Freshwater Amphipod – Gammarus

2008 April 12

 Not really a freshwater shrimp

Last Sunday, it was pretty warm, and S_ suggested that it would be a good day to take Sam down to the stream[1] to turn over some rocks to see what was underneath[2]. So, I grabbed this rock that was in the middle of the stream, turned it over, and found about 20 of these clinging to the bottom:


This was a surprise. I’ve turned over a lot of rocks in streams before, and never seen anything like this. It turned out that the most straightforward way to photograph them was to put some water in the petri dish that I normally use, put three of them in, and just let them swim around. And they did swim around — they zoomed around in circles pretty much without a break. Every now and then, one would stop long enough for a photograph, but then one or both of the others would pile into it and they’d be off again.


Given how much they looked like shrimp, it was pretty obvious that they were some type of crustacean. It was clear that Bug Guide wasn’t going to be any help, because at the time they explicitly excluded fully-aquatic non-insect arthropods (this has changed since 2008 when I first wrote this page, by the way. As of 2013, BugGuide now includes freshwater crustaceans, and also any saltwater crustaceans that are likely to be found walking around on beaches).

S_ did a bit of rummaging around, and found out that they were freshwater amphipods, in the genus Gammarus[3], also commonly known as “scuds”.
They are frequently mistaken for shrimp, but shrimp are a different crustacean order (shrimp are decapods, not amphipods).

For something that lives under rocks and comes out at night, they have reasonably well-developed compound eyes (you should be able to see the individual cells of the compound eyes here)


You can also see the bases of the antennae here. Unlike insects, which have two antennae, crustaceans evidently have four. The function is similar (smell, taste, touch), the crustaceans simply have more of their head appendages devoted to the task.

Gammarus[4] are detrivores. They eat small bits of organic debris – decaying plants, algae, fungus, animals smaller than themselves, each others’ corpses . . . pretty much anything they can get into their mouths. They have a set of legs on their abdomen that never seem to stop moving, they just keep paddling along, sweeping water along the underside of their bodies, and grab anything edible that flows past. They don’t really seem to swim much up in the open water, they are more likely to scoot rapidly along the bottom while lying on their sides. They evidently need well-oxygenated water (which generally means cold water, because cold water dissolves more oxygen than warm water), and do poorly if there are any pollutants present. They are doing really well in our little stream, so I’d say our water is probably pretty unpolluted.

These guys look so very shrimpy, that I keep thinking that it’s too bad they aren’t bigger – about 2 inches long would be big enough to peel and eat. I bet they’d be pretty tasty if they were, say, steamed, peeled, and dipped in melted butter. Mmmm. Butter. Maybe I could selectively breed them to be bigger. A lot bigger.

They are also sharing the stream with a lot of other little aquatic arthropods, I’ll have pictures of one of their neighbors next week.
[1] Just off the NE corner of our house, there is a small year-round spring that produces a continuous stream of water. Technically, this could be considered a “creek”, even though at the points where it has a well-defined channel, it is maybe 6 inches wide and 3 inches deep, and runs maybe 200 feet from the spring to the drainage ditch by the road. It’s too small for fish, but it is a paradise for small aquatic arthropods.

[2] Getting to the creek is much more of an undertaking than it sounds like. Even though it is only about 50 feet from the house, the direct route there involves getting through a barrier of brush and Virginia Creeper vines while descending down a very steep slope with a drop of about 10 feet. At this time of year, there is also still about 3 feet of snow on the slope, because it is protected from direct sunlight and takes a long time to melt. Then, once at the bottom, it is unwise to stand in one spot for very long, because right beside the spring is a patch of very sticky, clayey muck that your feet gradually sink into. It’s a good place to lose boots. It is much easier to get out by following the stream all the way to the road, and then walking up the road back to the house, which is probably 10 times further than the direct route but far easier walking.

[3] Oddly, for these beasts the best sites to find pictures are not pages written by biologists, but rather pages written by fishermen. Gammarus evidently makes very good fish bait, you can buy them commercially. I gather that they are also popular in aquariums, and it looks like dried Gammarus pellets are a good food supplement for pet turtles (it keeps their shells from getting soft).

[4] I keep looking at this name and thinking of “Gamera”, the giant Japanese monster turtle that flies by pulling in its legs and shooting out jets of flame.

30 Responses
  1. April 18, 2008

    What a great blog. I learn things every time I stop by. Thanks for sharing this with us.

  2. garden permalink
    April 26, 2008

    Would you be willing to ship some of these to me? I’ve searched in many creeks and ponds near my house, (SC) and haven’t been able to find any. Many years ago, I had a culture of them that I would raise and feed to my aquarium fish.

