Careful, I've heard some bad customs stories. It seems that some
customs people don't know the exact particulars of what can and can't
cross borders. Someone on the bettalist told a horror story of
bringing fish (corys I think) from Britan to USA and the customs guy
couldn't tell the difference between the corys that were OK and some
other species that wasn't. Sigh.

Check with your respective laws, I doubt there's much problem with
daphnia. Be careful about shipping in cold weather though, I'd wait
'till it gets a bit warmer.