Small scale breeding and catching gammarus pulex - scuds

Freshwater shrimps (scuds) are mostly sold dead and dried as food for fish such as koi carp and are supposedly edible for humans too. They're very common in small streams and can be very abundant if there are no fish in the stream. Although it might be best to avoid lake and sea grown Gammarus because they potentially feed on cyanobacterial algae blooms when in frozen lakes and certain algal blooms can produce the bioaccumulating toxins 'microcystins', fishless lakes can produce LOTS of these shrimp; see this Russian video of 'fishing' for these scuds in a presumably fishless frozen lake or bog: 



Very similar amphipod species are also found in the sea and on the beach feeding off organic matter, here's a video of amphipods on the beach:

I imagine these marine scuds are less likely to accumulate the microcystins as there diet might be more plant matter and bacteria growing on bigger things and detritus, rather than on algal blooms. It might be worth investigating before eating these things though

according to someone's post on caudata.org:

'Here in Minnesota we call freshwater shrimp, Scuds. gammarus. Many different strains. Minnesota is home to several, one in particular, Gammarus lacustris. The largest of the strains. Winter is the best time to harvest them. They are harvested underneath the ice. They are in concentrated numbers under the ice in the spring, due to the abundance of algae growth on the bottom of the ice. Little is written on this strain, in such ways as, intensive culturing. They are thought to be annual breeders and cannibalistic. I also tried to breed them in a more controlled environment, with little success. This was mainly do to time restraints, devoted to my beloved waterchanges. I do raise the Hyalella Azteca with ample success, none do to my expertise This particular strain is very easy to raise. Actually there is nothing to it. Aquarium, green water (phytoplankton), and hang on. These are very prolific and are not seasonal in propagation rulings. I do not know if you can get your hands on these in your country. I would first try to culture the ones you have. If there is no ease in multiplying them, go on to something else. Too much out there to have at our disposal, which in turn allows more time for the beloved water changes of the host that you chose for husbandry.'

Breeding scuds

Lessons so far:
Feeding them slightly too much will kill them. They don't like 'dirty' water; the aquarium they're in had been up and running for a year with a small filter, aquatic moss, pond snails and aquarium lights. I guess that is a requirement to have a tank up and running so that good bacteria populations thrive and tank is in equalibrium (although 2 weeks rather than a year should do it). Feeding them slightly too much killed them. If you keep a regular watch on the tank I think it's possible to predict whether you have overfed the tank or just generally that the water quality has degraded: When the water quality is degraded due to overfeeding, before they start dying off, they all seem to come to the surface as if trying to escape the water. Another sign is that lots of detritus worms might start poking their bodies out of the mulm/aquatic soil substrate or you will see small detritus worms free-swimming in the water possibly due to nitrate or nitrite build up in the substrate. At this point a water change helps and they immediately go back to normal behaviour

They don't really 'like' fine sand; some sites say they enjoy burrowing in the sand, with the fine sand I used I saw none of them burrowing. I think the sand just provided anaerobic conditions for the debris that built up in there and so was bad for the water quality as the wrong kind of bacteria may flourish in those conditions. When the scuds started to die (from over-feeding and possibly debris in the sand) I removed the sand with a siphon and returned the water and scuds to the tank

They like living inside the filter: I have a small, weak impeller filter, after a while I noticed a lot had disappeared and when I went to clean the filter sponge they were all inside the filter I left the filter in there since they can easily make their way out and there's plenty of bacterial food, water movement and oxygen in there. On subsequent checks of the filter there have been fewer scuds in there for whatever reason

They like filter sponge. I often see the babies swimming in and out of a filter sponge I added to the tank. The babies also seem to like the mass of free-floating java moss in there

They like mud. I left some mud in the tank from the ditch I got the scuds from and later on I found lots of babies crawling about in there, I suspect there's lots of food in there that's the right size for the babies whilst other food might be too big. In the wild I've seen the adults love burying themselves/hiding in the fine, light mud/mulm. If it's possible to have mud in the tank without overloading the tank with nutrients or making the water permanently cloudy this might be a good option. Update: I've grown my own mulm substrate (thanks to aquatic snail faeces) for a few months and the water quality I think has been fine, although overfeeding has caused a crash a couple of times I'm not putting this down to the substrate. There was no cloudiness until recently and now, even with big water changes it seems hard to reduce it. A better filter system might solve this. Activated carbon would strip the water of nutrients the scuds need but perhaps something like purigen would work. Either way it's probably not essential to have crystal clear water

In lab conditions... 'We found an optimum temperature for growth of approximately 17°C'
this is from this study:

'From population-level effects to individual response: modelling temperature dependence in Gammarus pulex'

http://jeb.biologists.org/content/214/21/3678

Food they eat:

Cucumber - weighted down with a piece of blue-tac and a toothpick they all congregate on the underside of the cucumber slice
Fish flakes - once the flakes sink to the bottom of the tank
Catfish food (algae wafers) - crumbled up to make them a more manageable size
red pepper (non spicy)
cornmeal (I've not tried cornflour/starch yet)
Possibly spirulina powder although hard to see if they're eating it since it's so smallLentils (I can't remember which ones exactly they eat I think I tried red, green and split peas) they swim around holding the lentil it's amusing to me

A study on how environmental estrogen increases the production rate of Gammarus populations: http://www.ncbi.nlm.nih.gov/pubmed/11833814

https://www.ncbi.nlm.nih.gov/pubmed/26297924

https://www.ncbi.nlm.nih.gov/pubmed/25594120

An article describing how fish populations die out with slight increases in environmental oestrogen in the water: http://news.nationalgeographic.com/news/2007/05/070521-sex-fish.html Perhaps if the shrimp are being cultured as livefood then oestrogen should be used (or not used) accordingly in the Gammarus livefood tank. Higher estrogen might not be good for breeder fish but otherwise it probably doesn't matter. It might be possible to only harvest the bigger (male) scuds to reduce oestrogen in the diet if the culture is supplemented with oestrogen and so a schedule of using oestrogen in the water then having a period without it to re-stabilise the population and oestrogen available to whatever is consuming the shrimp.


Foods that naturally increase the body's estrogen production:

The University of Minnesota notes that foods that help boost estrogen naturally include apples, alfalfa, barley, baker's yeast, beets, cherries, chickpeas, carrots,celery, cucumbers, dates, fennel, oats, olives and olive oil, papaya, peas, plums, pomegranates, potatoes, beans, rhubarb, rice, tomatoes, wheat and yams

Gammarus shrimp produce more offspring during the winter I think so, although better growth would happen at 17C, better population increase might happen at lower temperatures. Moving populations