Ruffe facts for kids
The Eurasian ruffe (Gymnocephalus cernua) is a freshwater fish. It is also called ruffe or pope. This fish lives in cool parts of Europe and northern Asia. It has also been brought to the Great Lakes in North America. There, it has become an invasive species. This means it reproduces quickly and can cause problems for other fish.
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What Does the Ruffe Look Like?
The ruffe has colors similar to a walleye fish. Its back is olive-brown to golden-brown. Its sides are lighter, and its belly is yellowish-white.
This fish can grow up to 25 cm (9.8 in) long. But it is usually about half that size. Even though it is small, the ruffe is a very aggressive fish.
The ruffe has a large, spiny dorsal fin on its back. This fin likely tastes bad to animals that try to eat it. It has two fins on top. The front fin has hard, sharp spines. The back fin has soft spines called rays. You can easily spot a ruffe by its large, single dorsal fin and its mouth, which points slightly downwards.
Where Do Ruffe Live?
Ruffe are found in many places naturally. They live in the areas around the Caspian, Black, Aral, Baltic, and North Seas. You can also find them in Great Britain and parts of Scandinavia. They live in some areas of the Arctic Ocean basin, going east to the Kolyma River.
People have also brought ruffe to other places. These include parts of Western Europe, like France and northern Italy. They are also in Greece and the Great Lakes in North America.
What Do Ruffe Eat?
In Europe and Asia, ruffe mainly eat small creatures that live at the bottom of the water. These include chironomids, which are tiny aquatic bugs and their larvae. These foods are found in the benthic zone, which is the bottom area of a body of water.
When ruffe were brought to the Great Lakes, they kept the same diet. They continue to eat these small bottom-dwelling creatures.
How Do Ruffe Reproduce?
Ruffe can reproduce very quickly. A ruffe usually becomes old enough to have babies in two to three years. However, if a ruffe lives in warmer water, it can reproduce in its first year of life.
A single female ruffe can lay a lot of eggs. She might lay between 130,000 and 200,000 eggs each year! Ruffe prefer deep, dark water. But for spawning (laying eggs), they move to warmer, shallower water. The main time for ruffe to lay eggs is from mid-April to about June.
The Ruffe Life Cycle
The life of a Eurasian ruffe begins as an egg, just like other fish. The size of the eggs can vary. They are usually between 0.34 and 1.3 mm wide. The size depends on how big the female fish is.
If a female lays a second group of eggs in the same season, these eggs will be smaller. The first batch of eggs is about 0.90 to 1.21 mm. The second batch is about 0.36 to 0.47 mm. If a female lays eggs twice in one season, it is usually once in late winter or early spring, and again in late summer. The eggs hatch in 5 to 12 days if the water temperature is between 10–15 °C (50–59 °F).
Young Ruffe Development
The next stage is the embryonic or juvenile stage. Newly hatched embryos are very small, about 3.5 to 4.4 mm long. These tiny fish stay still for 3 to 7 days. During this time, they grow to about 4.5 to 5 mm long. One week after hatching, the young ruffe start to swim and eat actively. However, they do not swim together in groups at this age.
From here, the ruffe slowly grow until they are 2 to 3 years old. This is when they become fully mature. An adult ruffe is usually around 20 cm long. The biggest ones can reach 29 cm. Ruffe tend to grow more in clear, slightly salty water. Most female and male ruffe live for about 7 to 11 years.
Ruffe in the Great Lakes
The Eurasian ruffe has caused many problems in the Great Lakes area.
Ecological Effects of Ruffe
The ruffe's arrival in Lake Superior has caused a lot of damage. This fish takes up space and competes with other fish for food. Ruffe eat similar things to other fish. But they reproduce much faster. This means more ruffe in the water leads to less food for other fish.
Ruffe are special because they can live in many different habitats and temperatures. This helps them survive even with climate change or other changes in the environment. Ruffe also have an amazing ability to feel water vibrations. They do this using special organs called neuromasts. This helps ruffe find food and avoid predators. These organs become more sensitive as the ruffe grows older. This is different from perch fish, whose neuromasts get weaker as they mature.
The ruffe has the potential to take over from many other fish species. This could seriously harm the Great Lakes' ecosystem. If nothing is done, ruffe could ruin Lake Superior.
The ruffe was the first invasive species to be called a "nuisance" by a special program. It is now the most common fish in the St. Louis River basin. It has disrupted ecosystems all across the Great Lakes. Scientists first noticed this invasion in the 1980s. They believe the fish arrived in the Duluth, Minnesota harbor. It likely came in ballast water from large freight ships. Since then, studies show that ruffe and yellow perch are close relatives. They are quickly becoming rivals for food and space. The ruffe are winning this competition.
Controlling Ruffe Populations
Since the ruffe arrived in the Great Lakes, scientists have looked for ways to control them. At first, they tried to increase the number of Walleye and Northern Pike. These fish are natural predators of the ruffe.
Other ideas include using poison or chemicals. If a large group of ruffe is found, they can be poisoned. But if some survive, they will quickly reproduce again. Some chemicals can target specific fish species. For example, the chemical lampricide TFM kills ruffe but does not harm other fish.
The problem is that even a few surviving ruffe can move and start new populations. This issue will get worse if ruffe invade southern river systems. Scientists are now looking into using pheromones to control them. Pheromones are chemical signals.
After many studies, scientists found that ruffe are scared away by their own alarm pheromone. When a ruffe is hurt, it releases this pheromone into the water. This warns other ruffe to stay away.
Scientists have learned three key things about this pheromone:
- The pheromone does repel the ruffe.
- It only repels ruffe, not other fish.
- The pheromone can survive freezing temperatures. This means it could be used even in Minnesota's long winters.
By using this method, scientists hope to block ruffe from their natural mating spots. This could lead to a drop in their population. Their goal is to get rid of the species in the Great Lakes.
Other Places Ruffe Have Invaded
Ruffe were first found in Loch Lomond, Scotland, in 1982. They were probably brought there by people using them as live bait for pike fishing. Now, ruffe are very common throughout the Loch. People are worried about how the large ruffe population affects the native whitefish called powan (Coregonus lavaretus). Ruffe eat the eggs of the powan.
However, ruffe have also become a main food source for three other fish predators in the area. These are the great cormorant, grey heron, and northern pike.
See also
In Spanish: Acerina para niños
