ABSTRACT
Temperature is a limiting factor in the distribution of many animals. The ova of brown trout (Salmo trutta) can develop without excessive mortality at water temperatures between 3 and 15o C. (Gray, 1928), while for adult trout, mortality is high above 20 and complete above 25o C. (Gardner & Leetham, 1914; Audigé, 1921 ; Gardner, 1926). It is generally assumed that temperature is the most important physico-chemical factor affecting the growth of fish, especially in temperate zones, where there is an annual variation. Allen (1940) deduced from examination of salmon scales from British rivers that parr do not grow when the water temperature is less than 7°C. Pentelow (1939) and Wingfield (1940) observed the growth of yearling trout in tanks where the temperature varied with that of the external environment and was recorded once a day. They found that there was no growth at temperatures less than 6°C., and it was most rapid between 10 and I5°C. Since other environmental factors varied at the same time, the correlation between growth rate and temperature was necessarily approximate.
