.384 XJ. S. BUKEAU OF FISHERIES 



about the same percent of the fats when the level in the diet was 7 

 and 25 percent. Fats were digested to about the same extent by 

 trout weighing 2 grams and those weighing 100 grams. 



Selective hreeding. — Experiments in selective breeding of brook 

 trout were conducted at the Pittsford (Vt.) station under the direc- 

 tion of R. F. LfOrd. At the beginning of the year, 43 lots of finger- 

 ling trout were being held in small compartments in hatchery troughs. 

 Each lot was composed of the progeny of a single pair of selected 

 fish. The parent fish were in their third year and averaged 12.9 

 inches in length with an average weight of 16.6 ounces in the case 

 of the females, while the average weight of the males was 18.2 ounces 

 and the length 13.6 inches. Such differences in the sizes of male and 

 female brook trout of the same age are quite typical. 



The young fish were kept under strict observation, and late in the 

 spring those lots which did not reach the desired standard were dis- 

 carded. The remaining lots were reduced to 400 fish each, which 

 were kept segregated during the summer. The surplus fish from 

 these lots were retained for general brood stock. 



At the close of the season the various lots were carefully compared 

 and only the very best lots with regard to growth, resistance to 

 disease, and hereditary background were retained. 



As indicated in previous reports, the results of these experiments 

 in selective breeding have been very gratifying. There has been a 

 remarkable increase in the o^gg production and rate of growth of 

 selected fish and also an improvement in resistance to disease. Simi- 

 lar experiments with rainbow and brown trout are being carried on 

 at the Leetown station, but there has not yet been time for these 

 experiments to show material results. 



Experiments in rearing exotic S2)ecies. — The Pittsford brood stock 

 of Montana grayling was stripped for the third time in the spring 

 of 1934. A good hatch was obtained from these eggs, and about 

 6,000 fingerlings were retained for wintering. It is planned to use 

 these fish to stock a pond which has recently been built in the Green 

 Mountain National Forest. A stock of grayling derived from eggs 

 shipped from Pittsford is also being reared at the Leetown station. 

 These fish have done very well, and it is expected they will produce 

 €ggs in the spring of 1936. 



Excellent results were obtained from a small lot of golden trout 

 {Salvelinus aureohis) eggs from Lake Sunapee, N. H., which were 

 shipped to Pittsford in the fall of 1933. The fingerlings were car- 

 ried through the summer with very little loss and by fall many of 

 them had reached a length of 6 inches or more. A tendency of the 

 fish to crowd together at one end of the trough was overcome by 

 excluding the light. 



A stock of California golden trout {Sahno aqua-honita) is also 

 being reared at the Pittsford station. These fish are quite susceptible 

 to furunculosis, and considerable losses have occurred from this 

 disease; but in other respects they appear to be no more difficult to 

 rear than other species of trout. 



Field studies. — An investigation of the results of planting a certain 

 number of rainbow trout fingerlings in a 1-mile section of a spring- 

 fed stream near Leesburg, Va., was continued by E. W. Surber, in 

 charge of the Leetown station. In addition to collecting data on the 



