Debunking gammarus myths…

When I originally decided to set up a tank for gammarus shrimp (a.k.a. "scuds"), I (naturally) did some research on caring for them and building a successful colony.  In general, the requirements I read about included:

  • Provide cool, well-oxygenated water.
  • Have good filtration.
  • Provide plenty of dark areas (especially under leaf litter).

In addition, I found a couple of notes relating to their feeding:

  • Make sure they have access to plant matter like leaf litter.
  • Feeding processed fish food may or may not be necessary.
  • Depending on who you ask, they may or may not eat live plants.

So… months later, I’ve discovered that some of these “rules” aren’t nearly as important as I was led to believe.  Here’s my attempt to debunk some of the myths I found:

Myth:  Gammarus need cool, well-oxygenated water.

Reality:  It’s true that they don’t need heat, but oxygenation isn’t important.

Check out this video from my YouTube channel:

This is a 5-gallon wastewater bucket in my fishroom.  I was lazy about emptying it, and it was a convenient place to toss the overgrown Nymphaea lily pads from the shrimp tank when I’d trim them out.  A few shrimp apparently hitchhiked on the discarded lily pads, and after several weeks, I realized that they were thriving in the bucket.  In the video, you can see that there’s a film on top of the water — that’s because there is nothing disturbing the water surface.  The film inhibits gas exchange, which would be minimal anyway due to the motionless water, so there’s very little oxygenation happening.  The shrimp don’t seem to care.

Myth:  They need good filtration.

Reality:  Every aquatic animal will do better with filtration, but the shrimp don’t seem to worry about it too much.

Again, I refer you to the video.  There’s no filter in the bucket.  I do occasionally toss plant trimmings into the bucket, but they don’t get enough light to live, so I don’t have an accidental Walstad setup going.  Decaying leaves, mulm in the bottom of the bucket, dead insects, and the occasional bit of fish food (because science!) don’t generate enough ammonia to kill the shrimp.  I even dropped a dead fish in there once, and the shrimp lived through that, too.

Myth:  Shrimp need darkness.

Reality:  Shrimp don’t mind darkness.  They also don’t mind light.

I’ve never observed that my gammarus cared whether they were in the dark or not.  Like any species near the bottom of the food chain, they’ll find hiding places, but they’ll “hide” even in well-light areas of the tank… or bucket.

Feeding gammarus

Not exactly a myth, not exactly not a myth, since feeding instructions vary depending on where you’re getting information.

I can confirm first-hand that they absolutely will eat live plants.  They will completely destroy leaves if there is not enough other food available.  Lily pads appear to be particular favorites (see the photographic evidence below), although this happens less if there is plenty of other food available.

Holey liliesCompletely eaten lily pad

Leaf litter gets chewed up as well.  They definitely appreciate having some dead leaves to snack on.  I can’t tell that they prefer dead leaves over live ones, though.

Oddly, they’ll swarm over dead insects that may be floating in the top of the tank; I dropped a dead beetle in the wastewater bucket, and the shrimp stayed attached to its sides for several days until it either sank into the murky depths or was completely eaten — I’m not sure which.

As far as processed fish foods go, I’ve got a big can of Wardley shrimp pellets that seem to be their favorite food.  They’ll eat almost anything, though, including dried river shrimp, although it takes a while for them to finish off some foods.  I do recommend feeding them something like the shrimp pellets if they’re in a planted tank.  Either that, or introduce a predator to the tank to keep their numbers low.

Bottom line:  what do I recommend?

I do recommend a decent sponge filter.  It’s a good, safe way to provide stable water quality for the shrimp, even though it may not be necessary, strictly speaking.

Skip the heater; they don’t need it.

If you’re keeping them in a planted tank, feed them well or introduce a predator.

If you don’t care about plants in their tank, illuminate the tank with some cheap lighting and toss unwanted plant trimmings from your other tanks into the shrimp tank.

Leaf litter is good if you can guarantee that it’s free of toxins, but I don’t think that it’s necessary, especially if you dump your plant trimmings into the tank.

Have no worries about light levels, oxygenation, pristine water quality, or the other normal considerations that you might have in other tanks… they’ll do just fine.

Photo credit (gammarus closeup): Michal Maňas (User:snek01 on Wikimedia Commons). Photo licensed under CC-by-2.5.