988 BULLETIN OF THE BUREAU OF FISHERIES. 



in lethargy and without appetite; only the roaches and a few carp swam 

 slowly about. Good spawn was obtained only in ponds where there was an 

 outflow of springs; there were but few brood fish in the places where formerly 

 could be found some loo kilograms; and good roe fishes were in still smaller 

 number. In addition to this symptom of degeneration there were others in 

 an increased degree. Anaemia, however, did not appear in the rainbow or brook 

 trout. 



No food substitute whatever was given to the fish in the principal pond, in 

 order to forestall a beginning of degeneration. This, however, was without 

 avail. The regulation of the course of the principal river of the country gradu- 

 ally drained away the living water supply of the establishment; the springs 

 coming from the great subterranean stream of the Laibach field went dry, and 

 we were forced to abandon the locality in July of this year. 



It is impossible to demonstrate in a more striking way than this the neces- 

 sity of a good flow of water, one of the three conditions — infected bottom of 

 ponds, continuous use of substitute foods, and insuflicient flow of water — which 

 brings about phenomena of degeneration, the more rapidly and in so much the 

 higher degree if two or all three causes are operating at the same time. 



And what about native trout ? I would ask only when and where has there 

 been observed in this fish any greater power of resistance against the above- 

 mentioned causes of degeneration ? It is not less sensitive than the brook trout 

 and considerably more so than the rainbow. 



As to the American trouts in running streams I know of only one drawback 

 to the rainbow, namely, that there is no reason to suppose that it will remain 

 and make a constant abode in particular waters, or that it will immediately 

 leave the abode of its youth; water seemingly of the same character was in 

 reality quite different. In two cases the fry developed in four years into mature 

 fishes. The lingering of the rainbow in certain waters has astonished us as 

 often as its disappearance from the same localities. 



The brook trout shows more tendency to remain. In waters where food is 

 abundant this fish surpasses even the rainbow in rapid growth. Contrary to 

 the general opinion that it must have cool water, I saw this fish thrive one 

 summer in water having a temperature of i8° to 20° C. In small creeks, poor 

 in food, it scarcely thrives as well as the native fario. In the Stara Voda, which 

 stream I had under my control from 1901 to 1908, it grew to be the principal 

 fish after the first introduction as small fry, while only a few of the rainbow 

 trout had remained there. The native fario, which was already there and did 

 well, remained far behind the foniinalis in numbers and in rapidity of growth. 

 Only during the last two years, when the stream sufi^ered, like the establishment 



