Freshwater Scuds: The Ultimate Algae Eaters?

Algae is the bane of most freshwater aquarium keepers. We've all had it at some point and many of us continue to struggle with one for or another for long periods of time. No doubt algae has been the reason some have gotten out of the hobby entirely. In my case, I've had to deal with hair algae, staghorn algae, and black beard algae.

I've had success controlling staghorn algae with Seachem's Excel, but I'd rather not have to use such chemicals all of the time. I've been able to knock out hair algae using API's Algaefix, which is harmful to shrimp so not a perfect solution. As for black beard algae, I've found nothing more effective than hydrogen peroxide, but I've never been able to eliminate it entirely and who wants to do treatments every day?

Enter the freshwater scud. These little guys sit at the bottom of the food chain and eat decaying plant matter, left over fish food, and algae. In fact, some testing suggests that if given a healthy plant with algae, they will eat the algae and ignore the leaf. Need proof? Take a look at this before and after shot of an anubias leaf I left in a container of 50 or so scuds for 24+ hours.

Anubias Leaf Covered With AlgaeAnubias Leaf Covered With Algae
Anubias Leaf After Scud CleaningAnubias Leaf After Scud “Cleaning”
BBA in Bottle Cap: Before and 24 Hours After Introducing Scuds

Some other things I've tested:

  1. Scuds seem to be unharmed by Seachem Excel dosed up to 1.75x the standard dose. I haven't tested higher amounts so they may be able to tolerate more.
  2. The scuds cleaned off algae from Lobelia Cardinals “Dwarf” without harming the leaves. I was curious about this because these leaves are sofware than those of the Anubias in the above photos.
  3. The scuds had no problem eating the algae off of wood. Once the algae was gone, the scuds moved on.
  4. Scuds will eat the “leaves” of java moss leaving the stems behind. They eat it slowly though so it's possible the moss will grow fast enough to stay ahead of them.
  5. The overnight temperature that I've confirmed scuds can handle is 2 degrees celsius.

These are things I've read about scuds that I haven't yet verified for myself.

  1. Pygmy Sunfish are good fish for keeping a scud population in check.
  2. There doesn't seem to be a way to kill scuds that won't also kill fish and shrimp. However, some claim that using seltzer water (equivalent to a high dose of CO2) will kill scuds while not killing plants. This sounds promising since it'd be safer than using chemicals that might remain in the tank.

My hope is that I can introduce these scuds directly to my planted aquariums. However, I'm trying to find answers to the following first:

  1. Will the scud population control itself based on the amount of food available? Will the fish keep the scud numbers in check?
  2. Do scuds “prefer” certain foods over others i.e. will they eat algae and decaying plant matter first? Are there some live plants that they can't resist? There are reports that scuds will eat moss.
  3. Do scuds attack young, adult, or moulting shrimp?
  4. If needed, is there any way to eliminate scuds entirely from an aquarium?
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3 Comments

  1. Marios - what a great study of scuds. And I so appreciate the photos and details. I know this article is old yet I'm compelled to write having found it. I have a scud and snail tank for growing food for my various fish. They are fascinating little guys.

    My experience is that the population will not grow if food is insufficient. However, in a tank with fish and plants, it is unlikely that food will ever be insufficient - they will eat from the filter and between the gravel and in the nooks of the plants, finding anything they consider edible, which is a lot. If scud are added to a tank with fish, I think it is likely that the fish will eventually decimate the population unless the scuds find their way into the filter and begin reproducing there or any other place a fish literally can not swim into. I haven't tried it so I can't give any examples - just anecdotal by the way my fish scour the tank looking for them.

    The only tank of mine that has scuds and fish long term is a no tech 1 gallon fish vase with gravel capped soil that is fully planted and has been up for less than a year with only endler fish: I believe the endlers were unable to eat the largest of the scuds which have reproduced and the endlers are eating the young before they can then reproduce. My theory is that the endlers will eat all scuds that they can fit in their mouths and the scuds that are too large will die and no scuds will be left reproducing resulting in no scuds in the tank. The project will conclude when I can not find any scuds in the tank for 2 months or by 12/31/19 whichever comes first! By the way, the scuds I have are wild caught from a local river in VA and some of them are a beautiful dark blue.

    Would love to hear any news of scuds since the original post if you have any additional thoughts or experience. Sometimes we don't think to repost until someone asks for an update - and I'm sure that for every one that says great job and thanks for writing, there are many many more who read and don't comment and still appreciate it. So great job and thanks for writing about scuds Mario!

    • Thanks for sharing your experiences with scuds. I'm leaning towards the idea that they're a good addition to an aquarium since their population will be kept in check if there are fish that will go to the bottom and hunt them.

      My first bit of news is that while scuds will eat BBA, they don't seem to be good at seeking it out. That is, unless the BBA is at the bottom of the tank, the scuds won't find it and eat it. A few times I've put in leaves with BBA and if it's in the middle of the water column or at the surface, it goes untouched.

      Also, I've exposed 20+ plants to scuds along with 4 or so mosses. It doesn't look like scuds ate any of the plants or moss to an extent that it was noticeable.

      • I just put Java fern in my freshwater tank this morning and this evening I find a few scuds on the plants. I wish I could get the scuds down to a controlled population. Help.

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