Scuds in Aquarium: What Are They & How To Control Them




scuds in aquarium

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Scuds are small, shrimp-like creatures that belong to the family of Gammaridae. But what exactly are they, and how can you control their population in your aquarium?

While these little creatures are amazing at eating algae and acting as a clean-up crew, they also have high reproductive rates that can be difficult to manage.

Also, they’re almost impossible to get rid of once established, and their endless appetite might cause problems for shrimp, fish, and planted tanks.

In this article, I’ll take a look at how scuds get into your aquarium and share some tips for controlling their population. I’ll also explore different methods of getting rid of them if they become a problem in your tank.

What Are Aquarium Scuds?

Scuds are small shrimps of the Amphipoda family, also known as side-swimmers or Gammarus shrimp.

There are several species of scud, but the one I will be focusing on is the Gammarus Genus from the Gammaridae family, of which there are over 200 species.

Although scuds are typically freshwater creatures, there are many species that can adapt to brackish or saltwater environments.

These amphipods are small and bottom-dwelling often found in rivers, lakes, ponds, and swamps. In fact, you can find them almost anywhere – they’re very versatile!

If you’ve ever been to the beach at night, you may have seen these guys jumping around in the sand. These nocturnal animals are also known as sand fleas or sand hoppers, and they can often be found near light sources in large numbers.

How Did Scuds End up in My Aquarium?

Scuds often hitchhike on live plants from your local fish store, or if you have used substrate, they might already be in there.

Also, if you ever get used to aquarium components like filters or decorations, scuds could have been in those items, too.

Scuds Habitat

Scuds are commonly found in salt water, hot springs, and underground cave waters. They have colonized almost all freshwater ecosystems and can be found in rivers, streams, lakes, ponds, swamps, and man-made canals.

In their natural habitat, scuds live among stones or vegetation for protection from fish predators.

How Can I Identify Scuds in My Fish Tank?

Typically, scuds look transparent, but you might see some green because of their digestive tract. Also, scuds may look slightly brown to help them camouflage and stay hidden from fish that would eat them.

Although scuds are commonly called shrimp-like amphipods, this isn’t entirely accurate. Unlike shrimp, they don’t have a carapace and their body is fully segmented and divided into 3 categories:

  1. The cephalothorax includes the head and two pairs of antennae.
  2. The thorax is the grouping of the body’s seven segments, each containing a pair of legs.
  3. The abdomen consists of the six segments that make up the rear end. Each segment has webbed appendages to help with swimming.

What Is the Maximum Size Scuds Can Grow To?

Different scud species can grow to diverse sizes. However, the average size of a scud in an aquarium is 10-20 mm (0.4-0.8 inches).

Life Cycle of a Scud

Gammarus shrimp have a 9-tiered life cycle, starting from 1mm and ranging up to 8mm when fully grown. In between each stage, the shrimp will molt its skin-a process, which takes place every 5 days on average.

Depending on their living conditions, a scud will usually live for around a year but can potentially survive for 2 years.

Gammarus shrimp thrive in cold water, with their lifespan increasing and their life cycle slowing down. However, they can’t survive when temperatures reach freezing.

The Pros and Cons of Scuds in an Aquarium

According to your aquarium’s setup, you may or may not want scuds present. The table below displays some pros and cons of having scuds in your fish tank:

Impacted Area of AquariumBenefits of ScudsDrawbacks from Scuds
General Fish PopulationMost fish will enjoy eating scuds as a source of live food. Fish enjoy hunting them as they would in their natural habitat.None
Baby Fish & ShrimpNoneScuds will attack and feed on baby fish and shrimp that have recently molted and lost their protective shell. Baby shrimp are at the most risk.
Aquarium PlantsScuds will eat decaying matter, including plant matter.If you enjoy having moss planted in your tank, scuds will be unwanted as they enjoy feeding on moss. Scuds typically come in large numbers and will swarm all over your moss until there is little left.
General Tank WasteScuds will eat decaying matter in a tank and help stop the build-up of ammonia. They will often find their way into your filter to feed off the sponges.Larger scud colonies will surely leave behind some waste of their own, contributing to ammonia build-up and lower oxygen levels.
General Aquarium AestheticSome aquarists like how they look, and they are a welcomed addition to the aquarium.Some aquarists feel they are ugly and are not a welcomed addition to their aquarium.
FeedingScuds will eat any leftover food waste, which will help keep the tank clean.Large scud colonies can compete with smaller fish for food.

