PROGRESS IN BIOLOGICAL INQUIRIES, 193li 133 



stock such as were used in the feeding experiments. The lot making 

 the greatest growth of those on experimental diets had an average 

 individual weight of 6.09 grams on September 3, while one lot of 

 selected fish on the same diet had an average weight of 12.7 grams 

 on September 7. Another lot had an average weight of 12 grams 

 and several lots averaged 10 grams or more. These results are the 

 more striking when it is considered that the general brood stock has 

 been improved by mass selection during this time, so that the average 

 weight of fingerlings kept on a diet of beef liver during the summer 

 has increased from 2.2 to 4.4 grams. 



The increase in egg production as a result of selective breeding is 

 equally gratifying. The average number of eggs produced at the end 

 of the 'third summer (that is, by fish commonly known as 2-year-olds) 

 was 958 in 1928 and 1,779 in 1932. These fish were selected as the 

 best available fish of their age. 



Additional data, showing the importance of heredity in determin- 

 ing the date at which trout spawn, was obtained during 1932. In 

 one lot of fish containing thirty-eight 2-year-old fernales 33 were 

 ready to spawn on November 8. The eggs from which these fish 

 were hatched were taken November 9, 1929. In another lot contain- 

 ing 28 females, 25 fish were ripe November 8. The spawning date 

 of^the parents of these fish was November 8, 1929. In several other 

 lots the results were nearly as striking. 



Evidence was also obtained indicating that it will be possible to 

 develop a strain of brook trout more resistant to furunculosis than 

 the average fish of this species. Two lots of fish hatched in 1930 

 from mated pairs have shown a marked resistance to the disease, the 

 percentage of survivors being much greater than in any other lots. 

 Owing to the fact that it is very difficult to eradicate furunculosis 

 after it has become established at a hatchery, the devc'lopment of a 

 resistant strain of fish offers one of the most promising means of 

 combatting the disease. 



Observations on recently liberated trout. — The belief appears to be 

 increasing among anglers and others that trout reared at hatcheries 

 are inferior to wild fish in several respects, and especially in their 

 ability to forage for themselves. This may be true to a certain ex- 

 tent, but there is httle definite information on which to base an 

 opinion. In order to throw more light on this problem 100 yearhng 

 brook trout, averaging 7 to 8 inches in length, were hberated in a 

 trout brook running through the grounds of the Pittsford station. 

 These fish were marked by removal of a pelvic fin and liberated on 

 August 18 shortly after the close of the fishing season. Up to the 

 time of their hberation these fish had been held in one of the hatchery 

 pools, with concrete sides and gravel bottom. They had been fed the 

 regular hatchery diet of dry salmon eggs and fiver, and were vigorous 

 well-proportioned fish. Beginning 24 hours after the fish were hber- 

 ated daily samples were taken on artificial files and the stomachs 

 preserved for study. 



It was found that these trout took the fly with the same zest dis- 

 played by other fish taken in the course of the study and apparently 

 gave the anglers as much "fight" as fish reared in natural surroundings. 

 As in the case of the wild fish, it was found impossible to inveigle any 

 of the hatchery trout into taking the fly on certain days, and it was 

 concluded that they were not appreciably easier to capture than wild 

 trout. 



