The growth of brown trout (Salmo trutta Linn.); factors influencing the growth of trout fry.

It has long been known that brown trout (Salmo trutta Linn.) grow to different sizes in different waters, and there has been much speculation concerning the factors determining these differences. Dahl (1918-19) suggested that the food supply and the degree of crowding were important; also that small, slowly growing trout were derived from smaller ova than those growing more rapidly. Southern (1932, 1935) demonstrated that, in Ireland, the rapidly growing fish are found in hard or alkaline waters, while those growing slowly live in soft, acid waters. This correlation has been upheld by the work of Frost (1939, 1945), Went & Frost (1942) and Went (1943) for Ireland, and by that of Raymond (1938) and Swynnerton & Worthington (1939) for Great Britain, though exceptions were reported in the Salmon and Freshwater Fisheries Report for 1936.