Fish farms raise fish in controlled or managed environments for food production. In the UK, these businesses commonly produce species such as salmon and trout, using freshwater ponds, tanks or river-based systems, as well as marine cages. Some farms operate hatcheries, breeding adult fish and raising eggs and young fish before transferring them to growing facilities. Production methods vary according to the species, site and type of system used. Typical activities include monitoring water quality and temperature, managing feeding and fish health, maintaining tanks, ponds, cages and other equipment, and recording growth and stock levels. Fish are generally harvested when they reach a suitable size and may be sold whole or supplied for further processing, smoking or preparation by other businesses. Some farms also provide fish for restocking rivers and lakes, or sell directly to retailers, restaurants and consumers.