Are Anodes needed for fresh water only immersion ?

I just bought a 1991 year old Tohatsu 30hp that was winter prepped and stored in
barn for 15 years. It looks and runs good now but in the location where the anode
is supposed to be there is nothing. I expect the boat will see contact with fresh inland
water only about 125 hours a year and always hauled out and stored on trailer.

Do I even need to be concerned with electrolysis or getting the proper anode ?

BTW, which is the optimum anode for fresh water..... zink, alum, or magnesium ?

Depending on model, the anode is also a trim tab. Yes, you want an anode. The Factory anodes are zinc. What is your actual model/serial?

The model of my engine is M30A3-346B as shown on the affixed engine tag.

Tohatsu USA felt it was sold new around 1991 in a recent conversation.

By the way... Calling the anode a trim tab to me sounds awfully goofy. I feel like if the boat is
drifting off course one way or the other there needs to be a steering correction.

No. The trim tab, which is also a zinc anode, is used to compensate for prop walk and prop torque. That helps negate load on the steering, to make the motor easier to steer -- otherwise, the motor may prefer port to starboard or vice versa. 3C8602171 is the current part number. It attaches with a stainless bolt. MSRP is $13.13.

Anodes are sacrificial, and always a good idea to reduce corrosion of other metals immersed in water. Yes, salt water is much more reactive, but we see a lot of corrosion in the Great Lakes as well. Particularly if you have a battery aboard, or have a metal boat, anodes are a must.

In fresh water, the mag anodes would be preferred, but those weren't made for outboards back 25-30 years ago.

salt water you use zinc or aluminum
fresh water use magnesium
brackish water use aluminum

if you keep the boat on a trailer, use it only in fresh water, and you dont park it in a marina where shore power is available to other boats. you dont NEED an anode... but if you have a place for one on the motor, why not put one there? if in fresh water always, use magnesium for the best protection.