So how is parasite transmission best avoided when using gammarus? If I culture them, would the parasites not be transmitted to subsequent generations?
A little late but anyway...
From what I have read, for the parasite in question to reproduce it needs more than one host species. So, the parasite babies infect the gammarus and alter their behavior by making them swim towards the surface of water (as opposed to hiding in bottom muck or plants) where the scuds are then eaten by waterfowl. Its in the digest tract of the birds that the parasite can complete its life cycle, and the birds poop out more baby parasites that in turn will go on to infect scuds, that will then be eaten by birds, and on and on.
So, if you want to catch wild scuds and begin culturing them, they should be parasite free after the first generation all dies out as long as the culture never comes in contact with ducks that will poop in it. But you will need a bit of patience to wait for that first generation to all die out and only be left with subsequent generations - I have read that a single scud may be able to live for as long as a year.
HJ