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Recently, I posted a thread in the Invertebrates forum about cultivating Gammarus pulex freshwater shrimps, which I intended to breed to provide food for my assorted fishes.

Well, after a meeting with my fellow entomologists and other invertebrate zoologists on 21st February, I made a discovery. The shrimps that I am cultivating may, in actual fact, be something other than Gammarus pulex!

I was alerted to the possibility that the shrimps I found in my live food may in fact be an alien introduction to the UK in the form of the North American Crangonyx pseudogracilis, an amphipod that superficially resembles Gammarus, but possesses certain key differences. Most notably, Crangonyx psuedogracilis remains a smaller size than Gammarus pulex, and even adults are likely to be considered fine fish food by a wide variety of aquarium fish species.

However, I was told that there was another reason for aquarists to consider cultivating these shrimps. Their food, apparently, includes Spirogyra and related thread algae - including the 'blanket weed' so detested in ponds!

Now, if this information I have been supplied is indeed correct (and I have every reason to be confident in the provenance of the information, coming as it did from a professional biologist specialising in aquatic invertebrates) then this shrimp would seem to be a 'must have' for anyone with a blanket weed problem to overcome!

So, not only will Crangonyx pseudogracilis be a useful species to cultivate as fish food for the inmates of a tropical aquarium, but it will also be a valuable ally in any battle against thread algae! It will feed on other detrital matter too (and I am told that TetraMin fish food will keep it happily alive in an aquarium for some time) but if let loose in an environment where algae is a problem, these little shrimps are apparently an excellent natural control for some of the more troublesome algal species, including algae that fishes won't touch.

So, hunt down this little shrimp today, and harness it for two reasons - fish food and an algal controller!


Panda Catfish fan and keeper/breeder since Christmas 2002

i have a pond that come summer time is infested with thread algae but i have a couple of questions

1)how low a temp can it survive?

2)i have a very large pond with many rocks, plants and fish do u think that they would survive atleast long enough to fix my problem?

3)where can i get them?

They've become established in water bodies not far from my home, so they're capable of surviving a British winter complete with frosts and ponds icing over. Since they're allegedly a North American native, they should be obtainable from ponds just about anywhere in the USA. Do a Google search on the scientific name listed above and get some images so you know what to look for. Generally they're around 5 mm long or so, and have a peculiar walking action that I can only describe as being 'half darting, half scuttling' ... it that makes sense!

Also, they tend to be fairly dark in appearance, with a gunmetal-bluish lustre under certain lighting conditions.

Mine have promptly disappeared into the maze of Java Moss in the quarantine tank, and I suspect I won't know if they've bred successfully until I see small swarms of them out in the gravel. How long I'll have to wait for that to happen is anyone's guess ...

As for sticking them in an established pond with fishes present, best thing to do is make sure you have LOTS of them so that if the fishes eat some, there'll be enough left over to go to ground and start a breedng colony.



Panda Catfish fan and keeper/breeder since Christmas 2002

Do you know if they will eat BB algae? Mine is driving me nutz I have a phosphate problem and have been cutting the feedings and increasing the water change interval but it persists even when the conditions have improved significantly (this is my daughters tank and she is responsable for feeding the fish.) I have enough waterways around here that I am sure to be able to find them somewhere!

oh, iv' got those around here too (makes a note to not let in the 20 long) but i have caught a few and kept them with darters...they were gone in a week lol, but the area there they were living, there were large ammounts of brown algae, but, there were large ammounts of the shrimp in the area too, and also (lol) the water was 7inches deep at the deepest point, the water was around 85F and it was a pool etched in slate, there are quite a few of these pools, and at certin times of the year the river floods it out, it is also where the johney darter loves to spawn...but thats going off topic lol

Hmm. Will have to check and experiment to see if they eat black brush algae. If they do, then once again, a new ally in the battle against nuisance algae ...


Panda Catfish fan and keeper/breeder since Christmas 2002

ive tried googling it and i get nothing

Did you Google on the taxonomic name? You should have obtained quite a few results if you did!


Panda Catfish fan and keeper/breeder since Christmas 2002

i copied and pasted the scientific name and either nothing comes up in either the images or web or it askes if i want to respell it and if i do nothing comes up! otherwise i get a bunch of useless unrelated information

Just did the same, here's the first page I got ...

Google search


Panda Catfish fan and keeper/breeder since Christmas 2002

ohhhh, u use google.uk while i use google.us so i get different web pages

Except of course if people start using these things in ponds regularly , the young will probably escape into local watercourses and that might be very bad competition for our local fauna, including our own increasingly rare species of freshwater shrimp and crayfish.

Actually, Crangonyx pseudogracilis is already established in many bodies of water in the UK, and seems, for once, to be occupying a niche not occupied by native species. I have this on good authority from my colleague in the Entomology Society, who is a specialist in aquatic invertebrate fauna.

Indeed, during our Society's Annual Exhibition (4th March 2006), he brought a big tub with him to represent a sample of a typical local pond, and it contained both Gammarus and Crangonyx living side by side.

Furthermore, Crangonyx seems to be providing a number of UK freshwater fishes with an additional food source. Indeed, productivity of fishing ponds with respect to certain fish species has been cited as increasing when Crangonyx becomes established in the pond. It's lso been cited as one of the few beneficial alien introductions into trout and salmon fisheries, providing the young of these species with a food source that increases their growth rate. While the track record of most alien introductions is a less than happy one, Crangonyx shrimps seem to be an exception. Add to this that it is also cited by my colleague as feeding upon the various filamentous algae species that comprise blanket weed in Goldfish and Koi ponds, and this little shrimp would seem to have a LOT in its favour!


Panda Catfish fan and keeper/breeder since Christmas 2002

where can i find it in the uk and how can i build build up a colony out of my tank (in a jar) eg what do i feed them temp ect ect


Dont feel bad I confuse myself too
everyone loves the almighty spork queen