66 U. S. BXTEEAU OF FISHERIES. 



serve to show how much the growth of a brown trout is affected by its sur- 

 roundings and food supply. The species has been known to become sexually 

 mature when 2 years old and 8 inches long. 



Habits. — The brown trout thrives in clear, cold, rapid streams and at the 

 mouths of streams tributary to lakes. In its movements it is swift, and it 

 leaps over obstructions like the salmon. It feeds usually in the morning and 

 evening, is more active during evening and night, and often lies quietly in 

 deep pools or in the shadow of overhanging bushes and trees for hours at a 

 time. It feeds on insects and their larvfe, worms, moUusks, and small fishes, 

 and, like its relative, the rainbow trout, it is fond of the eggs of fishes. In 

 Europe it is described as rising eagerly to the surface in pursuit of gnats, and 

 it is said to grow most rapidly when fed on insects. 



Reproduction. — Spawning begins in October and continues through December 

 and sometimes into January. The eggs are from one-sixth to one-fifth of an 

 inch in diameter and yellowish or reddish in color : they are deposited at inter- 

 vals during a period of many days in crevices between stones, under projecting 

 roots of trees, and sometimes in nests excavated by spawning fishes. The 

 parents cover the eggs to some extent with gravel. The hatching period varies 

 according to temperature from 40 to 70 days. F'emales aged 3 years furnish 

 on the average about 350 eggs each, but individuals of this age have yielded as 

 many as 700, and even at the age of 2 years some females produce from 400 to 

 500. When they are 4 to 5 years old, the number of eggs has reached 1,500 to 

 2,000. The young thrive in water with a temperature of about 50° F. Sterility 

 in the females is common, and breeding females have been observed to cease 

 reproduction when 8 years old. 



Qualities. — The brown trout is in its prime from May to the last of September. 

 Its flesh is very digestible and nutritious and deeper red than that of the 

 salmon when suitable food is furnished. The flavor and color, however, vary 

 with food and locality. Insect food produces the most rapid growth and best 

 condition. This species has been so long known as one of the noblest of the 

 game fishes, and its adaptability for capture with artificial flies because of its 

 feeding habits is so well understood that I need not dwell on these familiar 

 details. 



DISEASES COMMON TO TROUT UNDER DOMESTICATION 

 AND THEIR TREATMENT. 



Trout in artificial environment are subject to various ailments, and 

 little definite knowledge is available as to the causes or prevention of 

 such ailments. The more simple and obvious preventive measures 

 are (1) the utmost cleanliness in and about the hatchery, troughs, 

 and ponds, and all ecjuipment used in connection therewith; (2) care- 

 ful handling of eggs, fry, fingerlings, and adult fish at all times; (3) 

 a carefully selected diet of materials free from contamination of any 

 kind; (4) an abundant flow of uncontaminated water through all 

 ponds and troughs. 



Most of the diseases to which trout fingerlings and adults are sus- 

 ceptible may be traced to some form of parasitic animal. Where 

 these parasites attack the fish externally a number of methods of 

 treatment, all more or less effective, have been prescribed. One of 

 the most simple of these consists in immersing the affected fish_ in a 

 solution of salt or cider vinegar. More recently certain chemicals, 

 including copper sulphate and potassium of permanganate,^^ have 

 been used with success. In certain instances bicarbonate of soda, ap- 

 plied with a brush to the affected parts of adult fish, has proven 

 efficacious. 



Parasites occurring in the intestines or other internal organs are 

 less responsive to treatment, and internal medication of fish of any 



«A New Bacterial Disease of Fresh- Water Fishes. By H. S. Davis. Bulletin, of the 

 Bureau of Fisheries, Vol. XXXVIII, 1921-22. Bureau of Fisheries Document 924. 



