All,

I took some more careful measurements. One of the things I noticed is
that the current I read needs 30 seconds or so to settle down
sometimes (e.g. it reads a higher current at first and then goes
lower), also the analog and digital meters have their strengths so I
used a combination of the two to get better readings last night.

Boat = Beneteau 393, 39 foot long 14 foot wide, at a slip in salt
water, cable and zinc fish below are off starboard side abreast
cockpit, approx. abrest the propeller. Slip is on the starboard side.
Power boat on my port side, sailboat across the walk on my starboard
side.

Zinc Fish = brand new fish with 25' cable, typical west marine type
product, at a depth of 3 feet

Copper Cable = new 25' 10 gauge copper cable, stranded, with 1/4 inch
exposed to water at a depth of 3 feet.

Boat ground = a 19 foot, 14 gauge cable that runs from the starter
battery upto a stainless steel bolt mounted in cockpit locker for zinc
fish to attach too, brand new, all connections are free of corrosion.

All measurements below are with the black cable on the VOM meters
attached to boat ground. The Analog meter, a small portable, has a
range of 10uA to 250mA. The Digital meter has a range of 1mA to 10A.
Unless otherwise written shore power cord is disconnected.

[1. With minimal power on (Link 20, some lights)]
Copper cable to boat ground = 0.4 mA (e.g. 400uA), 4.5 Ohms, 0.733
volts
Fish to boat ground = -42mA, 0.6 Ohms, -0.127 volts
Cooper cable to fish (black) = 3.5 Ohms, +0.84 volts
Fish to copper cable (black) = 37 Ohms

Interesting !! Is the fish causing this ? Is it harmless ?
Should I consider not connecting the fish to boat ground ?

[2. With All batteries disconnected, everything off accept bilge pump
and Link-20]
Fish to boat ground = -42mA
House Load to boat ground = 30 KOhms (anything better than 1kOhms is
considered acceptable in most books, as evidence of very low
leakage).

[3. With virtually all DC power on (27.5 amps)]
Fish to boat ground = -27mA

[4. With minimal power, shore power connected, and battery charger
running]
Fish to boat gorund = -50mA to -70mA, varies as battery charger cycles
thru charging batteries (it cycles between charging the starter
battery and house battery)

What action should I take ?