A lot of wrapped blacks sold in tackle shops further south are coming from holland i believe, if frozen these may have been sourced elsewhere in europe, not sure if this is the case but maybe!!
Regarding the staining after using blacks and yellow tails only one thing works really well and that is neat bleach, pour some into your hands and rub thoroughly, use a nail brush to get into the the edges of your nails, the staining turns black instantly and then washes off, hands get very warm from the reaction with the bleach. Stings like a bugger if you have had a busy night unhooking loads of whities, it finds all the little teeth scrapes!!