Neither - it is an amphipod - Order Amphipoda. Also see DD1's comment below.
Bruce, I do not have a local source for them. If I had a local source, I would know what type of weeds were present where the scuds were thriving. I have been buying mine from Wildlife Nurseries Inc, but this year I may get some from Colorado Fisheries. I was trying to establish them in my perch-SMB pond. I got freshwater shrimp to thrive I figured I could get scuds to survive, but not much succes after three tries. I have drained that pond and will convert it to a minnow/shiner and invertebrate pond for stocking supplies. I would like to know the best vegetation for the sucds. Several species are common but the more common and more obvious ones are Gammarus lacustris (22mm) and G. fasciatus (14mm). Crangonyx is another common genus in the US. Hyalella azteca (4-8mm) is widely distributed and real common but not real obvious to the untrained observer.
I think the perch that are "too lazy", will stay eating pellets on a regular basis. I think some swithch back and forth between pellets and natural food based on what is currrently abundant. "Rogue" pellet raised yellow perch revert to eating natural food items. When natual foods are plentiful I think a large percentage of pellet trained fish will go off pellets - these I call rogues. I currently think the more natural foods that are present in a pond the greater the percentage of perch will quite eating pellets and vice versa.
I am still not sure what causes a non-pellet trained and recruited fish to resort to eating pellets on their own. Do some fish have "welfare mentality"?.
