980 BULLETIN OF THE BUREAU OF FISHERIES. 



courses where no other salmonid could thrive. Even in the immediate neighbor- 

 hood of factories discharging waste water and refuse, where both the brook trout 

 and the char could certainly not exist, the irideus flourishes and grows fat. 

 It appears to be specially valuable for exclusively or partially populating the 

 numerous cold ponds in the forests of lower Austria, which in consequence of 

 their low temperature, severe climate, and exposed situation are less adapted 

 for carp breeding. Altogether it must be said that the irideus has fully come up 

 to all that has been expected from it in nearly every instance. 



Thus until very recently all breeders joined in a panegyric of the irideus. 

 But things have now changed. The sad discovery has been made that the 

 much-praised power of resistance of the rainbow trout in ponds against disease 

 rapidly decreases and that this fish if strongly fed nowadays suddenly shows a 

 remarkable frailty, nay an exotic weakness, which had been entirely unforeseen. 

 The most unpleasant phenomenon for the breeder is the increasing spread of 

 anaemia, which frequently causes great losses. The extraordinary weakness 

 becomes manifest in the death of numerous fish through simple sorting opera- 

 tions, the clearing out of ponds, or short transportation. Quite frequently 

 examination of the dead fish reveals no other symptoms but those of a greater 

 or less poorness of blood. The fish are pale, particularly in the gills, the regular 

 color of which ought to be a very bright red. The internal organs are also pale, 

 and the liver yellow. This organ frequently shows fatty degeneration and is 

 interspersed with hemorrhages, as the result of ruptures of the sides of the 

 vessels. Searches for any other causes, such as bacteria and parasites, have 

 proved unsuccessful. Consequently anaemia must be regarded as a symptom 

 of general deterioration of the breed. As a rule these symptoms become visible 

 in the second year, and it may be that frequently the death of the fry as well 

 as the outbreak of dropsy of the yolk sacs is due to this circumstance. As a 

 matter of course such fish are not very well qualified to act later as mother fish, 

 as they give bad eggs and sometimes remain sterile because of degeneration of 

 the sexual organs. Undoubtedly the unfitness of the rainbow trout for 

 acclimatization here is the cause of this degeneration. The conditions in which 

 the fish lives in its native country, where it migrates even at the spawning 

 time, are it appears different from those in Austria. It may therefore be truly 

 said that the rainbow trout is decreasing at a rapid rate and before long will 

 disappear from our ponds, unless there is a speedy introduction of fresh blood 

 by the importation of eggs from America. In the unfortunately somewhat 

 limited number of brooks and small rivers which for some time have been 

 stocked with irideus in a regular and rational manner, a good stock has developed 

 which spavm in open water and multiply in a natural way although not in great 

 numbers. These do not show any of the symptoms of degeneration of the pond 

 and fattened fish of this species. 



