Apparatus for precise regulation and chilling of water temperatures in laboratory studies

Laboratory simulation of water temperature regimes that occur in subarctic rivers through winter necessitates the ability to maintain near‐freezing conditions. A heat‐exchanging apparatus is described that provided a convenient means of simulating the range of temperatures (0.5–12°C) that incubating eggs of salmon (Oncorhynchus spp.) typically experience in south‐central Alaskan watersheds. The system was reliable, easily maintained precise temperatures at our coldest test levels, and was used over several years with few mechanical complications.