The Typical Behavior of Scuds in an Aquarium

Scuds are usually introduced into your freshwater tank when adding new plants. Baby scuds can hide, unseen within plants.

When added to your aquarium, scuds will start to breed. They especially love eating moss, so be sure to keep an eye out for them if you’re planning on adding any new plants to your tank.

Typically, scuds bury themselves in the gravel at the bottom of aquariums to hide from other fish. If their numbers start growing rapidly, you will begin noticing them more.

Also, these pals are opportunistic eaters and will crowd over any food they can find. Further, they reproduce quickly and can soon devour all the Moss in a tank if left unchecked.

What Food Do Scuds Eat?

Even if you don’t want them in your tank, it’s beneficial to know what scuds eat. Since they’re omnivores, scuds will consume anything they come across. Also, since they’re scavengers, the easier the meal is, the more appealing it is to them.

Scuds will clean out any waste present in your aquarium. Their diet consists of decaying plant matter, algae, live plants, rotting fish food particles, and small live fish or fry shrimp larvae.

Also, scuds tend to consume a variety of plants, which can be detrimental in an aquarium setting. If you’re like many aquarists who enjoy having moss in their tanks, you may be disappointed to find that scuds are especially fond of eating it.

Many people enjoy smaller fish in their tanks or want to try their hand at breeding. However, this isn’t a good idea with scuds, as they will happily attack smaller fish or fish fry, especially when the scuds are larger in numbers.

How Can I Remove Scuds From My Aquarium?

Catch and Remove Them

Scuds are easily caught with the right trap, and once they’re in, it’s hard for them to escape. I’ve recommended these traps to many fish tank owners, who were then able to remove large numbers of scuds effectively:

Manual Removal Trap

To make your own scud trap, you can follow these simple instructions:

  1. Place the net at the bottom of the tank
  2. Place a small piece of blanched cucumber, zucchini, green beans, carrot, cabbage, or lettuce in the net. Let it sit for some time.
  3. You will have a lot of scuds on the food within a couple of hours.
  4. Bring the net along with the food inside.
  5. Remove the scuds or give them to your fish.
  6. Keep going until you’re happy with the results.

However, the downside to this method is that more creatures will always be caught in your net, including shrimp and snails.

Planaria, Scud, and Shrimp Trap

Although you could use a net, it’s unlikely to be very effective in catching scuds. These freshwater amphipods are elusive and quick, making them experts at hiding.

Often, they’re found buried deep within the substrate at the bottom of your tank.

If you’re having trouble removing scuds with a net, some people have found success using a turkey baster instead. This is because the baster allows you to suck the scuds up into the nozzle.

Another method I’ve tried (and heard about) is baiting them at the bottom of the tank. As they attach to the bait, remove it from the tank to get rid of scuds effectively.

If you want to attract them, boil a carrot or another food. When it becomes soft, poke a skewer through it and leave it at the bottom of your tank.

After some hours have passed, check the progress of your carrot (or whatever bait you used).

By now, a good chunk of the scuds in your tank should be munching on the bait. You can normally take out the bait while the scuds are still attached if you’re careful with your movements and don’t jar anything. Afterward, rinse off the bait and return it to the tank.

You can do the above process as many times as you’d like until you find only a handful of the little critters feeding. Doing this will significantly decrease the number of scuds in your tank.

By using the baiting process, you’re more likely to be successful if you keep your tank’s light off. Even though scuds are quite timid animals, they will hang on to the bait as long as they feel unthreatened.

Although baiting scuds won’t completely remove them from your tank, it will lower their numbers until they start breeding again.

Clean Your Tank, Plants, and Gravel

Regularly cleaning your tank, plants, and gravel is another method of removing scuds. Scuds are commonly found in algae growths or on the bottom, so sweeping these areas will catch them before they can burrow back to safety.

