Scuds in Aquarium: What Are Scuds & Tips to Control Them

Scuds on the aquarium floor among debris

Scuds are tiny shrimp-like creatures that sometimes unknowingly end up in your aquarium. These tiny wrigglers can add a natural look to your aquatic environment but can quickly become troublesome if not managed.

In this guide, we’ll walk you through everything you need to know about scuds, from their appearance and behavior to ways in which you can control their presence in your aquarium.

What Are Scuds and How to Spot Them?

Group of scuds with varying shades and transparencies

Scuds, scientifically categorized under the Amphipoda order and commonly known as Gammarus shrimp, are tiny, versatile crustaceans found in freshwater, brackish, and saltwater environments.

They are also known as side-swimmers due to their distinctive movement in the water.

These small shrimp-like creatures are typically bottom-dwellers and can be introduced into aquariums via the addition of new plants or substrates, often going unnoticed until they breed and increase in numbers​​.

A scud’s size ranges from 1 to 8 millimeters. They go through a complex life cycle, shedding approximately every five days, and can live up to two years under optimal conditions. They are adaptable to cooler water, which can slow down their life cycle and extend their lifespan​​.

Scuds are generally transparent, sometimes with a greenish hue. They may also appear slightly brown to blend with their environment.

Physically, they resemble small, shrimp-like sowbugs without a carapace, which is the hard shell that covers some crustaceans like crayfish.

They have two pairs of antennae, and their bodies are divided into seven segments, each having a pair of legs.

Scuds breed rapidly and can become a problem in tanks if not properly managed​​. They are omnivores and detrivores and consume various materials, including decaying plant matter, algae, live plants, and even small fish or fish fry.

This broad diet means scuds can be beneficial for cleaning an aquarium but can become pests, particularly when they feed on plants like moss.

How Do Scuds Get in Your Aquarium?

Scuds can sneak into your aquarium in a few unsuspecting ways. The most common way they get into your tank is through the addition of live plants. These tiny critters are excellent at hiding among leaves.

Used substrates are another typical entry point. Hobbyists often use substrates from their main tanks to speed up the cycling process of a new aquarium, which can unwantedly introduce scuds that are buried within it​​.

Filter media from another tank can also harbor scuds. When transferring media to a new aquarium for its beneficial bacteria, scuds may come along, too, so it’s wise to rinse and inspect this media before use​​.

Lastly, scuds can arrive with new fish or second-hand equipment that hasn’t been properly cleaned.

When adding new fish, the water from the store may contain scuds and second-hand equipment like lights and heaters could also be hiding these small amphipods.

Benefits of Scuds in an Aquarium

Scud moving through aquatic vegetation in a tank

While scuds can initially be introduced unintentionally, their presence can offer a range of benefits to your aquarium.

They not only contribute to the biological diversity and balance within the aquarium but also offer practical advantages that can help reduce maintenance efforts and improve the overall health of the tank.

Let’s delve into the specific benefits scuds provide:

  • Serve as food sources: Scuds serve as live food for many fish species, providing a natural and nutritious option that can help fish thrive​​.
  • Help in algae control: They actively consume algae, including diatoms and green algae, helping to control its growth and maintain a cleaner aquarium​​.
  • Eat detritus or waste: By eating detritus, which includes fish waste, uneaten food, and dead plants, scuds help keep the tank environment clean​​.
  • Mitigate bacterial populations: Scuds aid in maintaining water quality by consuming bacteria that can otherwise proliferate and cause disease​​.
  • Help in decomposition: As generalist feeders, scuds break down a wide range of organic materials, contributing to the decomposition process within the tank.

Scuds are not only self-sustaining organisms but also beneficial additions in tanks. They manage waste, control algae, and serve as food sources, creating a more natural environment in aquariums.

However, careful management is crucial as they come with caveats, such as their tendency to consume live plants and small invertebrates.

The Impact of Scuds in an Aquarium

As established, scuds can be beneficial to aquariums. However, if not managed, they can also adversely impact your tank, specifically your aquarium inhabitants, plants, overall aesthetic, and water quality.

Aquatic Plants

Scuds in an aquarium have a mixed impact on aquatic plants. These tiny crustaceans are efficient at cleaning up dead plant matter, which keeps the tank tidy and prevents the decay that can negatively affect water quality. 

