Round whitefish facts for kids

Quick facts for kids Round whitefish
Scientific classification

The round whitefish (Prosopium cylindraceum) is a type of freshwater fish. You can find it in lakes from Alaska all the way to New England, including the famous Great Lakes.

This fish has an olive-brown back, with shiny silver sides and a light underside. It usually grows to be about 23 to 48 centimeters (9 to 19 inches) long. Round whitefish are "bottom feeders," which means they mostly eat small creatures found on the lakebed. Their diet includes tiny invertebrates like crustaceans, insect larvae, and even fish eggs.

Some other fish, like the white sucker, eat the eggs of the round whitefish. Bigger fish such as Lake trout, northern pike, and burbot hunt and eat adult round whitefish. People sometimes call the round whitefish by other names, like Menominee, pilot fish, frost fish, or round-fish.

Even though it used to be common, the number of round whitefish has been going down over the last 100 years. Because of this, the round whitefish is now protected in some places, like New York. This means you cannot catch or keep them there. In Alaska, people sometimes catch them while fishing for other types of fish, but they are not usually targeted because they live near the bottom.

About the Round Whitefish

The round whitefish belongs to the salmon family. Fish in this group have special features. They have larger scales and smaller mouths. Their teeth are either very weak or they don't have any at all.

The round whitefish has a body shape that looks like a cylinder, which is why its scientific name is cylindraceum. It is mostly silver. Its back has a green tint, and its scales can be brown or bronze with black edges. The lower fins can be amber, and the small adipose fin (a fleshy fin on its back) usually has brown spots.

This fish has many scales: 42 to 46 around its body and 22 to 24 around its tail fin. It also has 83 to 96 scales along its lateral line (a special line of scales that helps fish sense movement). Unlike other whitefish, the round whitefish has only one flap between its nostril openings instead of two.

It can grow up to 50 centimeters (about 20 inches) long. Each year, it usually grows about 55 to 65 millimeters (2 to 2.5 inches). Most of its growth happens in its first five years of life. Round whitefish can live for up to 12 years.

Life Cycle and Reproduction

Round whitefish often travel to and from freshwater tributaries (smaller rivers or streams that flow into a larger one). This is where they go to spawn, which means to lay their eggs.

Spawning spots are usually found in areas with different-sized pebbles. These spots are below the main shoreline currents, about 1 to 1.5 meters (3 to 5 feet) deep. Even at this depth, there is an underwater current. This current helps spread some of the eggs downstream.

Fertilized eggs are small, about 3.10 to 3.25 millimeters (about 0.12 inches) wide. They are kept safe in the spaces between rocks and in the ice crystals on the slushy riverbed.

It's hard to tell the difference between male and female round whitefish just by looking at them. However, during spawning, males develop small, hard bumps called "pearl organs" along their sides. Their fins and belly also change color, becoming yellow-orange or red.

Round whitefish lay their eggs in the fall, usually between early October and late November. This happens when the water temperature is 2.5 degrees Celsius (36.5 degrees Fahrenheit) or colder. They start migrating to their spawning areas in August. Fish that are spawning for the first time might start migrating as early as June.

Most round whitefish spawn for the first time when they are about seven years old. They do not spawn every year, but it is common for them to spawn again the year after their first time. After they become sexually mature and reach the spawning areas, their growth slows down. They grow less each year because they eat less during this time.

Where Round Whitefish Live

Round whitefish live in cold freshwater areas. You can find them in Arctic seas, glacial lakes (lakes formed by glaciers), rivers, and even some brackish waters (water that is a mix of fresh and salt water).

These fish are found across a wide area. They live in the northern waters of North America and the northeastern waters of Asia. They usually live at depths of 55 to over 213 meters (180 to 700+ feet).

In Asia, they are common from the Yenisei River in Siberia to the Kamchatka and the Bering Sea. In North America, you can find them in the Great Lakes (except Lake Erie), parts of the Arctic Ocean, Hudson Bay, waterways in northern Canadian provinces, and throughout Alaska.

Even though they are freshwater fish, round whitefish can be found in parts of the Arctic Ocean where the water is not very salty. This happens because many rivers flow into the Arctic Sea, making the water less salty. This helps explain why they are spread out so widely in northern waters.

What Round Whitefish Eat

Round whitefish are known as "benthivores." This means they mostly eat small creatures that live on the bottom of the water (called benthos) and tiny floating organisms (called plankton).

Their diet also includes creatures like amphipods, gastropods (snails), isopods, and the larvae and pupae of chironomids (a type of fly). They also eat various aquatic insects, such as the spiny water flea.

Round whitefish are "opportunistic feeders." This means they eat whatever food is easiest to find. What they eat can change depending on where they are, what other species are nearby, and the time of year. For example, the types and amounts of prey change with the seasons. Round whitefish are good at adapting to eat whatever is available. This helps them survive when they migrate to and from their spawning sites.

When they return to their usual living areas after spawning and winter, round whitefish eat more chironomids, isopods, and gastropods. During their migration to spawning sites, they mostly eat spiny water fleas, black fly larvae, and other aquatic insects. They do not eat much during spawning, so it's important for them to eat a lot beforehand to store energy.

Round Whitefish and Humans

People do not usually fish for round whitefish for food or for fun. Only a small number of these fish are caught. There are currently no special fisheries (fishing businesses) that focus on catching round whitefish.

Human activities near where round whitefish live can affect them. Studies have looked at how things like mining projects near the shore influence fish populations. A small decrease in round whitefish numbers has been seen around the world. This decline might be due to several reasons. Some studies have noticed less food available for the fish and a decrease in water quality.

Human actions also contribute to global warming. Round whitefish live and spawn in cold waters. If ocean temperatures keep rising because of climate change, these fish could be greatly affected. While the change in round whitefish populations is small compared to some other water animals, it could become a bigger problem if global warming continues. If these problems become serious enough, steps might need to be taken to protect the round whitefish.

See also

In Spanish: Prosopium cylindraceum para niños