When cleaning your tank and plants, make sure you don’t use harsh chemicals that could harm your fish. Just rinse them thoroughly with water and a soft cleaning brush. Also, you can use a plant bleach dip for particularly stubborn scuds.

Once you get to the gravel, you can place a tube at the bottom of your tank, suck up the scuds from below, and then rinse them off before returning them to your aquarium.

While this method is not foolproof, it’s an effective way to decrease scud numbers and keep your tank clean.

Afterward, check your filter and clean the sponges with hot water to prevent scuds from feeding off the waste your filter has trapped. If you use bleach, make sure to rinse it off completely before adding it back to the tank.

Increase CO2 Levels in Your Tank

A common, though less-than-humane way to kill scuds, is by cranking up the CO2 levels in your aquarium, essentially causing them to suffocate.

For this simple trick, you will need an extra tank, as it not only kills scuds but fish too. When moving your fish to the spare aquarium, make sure the water has been properly circulated and levels are within acceptable parameters.

Also, your fish should only be in the temporary tank for about an hour, so transfer some water from the main tank before transferring your fish.

In order to raise the CO2 levels in your tank, pour 1/2 liter (or more) of carbonated water into it. Be sure that you use seltzer water without any additives. Soda or tonic won’t work because they will poison the already contaminated water.

After adding carbonated water, the CO2 levels will rise sharply and remove all dissolved oxygen from the tank. Within 45 minutes to an hour, all scuds should suffocate.

Before you return your fish to the main tank, check the oxygen levels. If they haven’t returned to normal, then proceed by creating bubbles at the surface or using other methods to encourage oxygenation before returning your fish.

Use Extreme Cold

A cold shock is another way you can kill scuds in your aquarium. Scuds are cold-blooded creatures, so exposing them to extremely low temperatures will cause exothermic reactions that will ultimately lead to their death.

However, this method can damage your plants and kill your fish, so it may not be the best option for you if your tank is heavily planted or has a lot of live fish.

Introduce Scuds Eating Fish

scuds in aquarium

Scuds can make a nice snack for omnivore fish. Similar to how a farmer needs his horses and cattle to eat the grass, you can use fish to manage the scuds in your tank.

However, note that this is only possible if you don’t keep small shrimp or fish because they will be eaten by the larger predator fish.

Some scud-eating fish you can try include the following:

The only downside to this method is that you have to intentionally add a new fish to your aquarium, which may not be an undesirable addition.

For example, Cardinal tetras and Guppies are small fish, but they’re still too big for shrimp tanks and will likely eat them all.

Even if you have a large tank, fish might not be able to completely get rid of them and it will take some time. I saw reports that not even Cherry barbs, Livebearers, Loaches, and Cories could eradicate them in a 40-gallon tank (160 liters.).

Excel Overdose

Some people have attempted to rid their tanks of scuds by using Excel at a rate that is ten to fifteen times the normal amount.

However, glutaraldehyde (the active ingredient in Excel) is a biocide that can cause chemical burns when it comes into contact with tissues.

To give you an idea of how potent this substance is, biocides are also used for sterilizing some medical instruments.

Also, a heavy dose of Excel will kill shrimp, snails, fish, and even some plants (like Vallisneria, mosses, Subwassertang, etc.). So you’ll need to remove everything from the tank.

However, beware – even when everything seems dead, some scuds may have survived! They can hide deep in the substrate, so be sure to stir it up before adding anything back into the tank.


Copper is poisonous to fish and shrimp, as well as all crustaceans. This includes dwarf shrimp, crabs, and crayfish–all of which are especially sensitive to the metal. For this method, you will need to do the following:

  • Buy a copper test kit
  • For the most effective treatment, lower the water volume in the tank as much as possible
  • Add Copper sulfate to the water. The concentration should be at least 1.5 – 2 mg/l (or 5 – 2 ppm)
  • Allow the tank to sit for three days
  • Change your water, and be sure to fill up your tank
  • Test the copper level again and see if it has increased
  • Prior to reintroducing fish or shrimp, you must remove the copper

While this method has its benefits, it also comes with the cost of any leftover copper poisoning and killing the Dwarf shrimp when you move them back.

