This was my post from the other thread you opened:
'To answer your question (assuming you know how to work the city's citizens), you just go to the city view (by double clicking the city) and set one of your citizens to work the square the fish or whale is on. You can do the same for any square. If there is gold on a hill that you want to profit from, just set one of your citizens to work that square. If you don't understand how the citizens work, I'll explain it to you.'