Generally, influent-water temperatures in Norway are below the temperature range for optimal growth (14–18 8C, Austreng et al., 1987) for most part of the year at most sites (Fig. 1), the exceptions being sites utilizing industrial cooling water. At early life stages up through start-feeding, heating of water is extensively used to obtain faster growth. Due to high water volume requirements, heating of water is not utilized at later life-stages, and most of the one-year-old smolt (S1) groups released in the spring are grown at ambient temperatures from June first summer after hatch. The temperatures during the summer months are in most cases sufficiently high to obtain good growth rates during the final stages of autumn smolt (S0) production. Few data available from Chilean inlet-water make generalisations difficult, but all available information suggests much less annual temperature variation and more optimal temperatures.