European Bitterling Fish (Rhodeus Amarus)

European bitterling fish

Last updated on July 26th, 2022 at 11:26 pm

Bitterling fish, also known as Rhodeus amarus, can be found in the small streams of Eastern Europe. It’s a small fish that can fit in the palm of your hand, though it may grow to around 7 cm long if it is given plenty of room to grow in its natural habitat.

The European bitterling fish thrives in its watery environment but can survive in other locations if necessary. Although they have many predators and are not always successful in their reproduction, they are very adaptable and have numerous ways to defend themselves against harm or death.

If you haven’t heard of it before, the European bitterling fish (Rhodeus amarus) has some of the most amazing adaptability in the animal kingdom. Originating from Asia, bitterling fish have made their way across the Eurasian continent and over to Europe through the Atlantic Ocean, spreading to all kinds of bodies of water in the process.

The fish have managed to survive in these new environments due to one reason – their adaptability and ability to live in many different kinds of water and withstand many kinds of temperatures.

Rhodeus amarus, more commonly known as the European bitterling fish, may be small in size but it’s able to adapt to different types of habitats around the globe, including those with extreme environments. As an omnivore, it relies on both plants and animals in order to survive.

Its diet mainly consists of aquatic insects, crustaceans, and algae in freshwater systems while it also feeds on worms, mollusks, and insects in its marine habitat. This gives it the ability to adapt to different water conditions.

Origin and descriptions

European bitterling fish

European bitterling fish is a freshwater species native to central and northern Europe, where they live in small, cold streams that aren’t polluted. While sometimes referred to as minnows, these fish aren’t actually part of the group. In fact, there are many different species in their genus – approximately 16 – though most people only know about Rhodeus amarus. European bitterling fish also have an interesting range of adaptability: even when under stress, these creatures can still spawn at temperatures as low as 25°F!

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However, if conditions improve, they can reach up to 4 inches long. European bitterling is also an excellent game fish for some who enjoy recreational fishing.

With all of its amazing characteristics and survival mechanisms, it’s no wonder that several European countries give Rhodeus amarus endangered status. If you want to see European bitterling fish in action, just head to Europe, where you can watch fishermen catch them by hand; if you plan on doing so yourself, make sure your bait includes worms – European bitterling will eat nothing else.

Be careful handling these delicate creatures; catching them by hand is difficult because these medium-sized fish always move away from humans as quickly as possible.

Species profile

European bitterling fish are tiny fish native to European freshwaters, especially rivers. They have a remarkably wide range, living in Germany and Great Britain all across to Russia and Scandinavia, including countries like Poland, Switzerland, Germany, and even Norway.

They belong to a group called Cyprinids, which is a Cyprinidae family within fish known as Cypriniformes. The word Cypriniformes means like carp, a family also part of Cyprinids and known for their ability to breathe air.

As they’re generally small – between 5 and 10 centimeters long – they can avoid predators by hiding in river vegetation or small plants along riverbanks. However, if necessary, European bitterling fish can also move incredibly quickly through the water thanks to their powerful tails that enable quick acceleration.

Their diet consists mainly of algae as well as some seeds and small insects. They lay around 50 eggs each year and stay relatively close to their birthplace; young European bitterlings aren’t able to breed until after two years of life when they reach maturity.


The bitterling fish spends its entire life in freshwater. Even after it breeds, it doesn’t migrate into brackish or salty water. This habitat adaptability makes it easier for the fish to survive in freshwater without any adaptation. So even though many other species like salmon and trout move from fresh to saltwater, Rhodeus amarus remains in its home range year-round.


Growing to just 2.8 inches (7 cm) in length, these little fish are small but mighty. With their diminutive size comes an incredible ability to adapt quickly to a range of different habitats.

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Tank size

Due to their small sizes, the minimum recommended tank size for a European bitterling fish is 20 gallons (76 liters).

Tank requirements

Adult bitterlings are hardy, active fish that need plenty of room to swim and an environment with plenty of swimming space, plants, and rocks. They can be kept in tanks as small as 20 gallons or so; however, larger tanks with more surface area work best for these fish. Keep in mind that no matter what size tank you choose for your bitterlings, it will never feel big enough!

The bigger your tank is, however, the easier it will be to keep these wonderful fish healthy and happy. We have even heard stories of European bitterlings living happily in outdoor ponds! Just remember that if you plan on keeping your bitterlings outdoors, their water temperature must remain between 50°F and 64°F.

