I have a fleet of 4 ships fishing around the Port of Seaglory & all of their cargo holds are currently 25/60. My question is how is profit earned as there are no price quotes, like in a market? When all of each ship's holds are full, is it automatic that each ship return to the harbor & load their fish count into the warehouse?

If you are selling it to the market, the money earned is the current price of the food in the market of that port.

Eventually if you stick with Fishing.. build up your warehouse and choose the option to store your food there. Then use the voodoo Potato Party to earn bigger pay days.

As the ships are full, they'll go back to port and sell the fish or store it in warehouse, depending on how you did set the fishing (fishes are food).
But even if it can be a way to earn gold, if you are at the first days of your playing, my suggestion is to explore the map by trading from a port to another.

(also, better not to say in forum where your ships are )

As Shadowood and Dejanira reminded you, "fish are food," they are not friends (contrary to what others might tell you)

Thanks for the heads-up pirates. Especially to Dejanira for the reminder of location security.

Here is some good details on fishing:

Fishing Formula (Per Hour): (Ship Crew / 5) + (Cargo Capacity / 5) - Max Cannons