On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thank,