Scuds In Aquarium (What are they and should I remove them?)


Scuds In Aquarium (What Are They and Should I Remove Them)

If you have Scuds in your aquarium, there are a few things you will need to know about them before you decide if they are going to be a problem for you.

Gammarus shrimp better known as Scuds are generally harmless and can be considered excellent live food. Many fish love to eat them but if you keep shrimp in your fish tank, Scuds can be a problem. Scuds attack shrimp when molted from their hard protective shell, and they will feed on baby shrimp.

What Are Aquarium Scuds

Scuds are freshwater amphipods described as small bottom-dwelling crustaceans found in freshwater streams, rivers, ponds, lakes, and swamps; in fact, they are so versatile that you will find them almost anywhere.

Scientifically called “Amphipoda,” they are freshwater shrimp, also known as side-swimmers and more commonly Scuds. 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.

The size of a Scud can vary with newborns starting at around 1mm and fully grown adults ranging from 3mm-8mm in length. The growth cycle of a Gammarus Shrimp is quite complex as it will shed around once every 5 days whilst going through 9 different life cycles.

A scud will usually live for around a year and can live for up to 2 years depending on their living conditions. Colder water is tolerable for Gammarus shrimp, which will slow their life cycle down, extending their lifespan, although they will not survive in temperatures below freezing.

Scuds are usually transparent in appearance, although you may notice some green due to the visibility and function of their digestive tract. Scuds may also have a slightly brown appearance to help them blend into their environment and hide from predatory fish.

If you have Scuds in your fish tank, they will breed very quickly and become a problematic infestation if your tank is not specifically breeding them.

Benefits And Drawbacks Of Scuds In An Aquarium

Depending on your aquarium setup, having Scuds suddenly show up may or may not be an issue for you.

Below is a table showing some of the benefits and drawbacks of having scuds in your aquarium.

Impacted Area of Aquarium Benefits of Scuds Drawbacks 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.
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.
Some of the main benefits and drawbacks of Scuds in your aquarium

How Do You Get Scuds In Your Aquarium

Commonly found in freshwater aquariums, Scuds are usually introduced into your freshwater tank when adding new plants. Baby scuds can hide, unseen within plants, and especially moss which they love to eat, and when added to your aquarium, they will start to breed.

Usually, Scuds will bury themselves deep into the gravel at the base of your aquarium, where they will hide from other fish. Once their numbers grow, which is often quite rapidly, you will start to notice them.

Like many scavengers, when there is food to eat, you will notice large numbers of Scuds crowding over it, and if you have moss planted in your tank, you will often find them here in larger numbers until there is very little moss left.

What Do Scuds Eat

Whether you want them in your tank or not, it is worthwhile knowing what Scuds eat.

Scuds are omnivores, so they will eat pretty much anything they find. As scavengers, the easier the meal, the better and they will clear any waste left in your aquarium. Scuds will eat decaying plant matter, algae, live plants, and rotting fish food, micro-organisms, small live fish or fish fry, and much more.

Because of a Scud’s broad appetite, they can be more of a pest in an aquarium setting. Many aquarists like to introduce moss into their tank and as Scuds eat plants, it will be disheartening to find that moss is a favorite.

Scuds Love To Eat Moss
Scuds Love To Eat Moss Like This Mini Pearl Moss

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

Shrimps or tiny shrimp young are also a target for Scuds. When adult shrimps go through a shedding cycle, it leaves their soft flesh exposed to the Scuds, and they will latch on for their next meal. Scuds are generally not ideal if you enjoy shrimp keeping.

Larger fish are good at keeping Scuds at bay as they are a tasty treat, although young fish and tiny shrimp will also be a target to larger fish, so this is not the best solution to stop Scuds.

Are Scuds Harmful

Scuds are so small that you would be excused for thinking they are completely harmless.

Most aquarists that deal with scuds will be using them as aquarium fish food. In fact, many people will breed scuds for this very purpose, and they are generally considered harmless; however, these freshwater amphipods are great at hiding out in a tank, and if they evade other fish, they can very quickly build up their numbers which are when they can start to become harmful.

As discussed above, the main threat from Scuds is what they eat. If food is scarce or their numbers are very high, they won’t think twice about attacking smaller fish in your tank or eating their way through your nicely planted tank.

It’s great when these freshwater amphipods eat algae, decaying plants, and other waste products, but a shame that a larger Scud population can be aggressive to smaller fish and are so good at killing plants.

How To Get Rid Of Scuds In An Aquarium

If your Scud problem is giving you concerns, there are several ways that you may rid your tank of these pests.

There are quite a few methods to get rid of scuds from your aquarium, although none of them are bullet-proof. The ideas I will put forward, are either tested by myself or are the tried and tested methods of the experts. (Disclaimer: All methods are for informational purposes and should be researched in detail before trying them as I will not be held responsible for any damage sustained to your tank or its contents when using these methods).

How To Remove Aquarium Scuds
How to remove aquarium scuds.

Catch Them And Remove Them

You can attempt to catch scuds with a net but probably won’t be very successful as these freshwater amphipods are fast, generally quite shy, and are great at hiding. They will often bury themselves deep in the substrate at the base of your tank.

Some people have more success with a turkey baster. The benefit of using a turkey baster over a net is that you can suck the Scuds up.