  3. April 26, 2008

    Well, I suppose I could try shipping some to you, but I have no idea how well it would work. I’ve never tried mailing live specimens, would they have reasonable odds of surviving if I just put maybe a dozen of them in a closed plastic jar with lots of water, and shipped them regular mail? It’s kind of a long way from here to SC, do you think they’d survive for 4-5 days in the mail?

  4. garden permalink
    April 26, 2008

    I’ve ordered freshwater shrimp through the mail (priority mail) several times. They usually come double-bagged in fish bags. Duct taped double-bagged ziplock bags work too. There’s usually an aquatic plant or something in the bag that they can cling on to.

    Actually, now that I think about it, I had always ordered shrimp when the weather was a bit cooler. It’ll be in the 80s here this week. I don’t think I want to subject the little guys to an unnecessary death. I guess I’ll keep searching streams and lakes. Thank you though.

    I also forgot to mention earlier that I really love the site.

  5. tim permalink
    June 4, 2008

    At this moment, I have about 100 shrimp swimming in front of me. I’ve been raising them as acquarium fish food. I’d caution “garden” against feeding them directly to fish, as they may be a carrier of parasites/disease. It’s best to culture them for a couple months so the parasites (the ones that depend on multiple hosts) die off. I’m trying to selectively breed some to a large size (the largest are nearly a cm), but I’m doubtful if I’d ever get enough to make even a decent shrimp omlette.

  6. June 4, 2008

    Well, 1 cm isn’t half bad, it’s certainly a good start. Maybe in 20 years or so they’ll hit eating size. Do you have any cultivation tips?

  7. tim permalink
    June 4, 2008

    I spent most of my childhood studying my backyard arthropods (grasshoppers in elem school, then spiders in high school). I wish I had documented everything I found, but alas, I didn’t. I love the pics and commentary.

    Back on topic, whenever I siphon off the water from my aquarium, I just let it sit in its bucket for about 10 minutes. I pour out the mostly clear stuff on top, and the detritus on bottom (fish and snail poop, decaying plants) goes into various containers I have around the house which house the gammarus shrimp. Most of them are clear plastic containers to make easier collection/observation, but also to give some photosynthesis to whatever algae are in the water (backup food for the shrimp). I also have float duckweed (skimmed off from my aquariums) in these containers as an additional source of backup food. Using this method, I’ve never had to actually feed the shrimp. They are all indoors, but next to a west facing window. The only time I experienced a die-off was when I put some in a used plastic water bottle, but capped it for a few days. The lack of oxygen sufficated them all. But generally, they’re relatively hardy creatures, tolerating even a hot summer afternoon sun.

  8. Roland permalink
    August 29, 2008

    Finding alot of interesting information. I would like to culture scuds for the science class. Have access to lots in the lake behing the school.Could I feed them boiled lettuce because this is what I feed some tadpoles and worked well. They eat alot of lettuce. Would appreciate some information. Thank alot.


  9. August 30, 2008

    Boiled lettuce sounds close enough to what the commenter above was using, that it should work. Since tadpoles are detrivores too, I would expect than anything that worked for raising tadpoles should be fine for raising scuds too, but I haven’t tried it myself. Please let us know how it comes out!

  10. Hayduke permalink
    December 21, 2008

    I just collected some plants for an aquarium but saved a few along with a lot of hair algae for a ten gallon tank to see what critters I might have collected along with. The plants and pond scum were collected about a quarter mile from some springs feeding a stream. There were some mosquito fish living in the stream.

    There are large amounts of daphnia, scuds, isopods, hydra, insect larvae, snails, mites and all sorts of other things that I’ve found in the tank now. I wonder how succesfully the amphipods will survive in the tank as it is? I’m considering moving some of the scuds to another container for cultivation… or maybe turning this 10 gallon into a tank for them.

    I really enjoyed this article you wrote. You have a very nice website and I am about to browse the rest of it.

  11. CAB permalink
    December 22, 2008

    Last winter I collected a few amphipods from a stock pond in Texas, and put them in a jar next to an east facing window. (At the same time, I also gathered some water plants and grabbed a handful of pond mud to complete their new environment.) They are still going strong 9 months later, slowly increasing in population. At first I did some partial water changes, but even this seems unnecessary.

    Just out of curiosity, I put about a 1/4 inch of this pond mud in a 6oz.jar of pond water, sealed it, and put it next to the first batch of amphipods. In a few days, plants started emerging, and a few days later, so did amphipods. This jar has remained sealed since July. The only input has been indirect sunlight. It still has a small population of amphipods. The water is crystal clear. Biosphere 4.

  12. February 2, 2009


    Thanks for the blog!
    I have to say that seawater amphipods Gammarus setosus really looks like this ones, and that feeding behaviour is pretty the same. They even eat freswater worms.

