Three-spined stickleback

The three-spined stickleback is a small fish.

It lives in salt water and fresh water. It likes slow water with plants.

This fish has sharp spines on its back. The spines lock in place. This makes it hard to swallow.

During breeding time, the males look different. Their eyes turn blue. Their throats turn bright red. They also build nests for their eggs.

The three-spined stickleback is a small fish.

It lives in many places. You can find it in salt water and fresh water. It likes slow water with plants.

This fish has sharp spines on its back. Most have three spines. These spines can lock in place. This makes the fish hard to swallow.

Instead of scales, it has bony plates. Some fish have many plates. Others have very few or none at all.

Sticklebacks change a lot depending on where they live. Some live in the sea and return to fresh water to breed. These are called anadromous fish. Others live in lakes all year. These fish often have less armor. In some lakes, fish live in different spots. Some eat near the surface. Others eat on the lake bed. These groups can become different species through ecological speciation. This is when living in different spots makes them change.

Scientists study them to learn how life changes over time.

The three-spined stickleback is a small fish that scientists love to study.

These fish live in many different waters across the Northern Hemisphere. They can be found in salty oceans or fresh lakes and rivers. Many groups are anadromous, which means they live in the sea but swim to fresh water to breed.

They like slow water with plants to hide in. This fish is a great way for researchers to learn how living things change over time. Because they are easy to find and keep in tanks, they help us understand the natural world.

This fish has a very clever way to stay safe from predators.

It has sharp spines on its back that can lock in an upright position. This makes the fish very hard for a larger animal to swallow. Instead of having scales like many other fish, the stickleback has bony plates. The number of these plates changes depending on where the fish lives.

Fish in the ocean often have many plates for armor. However, fish living in fresh water might have very few or even none at all.

Sticklebacks have been around for a very long time.

Scientists found fossils that look almost exactly like the fish we see today. These fossils come from the Monterey Formation in California and are over 10 million years old. This tells us the species has stayed mostly the same for a huge amount of time. There was also a related fossil called Gasterosteus doryssus from the Miocene period. That older fish lived in fresh water in Nevada and also changed very quickly. This shows that the stickleback family has always been good at adapting.

These fish live in many places from Alaska to Japan.

In North America, they live from California all the way to the Bering Straits. They can be found in ponds, marshes, and even quiet rivers. Some sticklebacks are very small, usually growing between 6 and 10 centimeters long. During the breeding season, males change color to look special. Their eyes might turn blue and their throats can turn bright red. This helps them during their elaborate breeding time.

Watching sticklebacks helps us see how new species are made.

In some lakes, one group of fish eats near the surface while another eats on the bottom. These groups are called the limnetic and benthic forms. Because they live in different spots, they often stop breeding with each other. This is called ecological speciation, where the environment drives the change.

It is like how two groups of friends might start having different hobbies because they hang out in different places. Eventually, those small changes can turn them into entirely different types of fish.

The three-spined stickleback, known scientifically as Gasterosteus aculeatus, is a small fish found throughout the Northern Hemisphere.

This species is a vital subject for scientists studying evolution and population genetics. It is famous for its morphological variation, which means its physical shape and structure can change significantly between different groups. Many populations are anadromous, meaning they live in saltwater but move to freshwater or brackish water to breed. Because they are easy to find in nature and easy to keep in aquaria, they provide a perfect way to observe how living things adapt to new environments.

To protect themselves from predators, the stickleback has developed a unique physical defense system.

The fish possesses sharp spines on its back, located in front of the dorsal fin. While most have three spines, some individuals may have only two or four. These spines can be locked in an upright position, making the fish very difficult for a predator to swallow. Instead of traditional scales, the stickleback uses bony plates for armor on its back, flanks, and belly. The number of these lateral plates varies greatly depending on the habitat. Marine populations often have many plates, while some freshwater populations may lack them entirely.

Sticklebacks have a long and impressive history in the fossil record.

The species appears to be quite old and has remained morphologically unchanged for more than 10 million years. Scientists have found fossils in the Monterey Formation of California that look almost identical to modern sticklebacks. These specimens come from marine deposits, suggesting the fish has had a marine or anadromous lifestyle for a very long time. A related fossil species, Gasterosteus doryssus, lived in the Miocene-aged freshwater deposits of Nevada. This relative also showed a tendency for rapid evolution, suggesting that the ability to change quickly is a long-standing trait of the Gasterosteus lineage.

These fish inhabit a wide variety of environments across the globe.

In North America, they range from southern California to the Aleutian Islands and the western shore of Hudson Bay. In Europe, they live between 35 and 70°N, and in Asia, they stretch from Japan to the Bering Straits. They prefer slow-flowing water with emerging vegetation, such as ponds, marshes, lakes, and quiet rivers. While they can reach larger sizes, most adults are commonly between 6 and 10 centimeters long. During the breeding season, males undergo a dramatic color change. Their eyes may turn blue, and their throats and bellies can turn bright red to attract mates.

One of the most fascinating aspects of the stickleback is how they divide into different ecological niches.

In many lakes, two distinct forms emerge: the limnetic and the benthic. Limnetic fish live in deep, steep-sided lakes and feed on plankton near the surface. They often have large eyes, slim bodies, and upturned jaws. Benthic fish live in shallow lakes and feed on the lake bed. These fish are typically longer with heavier bodies, smaller eyes, and horizontal jaws. Because these two groups occupy different roles, they often stop interbreeding, a process known as ecological speciation.

This process of ecological speciation can happen very quickly.

In Loberg Lake, Alaska, researchers observed rapid changes after a chemical program removed freshwater populations in 1982. When oceanic sticklebacks recolonized the lake, the population changed significantly in just 12 years. By 1990, the frequency of the oceanic form dropped from 100% to 11%, while a variety with fewer armor plates increased to 75%. This shows how genetic variations can allow a population to adapt to new conditions, like moving from salt to fresh water, in a very short amount of time.

While the three-spined stickleback is generally considered a species of "least concern," some specific populations are in danger.

In British Columbia, certain species pairs of limnetic and benthic sticklebacks are listed as Endangered under the Canadian Species at Risk Act. These populations are vulnerable because they can be destroyed by the introduction of new predators, such as catfish. When these unique environments are disturbed, the specialized fish that evolved there may be lost forever. Studying these fish helps us understand the delicate balance of how species form and how they respond to a changing world.