Don't worry if you don't have any ready-made as it's super easy to make your own! There are no exact measurements for this. Just eyeball it and go with whatever looks right.
All you need are these 4 things:
Mayo, English Mustard, Lemon Juice, and Pickles
Chop the pickles up into itty-bitty pieces. I usually slice into rounds, then cut the rounds with 4 cuts (2 in each direction) so that you have 9 little chunks from each circle. Does that make sense? Whatever... just chop them up small.
Mix the pickle bits, as well as any juice they made while you were chopping, with some mayo.
Squeeze some lemon juice in and mix it up.
Add a little squirt of mustard and mix again. If anything looks wrong, tweak the mix until you're happy.
Add it on your fish and enjoy!