What is the relation between production, meals and total export price?

I'm playing Tropico 4 right now, but I'm pretty sure it's the same for all Tropico games. I've finished the normal campain, but I'm still wondering what these numbers are about.

So let's take an example :

• In the "Trade" tab, I can see the "price" of fish (1 ton ? 1 fish ? 1 unit ? something else ?) is : 576 $

• Now I click on my fish farm and I can see the total export so far is : 5372 $

• The total amount of production (units ? fishes ? tons ? ...?) is 1317

• The amount of meal is 0

• The "Stock prod." is 100

So how are these numbers related ? I would expect that "total export" / "amount of production" = 5372 / 1317 = 4.08 $ would give me a number around the price of a unit, but no, not at all.

Here is a screen cap (french version) :

Same question for a random farm (Maïs probably means "Corn"), and the price in "Trade" tab is 960 :