Young salmon and trout ordinarily take little food from about 10 p.m. to about 5 a.m. This does not seem to be entirely due to changes in temperature or light conditions. It seems probable that the fish are habituated to sleep during the hours of darkness when less food is available. A slight depression in feeding also occurs at mid-day due to rising temperature and, possibly, strong light. Extremely high temperatures at first depress, then bring about a complete cessation of feeding. After exposure to high temperatures salmon and trout will not take food again for some time, even if they find themselves in rather cool water.