Salmonidae

Many fish live in cold water.

These fish include salmon and trout. They have long bodies and sharp teeth. They use their teeth to eat small fish and bugs.

Some fish live in rivers. Others swim in the big sea. They move from rivers to the sea to grow.

This move helps bring food to the land. These fish are very important to our world.

Salmonids are a big family of fish. This group includes salmon, trout, and char. There are over 200 different species.

Most salmonids live in cold water. They like the cool parts of the Northern Hemisphere. These fish have long, slender bodies. They also have sharp teeth to eat small fish and bugs.

Many salmonids follow a special way of life. They are anadromous, which means they move between fresh and salt water. They start their lives in small, shallow streams. They grow up in rivers or lakes. When they are adults, they swim to the big sea.

Later, they return to the streams to lay eggs. This move helps bring food to the land.

Salmonids are very old. Scientists found fossils from a long time ago. One old fossil is called Eosalmo driftwoodensis.

These fish have changed a lot over millions of years. They are still a very important part of our world.

Salmonids are a large family of fish found in cool waters. This group includes salmon, trout, char, and graylings. There are about 220 different species in this family.

They live in the Northern Hemisphere in subarctic and temperate areas. Most of these fish have slender bodies and rounded scales. They also have a single row of sharp teeth.

They are middle-level predators that eat insects and smaller fish. Many are also considered keystone organisms. This means they are very important to their environment. They move energy from the ocean to the land when they migrate.

Many salmonids follow a special way of life called anadromous. This describes fish that move between salt water and fresh water. They begin their lives in shallow gravel beds in small streams. The young fish spend their growing years in rivers or lakes. When they are adults, they migrate to the sea or estuaries. Some species are euryhaline, so they can handle different types of water. These fish eventually return to the upper streams to spawn. Other salmonids are potamodromous and only move between lakes and rivers.

Scientists have studied these fish for a very long time. The group is divided into three main subfamilies. These are Coregoninae, which are whitefishes, and Thymallinae, which are graylings. The third is Salmoninae, which includes salmon and trout.

The Atlantic salmon is the most famous member. Its name even helped give the family its name. Researchers use genetics to understand how these groups are related. This helps them see how the fish changed over time.

Fossils show that salmonids have been around for millions of years. One very old fossil is called Eosalmo driftwoodensis. It was found in British Columbia and is considered an archaic salmonid.

In 2025, scientists described a new fossil called Sivulliusalmo alaskensis. This fossil was found in the Prince Creek Formation of Alaska. It lived during the Cretaceous period. This suggests that these fish have always liked cool, northern waters. Other fossils like Oncorhynchus appeared in Idaho about 7 million years ago. This shows that different types of trout had already split apart.

Salmonids are special because of something called genome duplication. This happened to their ancestors about 88 million years ago. This event doubled their genetic material.

Even today, some fish like the rainbow trout show signs of this. They are partially tetraploid, which means they still carry parts of that extra DNA. This extra information might help them adapt to the world. Many species changed and grew during the last ice ages. These periods of climate change helped different types of salmonids form. They continue to be amazing survivors in our world.

Salmonidae is a diverse family of ray-finned fish. It includes over 200 species across 11 different genera. These fish are collectively known as salmonids. They are mostly coldwater predators found in the Northern Hemisphere. This includes subarctic and cool temperate waters. The family includes salmon, trout, char, graylings, and whitefishes. It also contains taimens and lenoks.

They are important middle-level predators in the food chain. This means they eat smaller fish, insects, and crustaceans. They are also eaten by larger predators. Because they move nutrients between environments, they are often called keystone organisms.

Salmonids follow complex life cycles involving migration. Many species are anadromous, meaning they move between salt and fresh water. They begin their lives in shallow gravel beds in freshwater streams. The juveniles grow in rivers, creeks, or small lakes. Upon reaching maturity, they migrate downstream to larger waterbodies like the sea. Many are euryhaline, which means they can tolerate different salt levels. This allows them to enter brackish estuaries or the open ocean.

Other species are potamodromous. These fish migrate only between different freshwater habitats like lakes and rivers.

Taxonomically, the family is divided into three main subfamilies. The first is Coregoninae, which includes freshwater whitefishes. This group contains genera like Coregonus and Prosopium. The second subfamily is Thymallinae, which contains the graylings. The third and largest is Salmoninae. This subfamily includes salmon, trout, char, taimens, and lenoks.

Within Salmoninae, there are different tribes. The tribe Salmonini includes the genus Salmo, which contains Atlantic salmon. The tribe Oncorhynchini includes the genus Oncorhynchus, which contains Pacific salmon and trout.

Fossil evidence reveals a long evolutionary history for these fish. The order Salmoniformes first appeared during the Late Cretaceous period. For a long time, scientists thought the earliest salmonid was Eosalmo driftwoodensis. This fossil was found in British Columbia and represents an archaic stage of evolution.

However, in 2025, a new discovery changed this timeline. Scientists described Sivulliusalmo alaskensis from the Prince Creek Formation in Alaska. This fossil dates back to the Cretaceous period. Its presence in northern habitats suggests that salmonids have always preferred cool waters.

Genetic studies provide deep insight into how salmonids evolved. About 88 million years ago, the ancestors of salmonids underwent a whole-genome duplication. This event turned a diploid ancestor into a tetraploid one. A tetraploid organism has four sets of chromosomes instead of two. This is a massive change to the genetic blueprint.

Modern salmonids show evidence of partial tetraploidy. This means they have worked to return to a diploid state through natural selection. In rainbow trout, about half of the duplicated protein-coding genes have been deleted. However, all apparent miRNA sequences still show full duplication. This genetic complexity may help regulate how their genomes function.

Climate change has also played a major role in their diversity. While genome duplication was once thought to be the main cause of variation, newer studies suggest otherwise. Molecular clock analyses show that much of the speciation occurred during the last ice ages. These periods of intense climate change drove the evolution of many species. Specifically, salmonids that developed an anadromous lifestyle saw high rates of speciation. The changing environment forced these fish to adapt to new ways of moving through water.

Salmonids are closely related to other fish groups. They belong to the superorder Protacanthopterygii. This group also includes the orders Esociformes, which contains pikes, and Osmeriformes. Recent studies have affirmed the relationship between Salmonoidei and Esocoidei. This means pikes and salmonids are part of a shared evolutionary lineage. This connection helps scientists understand the broader history of bony fishes. The study of salmonid evolution continues to grow as new fossils and genetic tools become available.