However, scuds also have a taste for live plants, particularly those that are soft, like moss.

To protect your live plants, it’s advisable to ensure scuds have enough alternative food, like algae, to prevent them from turning to your plants for sustenance.


Scuds serve as a live, nutritious food source for various fish species in an aquarium. Some fish species that prey on scuds include betta fish, killifish, tetras, and mollies.

These fish enjoy hunting and consuming scuds, which can stimulate their instincts and contribute to a balanced diet. However, care should be taken in breeding tanks, as scuds may also prey on fish eggs and fry if the population is not managed.

Thus, while scuds can be beneficial in providing nutrition to adult fish, they must be kept in check to protect vulnerable fish populations.


Scuds in an aquarium can pose challenges for shrimp. They compete directly with shrimp for food and habitat space, which can be a significant problem in smaller tanks.

They are aggressive feeders and can outcompete shrimp for detritus, algae, and biofilm, which are also primary food sources for shrimp.

There’s also a risk during the shrimp’s vulnerable molting phase, where scuds may prey on them. This competition and risk can disrupt shrimp breeding efforts and may lead to a decline in shrimp population.


While scuds typically feed on detritus and decaying matter, they have also been observed to interfere with snails and their eggs. This is especially true in tanks where scuds outnumber the snails, leading to competition for food.

If snails are an intended part of the aquarium for their algae-eating or aesthetic value, you must carefully manage scuds. This ensures that snails and scuds can coexist without one group outcompeting the other.

Nevertheless, you should not be concerned about scuds if your snails are large species and have trapdoors to protect them, such as nerite snails and ramshorn snails.

Competition for Food

You do not have to worry about your fish competing for food with scuds since these little critters serve as live food sources for various fish species.

However, they can become a problem if your tank has other detrivores that rely on similar food sources.

Scuds are known for their voracious appetite, feeding on a wide range of organic matter. This can lead to significant competition for food among aquarium inhabitants, particularly when scud populations are high.

They compete with other detritivores, such as shrimp and snails, for decaying plant material, leftover fish food, and algae.

Shrimp, especially young ones, may not venture out as boldly as scuds, which can monopolize food resources. Snails might also find it challenging to maintain food intake if scuds overrun the environment.

Tank Maintenance

These amphipods play a dual role in tank maintenance due to their dietary habits. As detrivores, they feed on detritus, which includes decomposing plant matter, fish waste, and leftover food.

This activity can help keep the tank cleaner by breaking down potential waste that would otherwise accumulate and affect water quality.

However, the presence of scuds can also present challenges. Their population growth needs to be monitored, as an overabundance can lead to overgrazing of beneficial bacteria and live plants.

This can potentially disrupt the balance of a carefully maintained aquarium ecosystem.

Water Quality

Scuds can have a significant influence on the water quality of an aquarium. They consume decaying organic matter, which can help reduce waste buildup and potentially lower ammonia levels.

This waste breakdown process performed by scuds is beneficial as it can lessen the burden on the aquarium’s filtration system.

On the other hand, if scuds multiply too rapidly, they can contribute to deteriorating water quality by producing more waste than they consume.

This can increase ammonia and nitrate levels, which are harmful to fish and other aquarium inhabitants at high concentrations.

Aquarium Aesthetics

Whether scuds positively or negatively impact aquarium aesthetics largely depends on your preference.

Scuds, when kept at manageable levels, can add to the natural aesthetic of an aquarium by mimicking the bustling activity found in wild aquatic ecosystems.

Their swift movements and scavenging behavior can offer a glimpse into the complexity of aquatic life, providing an engaging display for observers.

However, an overpopulation of scuds can detract from the aquarium’s visual appeal.

Excessive numbers can lead to visible swarms that overwhelm the tank, detracting from the beauty of fish and plant life. This can make the aquarium appear untidy and poorly maintained.

In short, if you want a more natural-looking aquatic environment, you might find the presence of scuds visually pleasing. However, you might see scuds unwelcome if you prefer your tank water to look crystal clean.

Reproduction and Habitat of Scuds

Scud in a curved posture attached to a plant in a tank
Image credit: maki_save / Instagram

Scuds reproduce quickly and can thrive in various habitats within an aquarium. They are not picky about where they live as long as they have access to food sources like detritus, algae, and biofilm.