    I have a question, maybe if someone know better than me: What would the freshwater amphipod Pallaseopsis quadrispinosa eat in normal conditions? I am feeding them now with tetramin but I would like to know if they would eat algae or other smaller organisms! Particularly, a smaller organisms would be great to know.

  13. March 18, 2009

    Our company supply various of aquarium fish feed.
    Every year,export about 200tons gammarus.

  14. Jim Crawford permalink
    April 17, 2010

    From the dates on here I suspect I won’t get an answer…but here goes:
    Can anyone tell me where I can buy LIVE Gammarus in bulk? I have a 30 acre pond with trout and bass and would like to stock it with Gammarus for feed.


    Jim Crawford

  15. April 18, 2010

    Before trying to buy some, if possible I’d suggest finding a small stream in your neighborhood (preferably one too small for fish to live in), and turn over some rocks to see if you can find some underneath. That way, any Gammarus that you stock in the pond will already be adapted to your particular climate.

    If you have no such streams in your area, I did turn up at least one place where you can buy live gammarus in something resembling bulk (although, I’d like to note that I’ve never had any dealings with these people, so I have no idea how good they are):

    They do like to have rocks and other structure to hide under, so if your pond doesn’t have such structure already, you might want to add some. Otherwise, I’m afraid your trout and bass will devour them instantly before they can establish a long-term population.

  16. katana permalink
    June 12, 2010

    hi i am 11 and i live in edmonton and i have a pond behind my house and i have like 30 of those things she just swim in circles and i also put leeches in there too and they clen my tank for me and the leeches dont bother the shrimp thingy

  17. June 13, 2010

    Katana: That sounds like an interesting aquarium to watch. I always liked the way that leeches walk along by grabbing onto things with their suckers and flipping end over end. Feeding them might be an issue, though . . .

  18. Sarah permalink
    February 16, 2011

    I found these little buggers in my African Cichlid tank and I didnt put them there…….. 🙂

  19. February 17, 2011

    I’ve heard of these turning up in odd places, like pet water bowls, and I really have no idea how they do it. Well, at any rate, I’m sure your fish will like them.

  20. kelly permalink
    November 8, 2011

    great article & pix!!
    I used to have a tropical fish store (& have been creek-sloggin’ my whole life), so am real familiar with gammarus.
    In the store, they would often turn up with live plants. Don’t often see plants in African cichlid tanks, but they can also hang up on nets, rocks, etc, particularly the little ones. btw, in addition to being good food for larger fish, they make great scavengers for fry tanks; they’ll scrounge any excess non-live food without snacking on your baby fish. I’ve used the fry/gammarus combo as a ‘grow out’ tank for both fish & continuing gammarus culturing.
    i’m with Tim re; possibility of parasites, tho the ones that came with the aquarium plants in the store never appeared to cause problems to the fish I fed ’em to, & heaven knows aq plant suppliers don’t grow their plants in sterile conditions!
    You can buy live ‘starter’ cultures at both Niles Biological & Carolina Biological. I’ve always had good results w/CB; have never ordered from Niles, so dunno about them other than they seem to have a very foggy grip on shipping charges.
    happy scudding!

  21. November 9, 2011

    Thanks, Kelly!

    It might be time for me to get new pictures and update this page, including all the new information people have given in the comments. Also, I see that BugGuide has changed their policy; they still don’t have marine crustaceans, but they have decided to include freshwater crustaceans, including Gammarids.

    Oh, and Carolina Biological’s website is here:

  22. kelly permalink
    November 9, 2011

    Ted, thanks for adding the CB site addy, oversight on my part. I just ordered some more gammarus from them, having lost all my cultures from a recent cross country move. It occurred to me to add that some might have trouble culturing them if they have copper in their water…I’ve found the hard way that the water in the house where I now live (Durham, NC) has enough that all my fw shrimp (crystal reds, cherries, tigers) have croaked within 24 hours of arrival….this despite a big carbon/particulate filter system in the fish room (& I use Amquel too, as we have chloramines). I fear the scuds may be sensitive to it also, so before I get my gams I’m gonna get a chelating agent such as Novaqua Plus (it claims to chelate metals). anybody got any other recommendations for copper removal? I know Polyfilter does a good job but i’m planning on putting the gams in least 5 different tanks, most 55+ gallons, so it’d get mighty $$$$$!

  23. kelly permalink
    November 12, 2011

    Me again; mayhaps I goofed; ran across a UK paper (“The Trophic Ecology of Freshwater Gammarus spp. (Crustacea:Amphipoda): Problems and Perspectives Concerning the Functional Feeding Group Concept”) saying Gams can be predatory/carnivorous -said mostly cannibalistic, but may prey on wounded fish or fry.