In addition, like all cold-water fish (goldfish being a popular example), bitterlings can easily get sick when exposed to high levels of ammonia. Make sure that you set up your pond properly and run regular partial water changes. If you ever decide to move them indoors, they’ll do just fine in most standard aquariums.

European bitterling fish tank mates

If you’re keeping a school of bitterlings, it’s important to pick tank mates carefully. These fish are territorial and will attack other members of their species; only house one male per tank unless you want to breed your bitterlings. The presence of a larger fish (one or two inches larger than your bitterlings) can serve as an additional defense mechanism and give your fish space from each other if they become aggressive.

Some good tank mates are dwarf danios, dwarf species of barbs, and many catfish. Avoid plecostomus, larger species of barbs, and large danios; these fish will bully or out-compete your bitterlings for food.


European bitterling fish

A key part of being able to breed bitterlings is having clean water. Keeping your water clean means it has fewer harmful bacteria, which allows your fish to breed. If you want to ensure breeding and then successful fry, do everything in your power to keep your tank free from any pathogens.

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The female bitterling lays approximately 200 eggs at once, which she attaches to twigs and vegetation in shallow water. The male then guards these eggs for about a month before they hatch and disperse into surrounding waters. If left undisturbed by predators, bitterlings typically live up to three years old.

This species is one of the few fish that can reproduce without needing water—the larvae are known to be able to survive for extended periods out of the water as long as their gills remain moist.

These adaptable fish have actually become popular with hobbyists who keep them in aquariums or small home ponds due to their hardiness when kept in captivity.

Are they aggressive or peaceful?

They are peaceful in nature. It’s true that bitterlings can be a bit nippy in their younger years. They are a lot like cats in that they don’t like to share and will sometimes fight over territory and food. As they grow older, however, they become more docile and will choose peace over violence any day. If you happen to have more than one fish swimming together with their young, it may be hard for them to break away from these behaviors later on.

European bitterling fish care

European bitterling fish

Due to their small size, bitterlings are a very challenging species to care for, but if given adequate food and space, they can thrive. They need a large surface area (but not as much surface area as other fish), at least 1-2 inches per fish; they do well in densely planted tanks with plenty of hiding places or caves, but will readily adapt to sparsely decorated tanks.

Make sure that you aren’t keeping them too warm! Temperatures above 74 degrees Fahrenheit can damage a bitterling’s system, which could lead to death. Your tank should have powerful filtration and moderate water movement.

Don’t be afraid to maintain your water quality by adding algae eaters like algae catfish or Otocinclus—they won’t hurt your fish, but they will keep it clean.

The bitterling fish survives in nutrient-poor and variable conditions, due to their ability to adapt to changing environments. The freshwater species are able to absorb energy from food sources that are up to 4% protein, meaning they can thrive on very little nutrients.

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They also have a number of adaptations that allow them to survive in warm, polluted water; they’re even known for surviving out of water for more than two days!

It’s thought that these genetic adaptations came about as a result of local competition between different Rhodeus populations: when resources are scarce or fluctuate greatly, it is only natural for organisms to become specialized towards either exploiting prey with high nutrition or being able to extract every last bit of nutrition from low-nutrient prey.

What they eat

As an omnivore, a European bitterling fish will consume a variety of foods such as insect larvae, crustaceans, and plant matters. This species mainly eats insects and small invertebrates in its freshwater habitat. They do not actively hunt for prey; instead, they rely on their exceptional sense of smell to locate food sources. Once an aquatic insect has been detected, a European bitterling moves quickly to intercept it, using senses other than sight.


The European bitterling fish can live up to 7 years if conditions are optimal.

Parasites and diseases

European bitterling fish

Parasites can live in our European bitterling fish causing many diseases including gill rot and ulcers. As a result, most anglers clean their bitterling thoroughly before cooking. However, some parasites can be harmful to humans as well. A parasite called Anguillicoloides crassus will infect human hosts through eating undercooked fish; it attaches itself to human intestines and leads to an infection known as eelworm disease.

Do they make good pets?

European bitterling fish can be kept as pets, but it should be noted that they are schooling fish, and, so ideally, would need to be kept in a group. They also grow to just under 4 inches in length, so a tank of at least 20 gallons with an air-powered sponge filter and lights is recommended. Bitterlings prefer clean water, so some additional effort may be needed on your part to keep them healthy.