Those with access to fish ponds had a controlled source of food, not unlike pastures for cattle and sheep, for use on days when it was not permitted to eat meat. However fish ponds were difficult to maintain. They were a mark of power and authority, since only rich nobles and institutions such as monasteries could afford to maintain them. In winter, supplying fresh food for a castle garrison was a constant struggle. Nobles had access to meat from deer parks, but this did not supply the needs of whole households. Though fish ponds required maintenance to keep them healthy, they were an elegant way of giving monasteries and noble houses access to fresh fish.