@ bullgoose - yes they are fine, i have seen people keep them on gravel, sand. i am keeping my cherry shrimp on some fertile soil style substrate which they seem to love, i personally don't know much about shrimp but from what i see they are not like cory's (who filter sand through there gills, this is why cory's are best on sand) and shrimp don't do this so i cant see why they can not be kept on gravel, also they are VERY good algae cleaners from my experience and yes sadly will get eaten by most fish i am keeping mine on there own in a separate tank with a just a few snails
@Arcticfox1977 - YES omg YES, i stated of with around 12 i now have 20, in a little as a month from when i bought the original 12, give it a year and probably have 100 of these guys, they will breed rapidly and quickly but it also depends on what type of shrimp you get i guess and if the conditions are good for them