Another method that I heard about and have tried for myself is to leave some bait for them at the bottom of the tank, and as the Scuds attach to it, remove the bait with them still attached.

An example is to boil some carrot or other food that attracts them. When soft enough, you can poke a skewer or similar through and then leave it at the bottom of your tank. Wait for several hours, and then check the carrot or whatever bait you have used.

A large portion of the Scuds in your tank should be feeding on the bait at this point, and you can usually remove the bait quite easily whilst the Scuds are attached, provided you use slow movements and don’t bump anything. Once removed, you can rinse the bait off and put it back in your tank.

You can repeat the above process repeatedly until you find only a few of the pesky blighters feeding, and you will dramatically reduce the number of Scuds in your tank.

Using the baiting process, you will find much more success if you keep the light off in your tank. Although Scuds are quite timid, provided they are not spooked, they will hang on to the bait while you remove it from the tank.

Baiting Scuds will not completely remove them from your tank, but it will heavily reduce their numbers until they begin to breed again.

Cleaning Your Tank, Plants And Gravel

Cleaning your tank will help reduce the number of Scuds in your tank, although it will be tough to eradicate them completely.

To clean your tank effectively, you will need to thoroughly vacuum the gravel or whatever substrate is covering the base of your tank as these freshwater amphipods will bury themselves and be difficult to find. Even when you feel you have given your gravel a thorough going over, you may be disappointed to find out that you have missed some.

Scuds will hide in plants and moss, so you will need to remove these from your tank and rinse them as much as possible. Some would suggest a bleach dip and then rinse thoroughly, but you will need to take care with delicate plants that may not take kindly to bleach.

Check your filter, clean the sponges in hot water, and consider a bleach dip for these as Scuds may feed off the waste that your filter has trapped. Make sure to thoroughly rinse off any bleach before returning to the tank.

Check all areas where you feel these pests may be hiding, and remember to think about where baby Scuds may hide. The Gammarus shrimp does not lay eggs, so you don’t need to worry about hunting them down, but baby Scuds are very difficult to see at only 1 millimeter in length.

Aquarium Gravel Vacuum Cleaner
Use a gravel vacuum and thoroughly work through all sand and gravel inch by inch as Scuds are excellent at hiding.

Increase CO2 Levels In Your Tank

Increasing CO2 levels in an aquarium is a method that has worked for many to kill Scuds. As these little shrimps need oxygen to breathe like everything else in your tank, it will suffocate them if you crank up the CO2 levels.

You will need a spare tank to perform this simple little trick as it will not only kill Scuds but will kill fish as well. When moving your fish to the spare aquarium, make sure it has been cycled, and the water levels are within suitable parameters. Your fish will only need to be in the temporary tank for around an hour, so it will be easier to transfer some water from the main tank.

When transferring both water and fish from the main fish tank, take extra care not to transfer any Scuds along the way, or they will evade the next step of treatment.

The easiest way to dramatically raise CO2 levels in your tank enough to suffocate the Scuds is to pour around 1/2 to 1 liter of carbonated water into the tank. Make sure to use seltzer water with no additives. Soda water or tonic water will not do as it will contaminate the water.

During the daytime, plants feed off CO2 and only feed off oxygen at night, so provided the light is sufficient, your live plants should be fine during this process.

Once you have added the carbonated water, CO2 levels will skyrocket almost instantly and completely starve the tank of dissolved oxygen. Over a period of around 45 minutes to an hour, all Scuds within your aquarium should suffocate.

Before returning your fish to the main tank, it would be wise to check the oxygen levels, which should by now have returned to normal. Create some bubbles at the surface or use other methods to encourage oxygen to enter the water. Return your fish when it is suitable to do so and consider adding fresh water to replace the water sued in the temporary tank.

Along with the baiting method described earlier, this method has worked for me several times, and I continue to use it. On each occasion that I have raised CO2 levels, I have completely eradicated my tank of Scuds with no reappearance over very long periods.

Using Extreme Cold

Some aquarists struggling with Scud infestations have suggested removing all substrate, filters, plants, etc., from the tank, bringing them down to very low temperatures, and potentially freezing them. Personally, I don’t see how this can be effective as you will have to deconstruct your aquarium set up completely, and your plants probably wouldn’t survive freezing.

I would expect your Scuds to die by using this process, but with the simpler methods I have already listed, this method seems like very hard work, which may cause more harm than good.

Add larger fish To Feed On Your Scuds

The final method I will suggest is fairly self-explanatory. As I mentioned at the beginning of this article, Scuds do make good live fish food, and if you add the right aquarium fish and in the right numbers, they will easily keep on top of these potential pests.

As a farmer relies on his cattle and horses to keep his grass down, you can rely on your own fish to keep the Scuds down to a manageable level, but this is only a solution if you do not keep small fish or shrimps in your tank or if you enjoy breeding as the larger fish will inevitably feast on these as well as the Scuds.

Wrapping It Up

If you have Scuds in your aquarium, I hope now that you have read this article, you have a better understanding of what Scuds are, the benefits and drawbacks of having them in your aquarium, and how to remove Scuds from your aquarium. Hopefully, this article can help you to make the best decisions that will best suit your needs.

Jon O'Connell

I have kept both marine and freshwater fish and set up almost 100 aquariums. Happy to share my knowledge and experience to help others enjoy keeping healthy and happy fish.

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