There is a species of ant that farms aphids and actually cares for them on the plant. The ants collect the secretions that the aphids make -- honeydew. It's easy to tell where the aphid infestation is; you just look for the ants running up and down the branch of the gooseberry.

Yes, some of those ants live on our blackcurrant bushes. They're protective little sods - i only have to pick a few blackcurrants and they come and attack my fingers. The aphids don't seem to harm the plant though - the ants keep them under control.

I've never noticed them on our gooseberries though.