The Fish Basin and Wood Stack are inextricably linked. You need as much fish as you can hold to upgrade your wood and vice-versa. You'll also have to have max Vikings for your Meade Hall level and you always need to upgrade your basins before upgrading your Academy. The Fish Basin is one of the main resources storage buildings in the game. The bigger your Fish Basin is the more File:Fish.png you get in Toothless' bags from Special Events.