The Fishing Pier is the first source of income for the game. All other economies derive from this basic commodity. Each time after upgrading the Fishing Pier, allow your boats to finish their current cycle and fall asleep. The next time you click on them, they will be at the new higher rate of productivity.
After the 28.06.2016 game updater the graphics of fishing boats was updated, so that each level of Fishing pier has it unique Boats visuals.