AlgaeFIX Overdose

Although people suggested that AlgaeFix might help with scuds, I couldn’t find anyone who had actually tried it.

However, AlgaeFix comes with a warning – do NOT use AlgaeFix with any type of crustacean, including crabs, shrimp, freshwater shrimp, and lobsters.

But this is exactly what we need! Even so, don’t assume that an overdose of AlgaeFix is safe for fish or snails. Make sure to remove them from the area before using the product.

The Nuclear Option

Finally, if all else fails, you can try using a nuclear option to get rid of scuds. In this method, you will need to do the following:

  • All your shrimp, fish, and snails should be moved to another tank (quarantine tank) that doesn’t have any decorations or gravel
  • Make sure that no scuds have been transferred
  • Take everything apart and see how it works
  • Get your fish tanks, decorations, and driftwood sparkling clean with hydrogen peroxide
  • Let them air dry in the sun for a few days
  • Dispose of the sponge (Replace the filter media)
  • Quarantine plants
  • Quarantine shrimp
  • If you’re thinking about reusing substrates from an infected tank, boiling it or pouring boiling water on the substrate are both effective methods of killing bacteria. Stir the substrate to make sure everything is covered

How Can I Keep My Tank Scud-Free?

The best proactive measure against scuds is to quarantine everything that may come into contact with your fish tanks. This includes fish, shrimp, crayfish, crabs, snails, plants, driftwood decorations, and more.

If it has been in another environment where there was any potential for exposure to biological matter, treat it as if it is infected.

If you maintain a consistent quarantine, you’ll be able to control scuds. Some aquarium experts will tell you that overfeeding is the root of the problem and therefore propose stopping this bad habit as a way to eliminate scuds.

While I do agree that overfeeding shouldn’t take place in fish tanks, I don’t think it’s effective in solving scud problems. In some experiments, scud species have survived for up to 10 days without food!

How Can I Raise Scuds in My Fish Tank?

Feeding fish and dwarf frogs? Scuds have you covered! Not to mention, they can thrive anywhere, making them the perfect candidate for home cultivation. The best part is: it won’t cost you an arm and a leg. Here’s how you can bring up scuds:

  • Tank size: While there are no minimum requirements, it will be easier to care for your plant if you have 2.5 – 5 gallon tanks (10 – 20 liters)
  • Filtration: Scuds are tiny creatures, much like shrimp. Large pore sponge filters will serve as the best choice because they don’t produce a lot of waste themselves. Not to mention, they’re cheap and easy both to maintain and clean. Plus, they provide plenty of surface area for them to graze and live!
  • Aeration: The current should be minimal–just a few bubbles every 1 or 2 seconds
  • Substrate: Although any type will do, coarse gravel will provide more opportunities for them to hide and be happier as a result
  • Driftwood and décor: The more options you provide, the better. Having multiple feeding areas and hiding places will let them feel more comfortable and secure in their new home
  • Plants: The more plants you have, the better. This will give your scuds more places to hide and feed. However, remember that scuds can eat plants when they are hungry, so don’t add any plants that you want to keep safe from them
  • Lighting: The amount of light isn’t as crucial for scuds. Instead, you should adjust the lighting to better suit the plants and algae in your tank
  • Water Parameters: Scuds are known for their durability, but the following tips will help optimize results:
  1. Temperature: 20 – 24 °C (68 – 74 °F)
  2. pH: 7.0 – 8.0
  3. Hardness: GH>10
  • Calcium: You can add crushed corals and cuttlefish bones to help provide calcium for their shells
  • Feeding: A few times each week, give them small amounts of food. Do not overfeed them, as leftovers can spoil the water. They may enjoy fish food, shrimp or crab food, algae wafers, blanched vegetables, and more
  • Maintenance: Keep your water parameters optimal by checking them regularly and doing 10-20% water changes. For scuds tanks, it’s important to only use dechlorinated water

How Rapidly Do Scuds Breed?