These adaptable creatures prefer to dwell at the bottom of the tank, often hiding beneath substrate or within plant leaves.

Their reproductive rate is high, which means they can quickly populate an aquarium. They reproduce through external fertilization; males release sperm into the water, which females then take into their brood pouch to fertilize the eggs.

A female scud carries the eggs for one to three weeks before they hatch and is capable of reproduction as early as three weeks old.

This efficient breeding process can lead to a rapid increase in their numbers, making it easy for them to establish a stable presence in their environment.

In the wild, scuds are diverse and adaptable, making nearly every freshwater habitat their home. These creatures are found in various water bodies, from shallow rivers and streams to lakes, ponds, and swamps.

They are not just limited to fresh waters; they also inhabit saline waters, hot springs, and the underground waters of caves, indicating their incredible adaptability​​.

How to Get Rid of Scuds in Your Aquarium

Albeit beneficial to aquariums, scuds can become a real nuisance when not properly managed. They can greatly impact the balance in your tank negatively, which may force you to take action and eradicate them.

Here are some ways you can do to get rid of scuds in your aquarium:

Preventive Measures

To prevent scuds from entering your tank, start with quarantining. Every new plant, fish, or decoration could bring these pests, so keep them in a separate tank for a few weeks to monitor for scuds.

When reusing filters or aquarium media from other tanks, ensure that they are thoroughly cleaned, as they can also be hiding places for scuds you might unintentionally introduce to a new tank.

You should also manage your tank’s food supply. Overfeeding leads to leftovers, which scuds feast on. Feed your fish amounts they can eat in a few minutes, and remove any uneaten food promptly.

Also, keep your tank clean. Regularly change part of the water and vacuum the substrate. This reduces food sources and hiding spots for scuds, keeping your aquarium healthy.

Pro Tip: Ensure you’re well-prepared for new plant or fish additions by having a quarantine tank, filter, and essential aquarium equipment readily available. This quarantine tank can also serve as a crucial isolation space for sick or infected fish.

Manual Removal Techniques

Manually removing scuds from an aquarium can be done effectively with a few simple tools and techniques.

To start, create a net trap using a safe food item, like a slice of zucchini or carrot, as the bait. Place the trap in the tank before lights out, as scuds are nocturnal.

Overnight, they’ll gather on the bait, allowing you to remove them easily when you retrieve the trap in the morning.

A gentle approach with a small net can also be effective. Move slowly to catch them without disturbing or stressing your fish. Nonetheless, you may need to repeat this method several times.

I have also found success in using planaria traps to manually reduce the population of scuds in my aquarium.

Although they are specifically made for worms in aquariums and not for scuds, I found them surprisingly effective in trapping these critters.

Routine substrate cleaning with a siphon can also help catch scuds hidden in the gravel. This not only removes scuds but also keeps the tank clean, which naturally discourages scud proliferation.

Here is how planaria traps work in trapping scuds:

Natural Control Methods

You may also consider introducing fish species that eat scuds as a natural means of controlling their population. Species like betta fish and killifish are adept at hunting scuds but may not be suitable for community tanks.

In my case, I lean towards more sociable fish such as tetras, mollies, and certain cichlids in controlling the scud population in my tanks. These fish species also feed on scuds and are a better fit for diverse aquariums.

However, I am quite conscious that they could also prey on other small invertebrates in your tank. Hence, you should still be cautious if you plan on using them as a natural control method.

In aquariums that support a broader ecosystem, some amphibians or insects could also serve as scud predators. For example, newts and tadpoles in larger, naturalistic setups might prey on scuds.

Before adding new predators, research thoroughly to ensure they won’t disrupt your tank’s balance or outcompete your existing pets for food and space.

Employing these natural predators should be part of an integrated approach that includes maintaining excellent water quality and regular tank maintenance to reduce the conditions scuds favor.

Chemical Control Methods

Chemical methods for controlling scuds in aquariums should be used with extreme caution. Most chemical treatments that can eradicate scuds are also harmful to other aquarium inhabitants.

It’s crucial to avoid using harsh chemicals that can disrupt the delicate balance of your aquatic ecosystem.

Here are some chemical approaches you can take to manage scuds in your tank:

1. CO2 Nuke with Carbonated Water

This method requires you to first relocate all aquatic life to a secondary tank. Then, reduce the water level in the main tank to just above the substrate.

