, they become fry and eat zooplankton. As they grow, they develop dark vertical bars called parr marks. These small juveniles are sometimes called fingerlings because they are roughly the size of a human finger.

The maximum recorded lifespan for a rainbow trout is 11 years.

Rainbow trout display a wide variety of colors and sizes.

Freshwater adults are often olive or blue-green with heavy black spots. They feature a bright reddish stripe along their lateral line. This stripe is most vivid in males during the breeding season. In contrast, lake-dwelling and anadromous forms are often more silvery.

Size also varies greatly depending on the habitat. Freshwater river trout average 25 to 30 centimeters. However, lake or ocean forms can reach much larger sizes. Some unique varieties exist, such as the golden rainbow trout. These yellow fish were first seen in a West Virginia hatchery in 1955.

The history of naming this fish is quite complex.

In 1792, the German naturalist Johann Julius Walbaum first named the species. He used specimens from the Kamchatka Peninsula in Siberia. He based his name, mykiss, on the local name mykizha. In 1836, Sir John Richardson named a specimen to honor surgeon Meredith Gairdner. Later, in 1855, William P. Gibbons called them rainbow trout. In 1989, scientists realized these trout were genetically closer to Pacific salmon. This led to their placement in the genus Oncorhynchus.

While rainbow trout are useful for sport, they can also be invasive.

They have been introduced to at least 45 countries across every continent except Antarctica. In places like Australia and South America, they can harm native species. They may prey on local fish or spread diseases like whirling disease. They can also out-compete native fish for food and space. Because of these impacts, the rainbow trout is listed among the top 100 globally invasive species. Some specific populations are even protected under the Endangered Species Act.