    On the other hand, my invert bible (R Pennak’s “Freshwater Invertebrates of the United States”) sez “Only rarely do they attack & feed on living animals, but freshly killed animals are consumed readily.” i.e. back to detritivores. Maybe British Gams are just meaner? ;-). Pennak also says they serve as intermediate hosts for “a wide variety of parasites” of fishes, amphibians, etc.

    btw, they are tough little buggers: newly arrived Gams from CaroBio do just fine if you flip their open plastic jar off the countertop & scatter them hell-to-breakfast across the kitchen floor, then spend fifteen minutes carefully picking up each one & putting it back into water. However, I don’t recommend it; it ranks very low on the Fun Pastime scale.

    Copper may not be the problem I was having; all the Gams died in at least one planted tank & I treated it with a chelating agent before adding them. Doing ok so far in the small (5g) planted tank & the bare plastic ‘shoebox’ I set up just for them… with the same water source & same chelating agent. Argh.

  24. May 13, 2012

    Great site! I tripped over it through googling “amphipod”. I do some informal pond programs at a local farm and have been trying to id the wriggly things we scoop up in nets. While my cousin is a PhD bearing entomologist, i am a serious amateur naturalist with a kayak and a digital camera (not bad tools for exploring Planet Water). Some pics here:

    Found some amphipods attached in pairs… hmmmm, perhaps like crab “doublers” (mating).

  25. Faezeh permalink
    July 16, 2012

    Thanks, great website.
    Actually i have a problem with some small insects in my room. They look like crustaceans (tiny shrimps) but smaller, maybe 2 centimeters. They walk fast, have many legs and they have a unique tail. Their tail has 3 parts in 3 directions. The tail is always in touch with the ground. They look pretty much prehistoric. I like them and i don’t mind seeing them around 🙂 Once i fed them biscuits and they liked it. I just wanna know what species they are. Thanks.

  26. July 16, 2012


    From your description, I’d say they are probably silverfish or firebrats. There are pictures at this site:

    These are pretty widespread, but for some reason we don’t seem to have any around our house. Probably because they need moisture, and our house gets pretty dry in the winter.

  27. Faezeh permalink
    July 16, 2012

    That’s right. Nice pics.
    So they’re silverfish. Weird name.
    Thanks a lot for ur help.

  28. kelly howard permalink
    August 6, 2012

    Hi Faezeh,
    I’d like silverfish too –they are pretty cool looking– if it weren’t for their dining habits. They eat books; glue, bindings, paper, etc…also fabrics, paint, leather sometimes…can go a year without food…in other words, absolutely everything you don’t want ’em to eat. You’re usually ok if you live in a very dry climate (& don’t have too many aquariums), but the little buggers are SO difficult (impossible?) to eradicate if they do get established in your stuff. For myself, i wouldn’t encourage the little beasts. Sorry if I rained on your parade.

  29. Gerry permalink
    July 9, 2013

    Hi Kelly,
    Why not try this. Instead of trying to remove metals and other things from your water, start with clean water. I like to start any new colony by using distilled water to start. It is sold really cheap in large bottles from any large department store. It is sold for use in humidifiers, irons and other appliances that require water that will leave no residue. It is pure H2O.
    If I collect gammarus in the wild for example, I can use a small amout of their pond or creek water that contains detritus and micro organisms to ‘seed’ the pure water at home.
    For gammarus, and freshwater shrimp I recommend adding calcium to the distilled water environment because they do well in calcium rich water.
    There are many calcium products on the market and many ways to add calcium.
    I can also be as easy as adding a sea shell or two that will buffer and slowly dissolve from the weak acidity that is created in the tank from bio decay.

  30. kelly permalink
    July 10, 2013

    Hi Gerry,
    Thank you for the input. I suppose it’s dumb, but when we had the whole RO setup in place it seemed somehow…wrong to buy jugs of bottled water for the live food cultures. Besides, I also had 3 planted tanks, 40 & 55 gallon, with varieties of shrimpy shrimp – cherry shrimp, Japonica (algae eating), etc & didn’t want to buy that much on top of running the RO for the other fishtanks. T’other reason I was hoping to suss out what was in the water –or at least how to get it out– because the whatever-it-was was making ME sick.
    Anyhoo, you’re right, it is easy to make a ‘custom-blend’ water from bottled distilled (or RO) base. I breed several varieties of fish in wildly varying water chemistries, & it’s sorta fun to make up the blends, especially once you realize you don’t have to buy the expensive salt blends & bufferers they sell at stores…a little baking soda, epsom salts, water softener potassium chloride…ta heck with that $10 bottle of GENYOOWINE AFRICAN RIFT LAKE SALT BLEND and the $12 bottle of SPESHUL AFRICAN RIFT LAKE BUFFER HIGH pH. Or whatever. Heh heh.
    Have fun with water!

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