Gently pour carbonated water into the tank to increase the carbon dioxide concentration, which will suffocate the scuds. The pH of the water may spike, so it’s critical to monitor and adjust as necessary.

After 24 hours, perform several water changes to expel the excess CO2, gradually restoring the tank to its safe, original condition before returning your aquatic life.

2. Copper Treatment

Begin by transferring all inhabitants to a separate tank. Test the water with a copper test kit, then carefully add copper sulfate to the tank, aiming for a concentration between 1.5 and 2 mg/L.

Leave the copper-treated water for three days to ensure all scuds are eliminated. Afterwards, carry out substantial water changes to bring down the copper levels.

Test the water again to ensure it’s at a safe concentration for your fish and invertebrates before you reintroduce them.

3. Hydrogen Peroxide Cleaning

This treatment also requires an empty tank. After moving all creatures to a safe location, use hydrogen peroxide to rigorously clean the tank, decorations, and equipment.

Allow all items to dry under direct sunlight, which helps to decompose any remaining hydrogen peroxide. It’s also advisable to replace the filter media before returning your fish and plants to the tank.

These chemical interventions are drastic and should be carefully considered. They demand attention to detail and a controlled environment to avoid harming the delicate balance of your aquarium ecosystem.

After each treatment, it’s essential to ensure the tank is habitable, with appropriate water conditions, before reintroducing any aquatic life.

Tips for Achieving Balance With Scuds in Your Tank

Transparent scud clinging to a stem in an aquarium
Image credit: imlichentoday / Instagram

Achieving a balanced relationship with scuds in your aquarium is possible with careful management. Here are some ways on how to do it:

  • Monitor your feeding habits. Overfeeding leads to excess food, which scuds thrive on. Feed your fish just enough, and promptly remove any leftovers to limit scud food sources.
  • Introduce natural scud predators. Certain fish or invertebrates that are compatible with your aquarium community can help keep their balance. These predators will help keep scud numbers in check without upsetting the tank’s ecosystem. But be cautious about the balance, as over-predation can lead to other issues.
  • Maintain your tank’s cleanliness regularly. Regular cleaning, including substrate vacuuming and water changes, keeps the environment unfavorable for scud overpopulation.

A healthy, well-maintained tank naturally controls scud numbers, promoting a balanced ecosystem where scuds can play their role without becoming a nuisance.

Frequently Asked Questions

Scud suspended on a leaf in an aquarium
Image credit: maki_save / Instagram

What Do Scuds Eat?

Scuds in an aquarium mainly feast on algae and decaying organic matter, such as plant debris and uneaten fish food. These tiny crustaceans will also scavenge on dead fish and fish waste, helping to keep the tank clean. 

But they can be a bit of a nuisance, too, sometimes munching on live plants or vulnerable small creatures like shrimp larvae. It’s this hardy appetite that often requires their populations to be kept in check within the aquarium.

Do Scuds Need Light?

Scuds are adaptable creatures and do not require light to survive. They can function and find food in the dark, as they often do in their natural habitats like streams and lakes.

However, light can be beneficial in an aquarium setting as it encourages the growth of algae, which is a primary food source for scuds.

Therefore, while scuds don’t need light, providing it can enhance their food supply and, by extension, improve water quality by reducing algae levels​.

What Do Scuds Need to Survive?

Scuds are not demanding inhabitants for an aquarium. They require stable water conditions with a moderate temperature, between 18°C and 24°C (64°F to 75°F), and a pH level from 6.5 to 8.0.

They also need a tank with a substrate that allows them to burrow and plant or rock hideaways where they can seek shelter.

While scuds can share their space with many fish, it’s important to avoid pairing them with species that might see them as a snack.

With these needs met, scuds can survive and even help clean your aquarium by consuming algae and detritus.

How Quickly Do Scuds Reproduce?

Scuds have a high reproductive rate, especially in warm aquarium conditions. Females carry fertilized eggs in a pouch, with hatching occurring within one to three weeks.

The juveniles can mature quickly, often becoming capable of reproduction themselves just three weeks after birth.

This efficiency means scud populations can increase swiftly, sometimes leading to overpopulation in tanks if not managed.

Overall, scuds are wonderful creatures that can positively contribute to your aquarium. However, careful management is crucial to manage their negative impacts. Got any more questions? Comment them below!

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