The answer to this question largely varies depending on the species in question. For example, if we examine Hyalella Azteca (one of the most common freshwater scuds used for culturing), they reach maturity at 3 weeks old following their 6th molt.

Additionally, females of this species tend to be smaller than males.

After a female molts, the scuds mate. Adult males have an intermoult period that lasts anywhere from 8 to 43 days, and females carry them on their backs for 10 to 13 days before they molt.

During molting, males help females to rid the old exoskeleton before departing after fertilization. Typically, the incubation period is approximately 11 days when at 20°C (68F).

However, it’s worth noting that temperature changes will impact a scud’s metabolic efficiency rates, which are higher in warmer temperatures.

Generally, female scuds lay 20 – 30 eggs, but some large females are able to lay more. After hatching, juvenile scuds reach a maximum length of 1 mm and they develop the skills to take care of themselves rapidly.

Can Scuds Endanger Shrimp Populations?

Scuds are harmful to shrimp and should not share the same tank if you want to breed them. Do not believe anybody who says that scuds are great for planted or shrimp tanks because they’re not. I’ll explain why below:

Food Competition

Primarily, scuds and Dwarf shrimp compete for the same things: food sources like algae, detritus, and biofilm. Also, because they have similar tastes in resources and occupy the same spaces, it creates more competition.

In addition, small baby shrimp are the ones who would suffer the most from this problem. They prefer to stay hiding in one place for a period of several days.

They don’t brave swimming out into the open, which limits them to only being able to eat floating particles, algae, or biofilm that are close by.

Breeding Competition

Scuds breed quickly and their reproduction cycle is shorter than shrimps, meaning they will eventually out-produce shrimp. The more scuds you have in your tank, the less food there will be left for the shrimp.


In freshwater ecosystems, scuds are some of the most reliable invasive species. Some gammarids can withstand lower oxygen concentrations and more extreme temperatures than other organisms.

Also, they’re able to survive in a much wider range of pH levels and salinity levels. Some scuds can even remain out of water for days at a time!

Potential Aggression

Although there isn’t much evidence of scuds attacking or eating shrimp, this doesn’t rule out the possibility, especially when baby shrimp are molting and at their most vulnerable.

As I stated earlier, there are many types of scud species. Contrary to popular belief, not all scuds are herbivores and scavengers.

In fact, some more widespread species have been found to act as predators rather than simply feeders on algae or fallen leaves. Therefore, carnivorous and cannibalistic behavior is actually quite common in the world of scuds.

For example, if you attempt to put Dikerogammarus villosus in a shrimp or fish tank, it will be an absolute disaster. They are called ‘Killer shrimp’ for good reason—they can grow up to 3 cm or 1.2 inches long!

They’re vicious predators that feast on aquatic bugs, leeches, isopods, shrimp, and even small fish like dragonfly larvae and juvenile crayfish.

Do Scuds Pose a Threat to Snails?

In aquariums, scuds are harmful to snails. They compete with other animals for food resources, and they have been known to attack snails and eat their eggs.

Some snails have trap doors that protect them from predators, but not all do. Scuds are often seen as a nuisance to these creatures because they constantly groom and pick up mucus. However, it’s unknown whether or not scuds intentionally kill snails.

Can Scuds Hurt Fish or Their Eggs?

As a general rule, scuds cannot harm your fish. In fact, many aquarists love to watch their fish feast on them!

Scuds’ movements may resemble something that would trigger a hunting instinct in predators- which is why your fish will never be happier than when they’re given the opportunity to chase their natural food source.

However, scuds in your rearing tank can become problematic. This is because scuds are known to take advantage of opportunities to eat or damage fish eggs or fry.

Last Words

Phew! Scuds are definitely a lot more complicated than most people realize. If you’re planning on keeping these creatures in your tank, it’s important that you do your research beforehand to ensure their compatibility with other species. Otherwise, scuds could be the ultimate invader and wreak havoc on your aquarium ecosystem!

Do you have a scud infestation in your aquarium? If so, don’t despair! There are plenty of steps that you can take to keep these pests under control.

I hope these tips have been helpful. If you have any questions or concerns, don’t hesitate to reach out for further advice. Good luck in your battle against scuds!

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