Just read this old study on introduction of gammarus into lakes to raise fish production.. these 2 particular species breed faster and can be predatory in nature.
Both Gmelinoides fasciatus and Gammarus lacustris are omnivorous animals that are able to feed on detritus, plant debris and periphyton, but they prefer to prey on small invertebrates
I think most of us have Gammarus pulex in our tanks, a detrivore that breed slower, but may also exhibit predatory behavior towards young shrimp. All I could find was this: There is mutual predatory behavior between Gammarus pulex and Gammarus duebeni celticus on the newly molted (http://onlinelibrary.wiley.com/doi/1...815.x/abstract
). It only makes sense that they would predate on newly born shrimp.
I can't really tell any of them apart, trying to Google out more pics. Main worried because I have TONS of scuds in my 20L and never see any baby shrimp around. I removed my platies, corydoras habrosus, so all that's left are the scuds and a few CPDs. Previously I thought they were harmless, maybe not so much...